Electronic Computer Projects for Commodore and Atari Personal Computers Soon Sivakumaran COMPUTE! Publications,!^ Part of ABC Consumer Magazines, Inc. One of the ABC Publishing Companies Greensboro, North Carolina Copyright 1986, COMPUTE! Publications, Inc. All rights reserved. Reproduction or translation of any part of this work beyond that permitted by Sections 107 and 108 of the United States Copyright Act without the permission of the copyright owner is unlawful. Printed in the United States of America 10 987654321 ISBN 0-87455-052-1 The author and publisher have made every effort in the preparation of this book to insure the ac- curacy of the programs and information. However, the information and programs in this book are sold without warranty, either express or implied. Neither the author nor COMPUTE! Publications, Inc., will be liable for any damages caused or alleged to be caused directly, indirectly, incidentally, or consequentially by the programs, information, and/or projects in this book; nor liable for any accidents or errors in the implementation of the projects, the handling of any materials for the projects, and for any damage that may result to any individual or equipment. The opinions expressed in this book are solely those of the author and are not necessarily those of COMPUTE! Publications, Inc. COMPUTE! Publications, Inc., Post Office Box 5406, Greensboro, NC 27403, (919) 275-9809, is part of ABC Consumer Magazines, Inc., one of the ABC Publishing Companies, and is not associated with any manufacturer of personal computers. Atari, Atari 400, Atari 800, Atari XE, and Atari XL are trademarks of Atari Corporation. Commodore 64, Commodore 128, and VIC-20 are trademarks of Commodore Electronics Limited. Radio Shack is a trademark of Tandy Corporation. Contents Foreword v Preface vii 1 Getting Inside Your Computer 1 2 Exploring the Control Port 7 3 Making a Joystick 21 4 Game Paddles 31 5 An Analog Light Sensor 43 6 A Light Pen 51 7 A Digital Light Sensor 65 8 An Electronic Switch 79 9 A Burglar Alarm 95 10 Digital Logic 107 1 1 A Better Logic Probe 121 12 More Ideas 127 1 3 Robotics 1 49 Appendices 163 A COMPUTEI's Guide to Typing In Programs 165 B Integrated Circuits 171 Index 181 Foreword Your personal computer is a powerful machine. It can calcu- late faster than any clerk, print documents faster than any typ- ist, and play chess with the masters. Your software library is probably full of such applications, along with games, utilities, and educational software. But a computer can do a lot more than run software. It can be a sophisticated controller which turns lights on and off, monitors your home's windows and doors, and makes robot limbs move. To accomplish these tasks, however, you need sensors, motor circuits, and other electronic devices. That's why you need Electronic Computer Projects. This book is a step-by-step guide to building a variety of electronic devices, from the simple to the sophisticated. With complete and concise instructions anyone can follow, and ac- companied by detailed photographs and figures, Electronic Computer Projects is the book with which you can teach your Commodore or Atari personal computer valuable new tricks. Parts lists outline what you need, the instructions show you how to do everything from heating the soldering iron to plug- ging in the last component, and programs test and adjust each project. Learn how to build your own joysticks, game paddles, and light pens. See how to put together two kinds of light sensors, even how to create a burglar alarm with an infrared sensor that "sees" in the dark. Logic probes, which let you "look" into digital circuits, multiplexers and demultiplexers, even robotic motor control circuits are all part of this book's intrigu- ing and educational projects. Each project has been built and tested — you won't find any surprises when you connect a de- vice to your computer. Electronic Computer Projects is a thorough guide to your ad- venture into computer control of the outside world. Preface Computers are versatile machines which can be programmed to perform tasks quickly and accurately. These tasks, or appli- cations, run the range from games and word processing to fi- nancial modeling or controlling the lights and heat in your home. Most computer applications, at some point in the process, involve a program which processes data, or information. A video arcade game is a good example. Here, the data is en- tered by the player through a joystick — the processing the program performs is the motion of the character on the screen. Another example, word processing, lets you enter text (the data) and process it (by formatting it properly and printing it out). These kinds of applications are certainly useful, but they aren't the end of your computer's capabilities. A vast majority of computer applications are limited to act- ing only on data entered by the user, either from the keyboard or the joystick. Yet some of the most interesting applications result when computers interact with the outside world. A com- puter which can examine its surroundings can then use this information to perform a useful function. Imagine your com- puter, sensing that it's now dark outside, turning on your out- side lights before you arrive home from work. Computers have made possible systems which can control extremely complex operations. The software, or programs which instruct a computer to do a specific task, is in fact a form of intelligence — if written correctly, the programs can re- act to different conditions in predetermined ways. This book will show ways you can use your computer to re- late and react to the outside world. This is done through sen- sors and actuators. Sensors gather information from the outside world for the computer to process. Actuators allow the com- puter to influence outside events. Several of the projects put sensors and actuators together so that the computer can per- form a given task. To help you get started, the first few projects in this book are relatively easy to complete. As your experience increases, vii Preface so does the difficulty of the projects. If you're new to electron- ics, then, start with the first projects in the book, developing your skills as you progress toward the later, more difficult, projects. But even though the projects increase in difficulty, you won't need any exotic equipment or advanced skills to complete them. Almost all the projects contain less than a half-dozen com- ponents. You'll have little difficulty with any of the projects, but you should have some understanding of electronics trouble- shooting procedures. Building a Circuit The basic idea when building a circuit is to wire together the components' leads correctly. Occasionally, even experienced builders make mistakes in wiring circuits. It's an excellent idea to completely read through each section describing the circuit's construction before starting. Color-coded wires can help in tracing circuits. Examine the drawing of the breadboard layout included in the book, and study the schematic diagram. When you feel you understand what the circuit requires, go ahead and wire your test circuit. Several methods of wiring, or breadboarding, circuits are available and suitable for the projects in this book. One method involves mounting the components on a perforated board. The components are positioned on one side of the board so that their leads extend through the perforations to the opposite side. The leads on the bottom are then connected by wires soldered between them. A similar method, called wire wrapping, requires that each component be mounted in a socket before being placed on the perf board. Each socket has metal posts which make contact with the leads of the component. The posts extend through the holes. Wire connections are made by wrapping one end of a wire around one post and the other end of the same wire around a second post. This is done with a wire wrap tool. Most commercial electronic circuits, however, are con- structed using printed circuit boards. Printed circuit boards are copper plated on one or both sides. When making a circuit viii Preface using printed circuit boards, you must first determine the loca- tion of components on the board. Then, the interconnections between the components' leads are marked on the board with an indelible felt-tip marker. The board is submersed in a chemical solution which dissolves all copper from the board except that along the traces you've marked. The copper traces which remain form the connections between the components. Commercial manufacturers prefer this technique because boards can be produced in large quantities quickly and cheaply with photographic techniques. Your best bet is to use solderless breadboards, like those available from Radio Shack. (Radio Shack's Experimenter Socket, part number 276-174, was used to construct all the projects in this book.) A solderless breadboard is a plastic board with a grid of "holes" called plug points (see Figure 1). The plug points are internally wired so that the columns of points on each half of the board are connected. A row of plug points on each half of the board are connected as well. To hook up a circuit, compo- nents are just plugged into the solderless breadboard. A con- nection between two component leads can be made simply by inserting each lead into plug points that are internally con- nected. No soldering is required. Alternatively, jumper wires can be used to bridge one set of connected plug points with another to complete a connection. Jumper wires should be #22 gauge, as larger wires tend to spread the contacts of a plug point too far apart, eventually ruining the breadboard. These solderless boards may be reused for different experiments without removing solder from connections. Most wiring ex- planations in this book refer to coordinates on the solderless breadboard. Heat the Iron Even if you use a solderless breadboard when constructing the circuits in this book, you'll still have to do a little soldering. While you won't have to do intricate soldering, wires still must be attached to switches, the connectors which plug into your computer, and other components that cannot be directly ix Preface • i * • * •—- • — » — * — • * e * # c o a a> 3 a O £ Preface plugged into a solderless breadboard. Soldering is the only re- liable method of making these connections. To make solder connections, you need a pencil soldering iron (approximately 25 watts) and some electronic resin core solder. Make sure the solder you use is suitable for electronic work — some types of solder used in other applications use a corrosive resin. The steps to make a solder connection are listed below. Try soldering some practice connections with scraps of wire before soldering on one of the projects. 1. Make sure the joint you're going to solder is free of dirt and grease. The solder will not bond properly if it's not clean. 2. Try to make the joint as firm as possible before soldering. If you're joining two wires, twist them together. When con- necting to a terminal, like that of a switch, twist the wire around it. Doing this makes the connection more reliaible, as a dab of solder by itself will not hold a connection to- gether for long. If you're using stranded wire, twist the strands together before making the connection. This will prevent stray strands from shorting out nearby connections. 3. When you're soldering an electronic component such as a transistor or IC (integrated circuit) chip, attach an alligator clip to the lead of the component just above the point where you're going to make the connection. The metal alli- gator clip acts as a heat sink, drawing heat away from the component, preventing damage. 4. Plug in the soldering iron and wait until its tip is hot enough to melt solder. 5. Touch the tip of the soldering iron to the joint and wait a couple of seconds for it to heat up. 6. Touch the solder to the joint, not the tip of the soldering iron. Remember always to heat the work surface, not the solder. Some solder should flow onto the joint. Remove the remaining solder from the joint and then remove the solder- ing iron. A minimum amount of solder should be used when making a connection. Excess solder not only looks sloppy, but can cause short circuits. xi Preface 7. A good solder connection is bright and shiny. If it's a dull gray, you have what's called a cold joint. If this happens, re- make the connection. A poor solder joint can cause an other- wise perfect circuit to fail. 8. Sometimes it will be necessary for you to tin, or coat, the leads to a component with a thin coating of solder before establishing a connection. Tinning helps remove oxidation and cleans the service, providing a better electrical and me- chanical connection. 9. When you're finished soldering, wipe the tip of your solder- ing iron on a damp sponge to remove any excess solder and resin. The tip should be a silver color, without any trace of dirt or foreign objects. This practice will increase the useful life of the tip. Be sure to unplug the soldering iron as well — an unattended hot iron is a fire hazard. In Your Toolbox Besides a soldering iron, there are a few other tools you'll need. A pair of small wire cutters and a wire stripper are handy, but you can strip insulation from a wire with a knife if you're careful not to nick the conductor. Needle-nose pliers are useful for twisting and untwisting wire, and for reaching tight spots too small for your fingers. A drill and a screwdriver are required for some of the projects to mount the circuits in a case. Since you'll be working with integrated circuits (ICs), an IC extractor will be handy for removing the IC chip from the cir- cuit board. You'll find that the pins of the ICs are very easy to bend. If the circuit doesn't give the results you expect after you've carefully built it, compare your circuit to the diagram in the book. Are all the pins properly connected? Is the IC inserted correctly? Have you entered the program designed to use the circuit properly? Most programs included with this book are short, so you should have little trouble entering them cor- rectly. To make this part of the job even easier, use "The Automatic Proofreader" found in Appendix A — it's an error- xii Preface checking program which insures that you type in the program correctly the first time. Each circuit described in this book has been thoroughly tested. The circuits and the demonstration programs will work as explained in the text, providing you follow the instructions carefully. All projects are designed to operate with the Commodore 64, Commodore 128 (in 64 mode), and VIC-20, and with the Atari 400, 800, 600XL, 800XL, and 130XE personal computers. The electronics involved is virtually identical for all these com- puters, but the programs differ. Be sure to use the correct pro- gram for your computer. Have fun building the projects. Experiment with your own ideas. By the time you've finished the last project, you should understand how to interface your computer to almost any- thing. At that point, your own imagination will take control. Help's on the Way To make it easier for you to use this book, you'll see small graphic devices, called icons, throughout the book. These cues will alert you to specific sections of each chapter: shows you where the parts list for each project is located. The number of components, their names, and their Radio Shack part numbers are provided. points out where the step-by-step instructions for building each project begin. Steps are numbered and are self-explanatory for the most part. indicates that a testing procedure is described, or that a program will follow. After you've finished a project, you'll almost always be shown ways to test it under working conditions to insure that it operates as advertised. calls your attention to various warnings and/or notes on a project. xiii CHAPTER 1 Getting Inside Your Computer Getting Inside Your Computer A computer is really nothing more than a series of switches. Of course, it's a highly complex series of switches. Thousands and thousands of them. Like any switches, those you find in a computer can have two positions, on or off. Storing information in a computer is simply a matter of setting a se- quence of switches on or off. If the switch is on, its value is 1 . If the switch is off, it holds a value of 0. The digital circuits used in computers are switches which perform a specified series of ac- tions, all based on the information in the on and off states of the circuit. Everything in a digital cir- cuit is either on or off, unlike analog circuits, found in things like radios and televisions, which deal with voltage levels and signals. Analog cir- cuits may amplify or otherwise modify electronic signals of various levels. These on and off states within a computer are represented as electronic signals of two different voltage levels. In the computers this book deals with, an on state corresponds to a signal of about + 5 volts, while the off state corresponds with a signal of about volts. (Actually, a positive volt- age more than 2.5 volts is considered on, and a voltage less than 0.5 volts is considered off. This is called a TTL, or transistor-transistor logic signal level.) Since a switch can exist in only two states, on or off, what information can be represented? Sim- ple — one of two numbers. The on state can be as- signed to mean the number 1, and the off state can be the number — the two digits which make up the base two binary number system. The bi- nary number system naturally lends itself for use 3 CHAPTER 1 with the digital logic circuitry in a computer. Un- fortunately, we're used to counting by ten. The number 65, for instance, has far more meaning to us than its binary equivalent, 1000001. Dealing with numbers at the binary level is best left to the computer, but when you're trying to in- terface your computer to the outside world, it's often necessary to know and understand how set- ting a bit in a memory address within the com- puter affects the machine and its operation. Number Systems The binary number system is just another way of representing numbers. The number system we normally use, the decimal number system, is a base ten number system. In other words, there are ten different symbols (0, 1, 2, 9) which can be used independently or in combination to represent a given number. The value of the number repre- sented depends on both the combination of sym- bols and their relative positions. Let's take a look at how a decimal number is made up, for example 37,506. Position 43210 Decimal number 37506 Decimal Symbol Base Position Value 3 10 ~4 = 30,000 7 * 10 '3 7,000 5 * 10 "2 500 * 10 "1 6 * 10 A o 6 37,506 As you can see, the first symbol, 3, represents three times ten to the fourth power (in other 4 Getting Inside Your Computer words, a 3 followed by four zeros). In the same manner, each symbol represents a number multi- plied by a power of ten (the power is determined by the symbol's relative position). Adding all these values together gives us the number 37,506. The binary number system has just two sym- bols, and 1. A Binary digiT, or bit, can thus be either or 1. One bit by itself can only be used to count up to one. Larger numbers in binary, as in the decimal number where you can represent larger value numbers with more digits (a number like 245 requires three digits, whereas the number 4 requires just one), are represented by more bits. As you can see in the following example, a binary number is made in a similar manner as a decimal number. Position 76543210 Binary number 11111001 Decimal Symbol Base Position Value 1 * 2 y 128 1 * 2 % 64 1 * 2 *5 = 32 1 * 2 '4 16 1 * 2 ~3 8 * 2 '2 * 2 "1 1 * 2 ~0 = 1 249 Just as with the more comfortable decimal num- bers, binary numbers are built by combining sym- bols, then multiplying those values by two (since binary is base two) raised to the power of the symbol's position. A 1 in the seventh position, then, represents the decimal value 128, while a 1 in the first position only represents 1. 5 CHAPTER 1 Here are a few more examples of how decimal numbers (what we use) are represented as binary numbers (what computers use). Try working them out to see if you come up with the same values. Decimal Binary 10 = 1010 5 = 101 134 = 10000110 Chock Full of Bits In computers, bits are usually put together in groups of eight when stored or otherwise manipu- lated. A group of eight bits is called a byte. Since it has eight positions, a byte can hold any number from 00000000 binary (0 decimal) to 11111111 bi- nary (255 decimal). The largest number which can be represented by a byte, then, is 255. These binary values are used by the computer for all its operations, from executing an applica- tions program to representing alphanumeric, even graphics characters. Understanding the elements of the binary num- ber system, bits, and bytes will prove useful as you move into the heart of Electronic Computer Projects. The next chapter, "Exploring the Control Port," is your start toward your own custom-built computer projects. 6 u CHAPTER 2 ■ Exploring the Control Port Exploring the Control Port With a basic understanding of how a computer operates, you can now begin exploring the com- puter's ports, the gateways through which infor- mation flows into and out of your computer. The ports are often referred to as I/O ports, which stands for input / output ports. Though there are several different I/O ports on your computer, the projects in this book use one port in particular, the joystick port. The joystick port provides plenty of access to your computer for our demonstation circuits. Con- nectors for this port are also commonly available. They are the same type as those found on joy- sticks and game paddles — D-subminiature female connectors. Figure 2-1 . The Joystick Port- Control Port 1 Control Port 2 (Commodore 64) Pin Type Pin Type 1 JOYAO 1 JOYBO 2 JOYA1 2 JOYB1 3 JOYA2 3 JOYB2 4 JOYA3 4 JOYB3 5 POT AY 5 POT BY 6 Button A/LP 6 Button B 7 + 5 volts 7 + 5 volts 8 Ground 8 Ground 9 POT AX 9 POT BX 9 CHAPTER 2 The joystick port has nine pins. Pins 1, 2, 3, 4, and 6 are I/O pins. They are connected to wires which may be used to communicate binary (on/ off) data. Pins 5 and 9 are used to input analog data — we'll learn more about these pins later in the book. Pin 7 is connected to a +5-volt source, while pin 8 is connected to the power supply ground. Once you can identify the pins of a control port, your next step is to understand how they can be used. A few homemade "tools" will help. A Simple Logic Probe A logic probe is a device that lets you "look" into what's going on in a digital circuit. It's a device that tells you whether a 1 (high state) or a (low state) is present at a point in the circuit. A simple logic probe can be assembled from two main com- ponents. This logic probe can be used to see how the I/O lines of the control port are used to input information. To construct the logic probe, you'll need these parts: Part Quantity Part Number 1 Light-emitting diode (LED) 276-041 1 IK ohm resistor 271-8027 2 Alligator clips 270-378 You'll also need some stranded copper wire (about #22 gauge — Radio Shack part number 278- 1307) to make the probe leads, as well as some electrical insulation tape. (In this book, all part numbers are Radio Shack part numbers.) 10 Exploring the Control Port Figure 2-2. Commodore 64, VIC-20, and Atari Joystick Ports The joystick ports for the Commodore 64 (top). Commodore VIC-20 (middle), and Atari 800XL (bottom) are shown in these photos. Note that the VIC-20 has only one joystick port. CHAPTER 2 Here's the procedure for putting together your simple logic probe: 1. Cut two pieces of stranded copper wire about 10 inches long. One wire will be the ground lead, while the other will be the probe lead of this simple logic probe. 2. Strip about a half inch of insulation from each end of both wires and attach an alligator clip to one end of each wire. 3. Solder the free end of one wire to the anode of the light-emitting diode (LED). Usually, the an- ode leg of an LED is the shorter of the two legs, but this may vary with manufacturers. The wire connected to the LED's anode is the probe lead of the logic probe. Note: An LED lights up when current passes through it in the proper direction, which is from anode to cathode. LEDs come in various colors, but the most common are red and green. An LED will conduct current in only one direction. It's im- portant that you don't confuse the anode and the cathode leads. In fact, if an LED fails to work in a circuit, the first thing to check is whether it's been installed correctly (see Figure 2-3). The cathode lead is usually the longer of the two leads. Figure 2-3. A Typical LED Anode (+) Cathode (-) 12 Exploring the Control Port 4. Solder the cathode of the LED to one end of the IK ohm resistor. 5. Solder the other end of the IK ohm resistor (brown, black, and red bands) to the free end of the second wire. This second wire is now the ground wire of the logic probe. 6. To complete your simple logic probe, cover your soldered connections with some electrical insu- lation tape. This will prevent short circuits from occurring while you use your probe. Note: Resistors limit the flow of electricity in a cir- cuit and are measured in ohms. The value of a re- sistor is indicated by its colored stripes — usually there are four. The first two stripes' colors repre- sent numbers as determined by the resistor color code (see Table 2-1). These numbers are the first two digits of the resistor value. The third stripe is the multiplier. The number corresponding to the multiplier color is the power of ten by which the first two numbers are multiplied (an easy way to remember it is simply to add x number of zeros to the first two numbers, where x is the multiplier color's value). All three numbers are combined to give the value (in ohms) of the resistor. Thus, a resistor which has as its first three stripes (as the one you're working on has) Brown Black Red will have a resistance of 1000 ohms. The brown stripe provides the 1, the black stripe gives the first 0, and the red stripe provides the next two 0's (10 X 10 2 ). The fourth stripe represents the resistor's toler- ance. The tolerance gives the range, plus or minus, which the actual value of the resistor will be within when compared to the strict value indi- cated by the color bands. The color of this stripe 13 CHAPTER 2 can be gold, silver, or salmon. The tolerances are plus or minus 5, 10, and 20 percent respectively. Sometimes you won't find a tolerance stripe on a resistor. This means that the resistor has a toler- ance of plus or minus 20 percent. If you have a re- sistor with brown, black, red, and silver stripes, for example, you have a 1000 ohm (IK ohm) re- sistor with a 10 percent tolerance. The actual value of the resistor is thus between 900 and 1100 ohms. The circuits in this book can all use resis- tors with a 20 percent tolerance or better. Table 2-1 . Resistor Color Codes Color Value Black Brown 1 Red 2 Orange 3 Yellow 4 Green 5 Blue 6 Violet 7 Gray 8 White 9 Tolerance Bands Color Tolerance Gold ±5 percent Silver ±10 percent Salmon ± 20 percent None ± 20 percent Resistors also have power ratings, which de- scribe the amount of energy (measured in watts) which the resistor can safely handle. For the projects in this book, you may use 1 /4- or 1 /2- watt resistors. A resistor, unlike many other circuit components, may be connected in either direction in a circuit. 14 Exploring the Control Port Figure 2-4. Schematic Diagram of a Simple Logic Probe + o- 1KB Using the simple logic probe is very easy. Attach the ground lead of the logic probe to the power supply ground of the digital circuit you're testing. Then simply touch the tip of the probe lead to a point in the circuit. If the point has a voltage of something greater than the barrier voltage of the LED, usually about 0.7 volts, the LED will glow. You can assume the point is at a logic high state (a 1). If the point is at a voltage level less than 0.7 volts, current will not flow through the diode, the LED stays off, and you can assume a logic low state (a 0) is present. (Of course, a zero indicates a voltage level less than 0.5 volts, so a problem could still exist with the circuit under test and not be detected by this simple tester.) 15 CHAPTER 2 Figure 2-5. The Completed Logic Probe When you're finished building the simple logic probe, it should look something like this. To use the logic probe to examine the joystick port, a connector is required — the next simple tool. A Connector for the Joystick Port The actual connector that plugs into the joystick port is a D-subminiature female, 9-pin connector. Stranded copper wire (#22 gauge) should be sol- dered to the terminals of the connector for easier access. Here's what you'll need: Part Quantity Part Number 1 9-pin D-subminiature female 276-1538 You'll also need some stranded copper wire (about 12 feet) or ribbon cable. The procedure is quite simple. Exploring the Control Port 1. Cut six pieces of stranded copper wire about 24 inches long and strip about 1 /4 inch of insula- tion from each end. (You may wish to use rib- bon cable instead of wire to avoid a tangle.) 2. Solder a wire to the terminals of pins 1, 2, 3, 4, 6, and 8 of the 9-pin plug. 3. Tape a tag to the opposite end of each wire with the number of the pin it's attached to. This will save you some time later. To use your logic probe with the connector, attach the ground lead of the probe to the wire from pin While your computer is turned off, insert the plug into the joystick port. (You should always make sure that the computer is turned off whenever you insert a plug into any of the I/O ports.) If you're using a Commodore 64 or Commodore 128, insert the plug into joystick port 2 on the right side of the machine. If you have an Atari computer, insert the plug into joystick port 1. Warning: Before turning on your computer, make sure that none of the wires touch each other. If any wires are touching, your computer could be damaged. Be particularly careful to inspect the wires from pins 7 and 8 — they should never be in contact. If they are, the computer's power supply could be damaged. Touch the end of your logic probe to pins 1, 2, 3, 4, and 6. Each time you do this, the LED should glow. This glow will be very faint, and you may need to shield the LED from room light to detect the glow at all. This is because of the small amount of current available at the pins. 17 CHAPTER 2 The I/O lines are connected to registers, or memory addresses, in your computer. The five pins (1, 2, 3, 4, and 6) of joystick port 2 corre- spond to the lower five bits of memory location 56320 ($DC00 in hexadecimal) in the Commodore 64 and Commodore 128. Whether you're using the port for input or output is determined by the data direction register located at 56322 ($DC02). Each bit controls the direction of data on the cor- responding bit of the port. If a bit is set to 1, the corresponding bit in the port is set to be used for data output. Setting the bit to causes the bit to be used for input. In the VIC-20, these lines corre- spond to bits in memory locations 37137 ($9111) and 37154 ($9122). In the Atari computers, you needn't worry about the memory locations af- fected, as the BASIC STICK and STRIG com- mands can be used to see the effect of the five I/O lines. The bits in these registers are normally set on (1) in your computer — that's why the LED of your logic probe should glow faintly when you touch the probe to any of these pins. But how can these pins be used to input information? Type in and run the appropriate version of Pro- gram 2-1. Program 2-1 — Commodore 64/128 EX 10 A=56320:REM FOR PORT 1 USE 56321 FQ 20 IFPEEK ( A ) AND ( 2 T ) THEN40 PH 30 PRINT "PIN 1" RM 40 IFPEEK ( A ) AND ( 2 T 1 ) THEN60 SK 50 PRINT "PIN 2" MG 60 IFPEEK (A) AND ( 2?2 ) THEN80 BP 70 PRINT "PIN 3" SQ 80 IFPEEK ( A ) AND ( 2 T 3 ) THEN100 ER 90 PRINT "PIN 4" AD 100 IFPEEK (A) AND ( 2?4 ) THEN120 SJ 110 PRINT "PIN 6" SM 120 GOTO 20 18 Exploring the Control Port Program 2-1 —VIC 20 AH 10 A=37137 BS 20 IFPEEK(A)AND( 2T2 )THEN40 PH 30 PRINT "PIN 1" GF 40 IFPEEK (A) AND ( 2T3 )THEN60 SK 50 PRINT "PIN 2" SA 60 IFPEEK (A)AND( 2 T4)THEN80 BP 70 PRINT "PIN 3" BX 80 POKE 37154, : IFPEEK ( 37 152 ) AND ( 2 T7 ) THEN100 ER 90 PRINT "PIN 4" XE 100 POKE 37154,255 :IFPEEK(A)AND(2T5)T HEN120 SJ 110 PRINT "PIN 6" SM 120 GOTO20 Program 2-1 — Atari FP 10 IF STICK(0X>14 THEN 20 EP 15 PRINT "PIN 1 " SA 20 IF STICK(0)<>13 THEN 30 FB 25 PRINT "PIN 2" BA 30 IF STICK<0X>11 THEN 40 FD 35 PRINT "PIN 3" DH40 IF STICK<0><>7 THEN 50 FF 45 PRINT "PIN 4" DN 50 IF STRIB(0)<>0 THEN 60 FI 55 PRINT "PIN 6 " AA 60 SOTO 10 When you run the program for your computer, nothing should seem to happen at first. Take your logic probe and touch the probe to the wire con- nected to pin 8. This is the ground from the com- puter and should still be connected to the ground lead of the probe. Obviously, the ground lead and probe lead are at the same potential. The LED will not light. Since ground voltage corresponds with the off state, everything is working correctly. 19 CHAPTER 2 Now, take the wire from pin 1 and touch its free end to the wire from pin 8. When you do this, you force the normally on pin 1 to turn off. Your program tells you this. If you look at the computer screen, the message, PIN 1 should be displayed on the screen. As you touch the wires from pin 2, 3, 4, or 6 to the ground, you'll see a message showing which pin has been set low. By forcing an I/O pin to logic low, its corresponding bit in the register (a memory location) is set low as well. Since a program can PEEK into a memory location and check its contents, software can be written to detect the states (on or off) present at the control port, then proceed accordingly. In Program 2-1, your computer is sensing which pin you're setting low (by touching the wire from the pin to ground). Then it's taking this input and processing it; in this case it's used to print out messages. The next chapter will use this infor- mation to construct a useful input device, a joystick. 20 B CHAPTER 3 ■ " Making a Joystick Making a Joystick It may seem that a joystick, with its molded plas- tic parts, would be impossible to make at home. Open a Commodore or Atari joystick, though, and you'll see that it's not that complex. In fact, it only contains five switches. Four of the joystick's switches are used to detect the direction the control stick is pushed. The fifth acts as a fire button. A switch is pressed if the joy- stick is moved up, down, left, or right. If the stick is moved diagonally, two switches are pressed. Moving the stick diagonally up and to the right, for example, presses both the "up" and "right" switches. These switches are used to make the connection between one of the five input lines (pins 1, 2, 3, 4, and 6) of the control port and the ground (pin 8). Instead of your touching wires together, as you did while experimenting with the control port, switches are closed to make the connections. Since a joystick is basically a set of switches, you can make your own version of this device. In your first joystick, four push button switches are substituted for the control stick. The four buttons correspond to the directions a joystick can indi- cate — up, down, left, and right. To get diagonal directions, you'll press two buttons, the top and right buttons to indicate a move upward and to- ward the right, for instance. The fire button is a fifth push button switch and functions just as does its counterpart on a commerical joystick. As you can imagine, the push button joystick works better with some programs than with others. The push button joystick lets you move with greater control in games and in applications where 23 CHAPTER 3 movement in the four main directions is required. Applications or games requiring diagonal moves, however, are trickier than with a standard joystick. To make a push button joystick for your Com- modore or Atari computer, you'll need the follow- ing parts: Part Quantity Part Number 5 Momentary contact normally open switches 275-1547 1 Plastic case 270-231 1 9-pin D-subminiature female 276-1538 You'll also need some stranded copper wire or ribbon cable. 1. Cut six pieces of wire about 24 inches long. Remove about 1/4 inch of insulation from each end. Solder wires to pins 1, 2, 3, 4, 6, and 8 of the 9-pin plug. 2. Remove the cover from the plastic case and drill five holes for the switches (Figure 3-1). 3. Mount a switch in each of these holes. 4. Drill a hole in the top end (the end closest to the up switch) of the plastic case for the wires from the connector. 5. Pull the six wires from the 9-pin plug through the hole you just drilled, and about 10 centi- meters from their ends, tie them in a knot so that they can't be pulled back through the hole. 6. Solder the wire from pin 8 to one of the termi- nals of a switch (probably the up switch, since it's closest to the hole you drilled in the top side of the cover). Using several small lengths of wire, connect this terminal to a terminal of each of the other four switches in a jumper fashion (Figure 3-2). 24 Making a Joystick Figure 3-1 . Drilling the Cover Up Fire ( I This front view of the plastic case shows the approximate posi- tions where you should drill the five holes for the joystick's button switches. 7. Take the wire from pin 1 of the plug and sol- der it to the free terminal of the up switch (see Figure 3-2 for a layout view, or Figure 3-3 for a schematic view). 8. Solder the wire from pin 2 to the free terminal of the down switch. 9. Solder the wire from pins 3, 4, and 6 to the free terminals of the left, right, and fire switches respectively. 10. Replace the cover of the plastic case. Your joy- stick is complete. 25 CHAPTER 3 In this back view of the joystick cover, you can see how the switches are wired. Notice that the wire from pin 8 of the 9-pin connector is first connected to the up switch, then shorter pieces of wire are used to connect a terminal on each of the other four switches. Making a Joystick Figure 3-3. Joystick Schematic Pin 1 Pin 2 Pin 3 Pin 4 Pin 6 "A Up switch I / -O r 1 Down switch I / 1 Left switch 1 Right switch Fire button To pin 8 of 9-pin plug Schematic view of the push button joystick wiring. Figure 3-4. The Finished Push Button Joystick The completed push button joystick looks like this. Five buttons appear on the top of the finished case (above), while the wiring can be clearly seen in the view from the bottom (below). CHAPTER 3 A Gravity Joystick You can also use other types of switches to make a joystick. One alternative is to use tilt switches in place of the four directional push button switches. A tilt switch is a switch which closes only when it's tilted in the proper direction. One type of tilt switch consists of a plastic case with a metal ball inside. When the case is held at the proper angle, gravity causes the ball to roll to one side, where it touches both terminals of the switch, closing the contact. Some tilt switches use liquid mercury in place of the metal ball. If you're using tilt switches, be sure to mount them inside the plastic case of your joystick to prevent them from breaking. Warning: This is especially important if you're using mercury switches. Mercury is a potential health hazard. The switches can be glued to the inside of the case using epoxy and should be mounted so that they close (turn on) when the joystick is tilted in the proper direction. This means the right switch should close when the case is tilted to the right, the left switch should close when the case is tilted left, and so on. You tilt the gravity joystick in the direction you would normally push the control stick if you were using an ordinary joystick. Because of its unique feel, the gravity joystick adds another dimension to game playing. While moving objects on the screen is easy, keeping them stationary requires steady hands. Your joystick, whether push button or tilt switch, will work with any programs requiring a joystick. In fact, you may want to try making your own custom controller, perhaps something as un- usual as a steering wheel for a racing game. Making a Joystick Figure 3-5. Inside a Gravity Joystick The gravity joystick has only one button (the fire button), since it's operated by tilting it in the proper direction (above). Tilting the joystick case closes contacts within one or more of the mercury switches (below). CHAPTER 4 Game Paddles Game Paddles Game paddles can make arcade-style games like car racing simulations, tennis, and Ping-Pong more realistic and fun. Unlike joysticks, game pad- dles are analog devices. While joysticks provide the computer with either on or off signals, paddles provide the computer with a varying signal. A paddle contains a resistor with a variable amount of resistance and a switch in one case. The switch acts as the fire button and operates like the fire button on a joystick. The electrical re- sistance of the paddle depends on the position of the variable resistor, often referred to as a poten- tiometer, or pot. When the pot is turned all the way in one direction, the resistance measured be- tween the potentiometer's side and middle leads is ohms. When the shaft is turned in the opposite direction, the resistance is about 500K ohms on Commodore paddles. Atari paddles require a resis- tance of about 1M (1 million) ohms. When paddles are used, current from the com- puter flows through the potentiometers. The amount of current that flows depends on the resis- tance in the pot. The greater the resistance, the less current flow. The opposite is also true — the less the resistance, the greater the current flow. By turning the knob of the potentiometer, the voltage, measured across the leads of the poten- tiometer, varies between volts (ground) and +5 volts. The computer senses this voltage and uses it to determine a value for the position of the potentiometer. This voltage, which is an analog value, must be converted to a digital value to be used by your computer. Analog-to-digital converters, sometimes called A/D converters, were once very expensive. 33 Fortunately, your computer has this hardware built in. Using its analog-to-digital converter, your computer interprets the voltage across the variable resistor of the paddle as a number between and 255 (1 to 228 for the Atari). This value is kept in special memory locations in your computer. For the Commodore 64 and 128, these memory loca- tions are 54297 and 54298 ($D419 and $D41A in hexadecimal). In the VIC-20, locations 36872 and 36873 ($9008 and $9009) are used. For the Atari computers, it's not necessary to PEEK the actual memory locations — Atari BASIC has a command, PADDLE(X), which lets you see the values re- turned for the paddle positions. The value of X in this Atari statement is or 1 (a different X for each paddle), provided the paddles are plugged into control port 1 . To build your own pair of game paddles, you'll need the following parts: Part Quantity Part Number 2 Plastic cases 270-231 2 Momentary contact switches 275-1566 1 9-pin D-subminiature female 276-1538 2 Plastic knobs 274-407 2 500K potentiometers 271-210 (Commodore) or 2 1M potentiometers (Atari) 271-211 You'll also need some ribbon cable or stranded copper wire to connect your paddles to your computer. Here's how to put your game paddles together: 1. Cut eight pieces of stranded copper wire about 24 inches long and remove about 1 /4 inch of insulation from each end. Game Paddles 2. Connect one end of two of the wires to pin 7 of the 9-pin plug. 3. Connect another two wires to pin 8 of the plug. 4. Solder the remaining four wires to pins 3, 4, 5, and 9. 5. Remove the cover from one of the plastic boxes and drill two holes as in Figure 4-1. One hole is for the potentiometer, while the other is for the switch. Drill a hole in one end of the plastic case for the wires. Repeat these steps for the second plastic box. 6. Mount the switches and potentiometers in their respective holes. Attach the knobs to the shafts of the potentiometers. 7. Take one wire from pin 7, one wire from pin 8, the wire from pin 3, and the wire from pin 9 of the 9-pin plug to one of the paddle boxes. Pull the wires through the hole in the top end of the box. Turn the box cover with the potentiometer and switch mounted on it over so that their leads are facing up (as shown in Figure 4-1). 8. Connect the wire from pin 8 to one lead of the switch. Solder the wire from pin 3 to the other switch lead. The wire from pin 7 should be sol- dered to the left side lead of the potentiometer, and the wire from pin 9 is connected to the middle lead of the potentiometer. Mount the cover on the box. One paddle is completed. 9. The procedure for the second paddle is identi- cal, except the wires are from pins 7, 8, 4, and 5 of the 9-pin plug. The wire from pin 8 connects to one lead of the switch. The other switch lead is connected to the wire from pin 4. The wire from pin 7 connects to the left lead of the potentiometer, and the remaining wire, from pin 5, connects to the middle lead. Close the plastic box, and your second paddle is finished. 35 CHAPTER 4 Game Paddles 3 -J2 .0) u_ .c 1 o o e "O <D -c o D •8 1 o ^ Q. * ®£ £ R o ^ <d 1 .o £ ■£ ° o -c c c ?=-£ 3 o S of t: C r- 0> CHAPTER 4 Figure 4-3. Under the Paddle If you've correctly drilled holes, placed components, and wired leads, the bottom view of the game paddle case should look something like this. To try out your paddles, turn off your computer and plug the paddles' 9-pin connector into control port 1. Turn on the computer, then type in and run the appropriate version of Program 4-1. Program 4-1 — Commodore 64/128 EF 10 POKE5 6333,127 : REM IRQ OFF HH 20 P0KE56322, 192 :REM SET BITS 6,7 OF { SPACE } DATA DIRECTION REGISTER FOR OUTPUT EC 30 POKE56320 , 64 : REM 128 FOR PORT 2 HG 40 X=PEEK( 54297 ) DJ 50 Y=PEEK( 54298) XE 60 POKE56322,255:POKE56333,129:REM RE STORE REGISTERS DG 80 PRINTX,Y SJ 100 GOTO10 38 Game Paddles Program 4-1 — VIC-20 GD 10 PRINT1-(PEEK(37151)AND16)/16;PEEK( 36872); RG 20 POKE37154, 127 :PRINT1- ( PEEK ( 37 152 ) A ND128)/128; : P0KE3 7 154 , 2 55 PS 50 PRINTPEEK( 36873 ) BD 60 GOTO10 Program 4-1 — Atari 10 PRINT PADDLE(O);" ";PADDLE(1) 20 GOTO 10 When you run the appropriate program, two columns of numbers should appear on the screen. Each column of numbers corresponds with a pad- dle. As you turn the knobs of the paddles, the numbers should vary between and 255 for the Commodore computers, and between 1 and 228 for an Atari computer. Several steps are necessary to read the paddles with a Commodore 64 computer. Since the key- board can interfere with values read at address 56321 ($DC01), it's necessary to turn off the IRQ (Interrupt Request). This prevents normal system processing from occurring. Program 4-1 does this in line 10. Bits 6 and 7 of the data direction register must be set up for output by setting the proper bits in address 56322 ($DC02). You want to place a 1 in bits 7 and 6 of 56322 for data direction register A. (The decimal equivalent 192 of the binary number 11000000 in line 20 sets bits 6 and 7 for output.) Line 30 stores the value 64 in the data port reg- ister A to select reading the paddles at port 1. (To read port 2, change the 64 in line 30 to 128.) Lines 40 and 50 PEEK the game paddle POTX and POTY locations, storing the proper values in the variables X and Y. the variables X and Y. 39 CHAPTER 4 Line 60 restores the IRQ and keyboard. Line 80 prints the values of X and Y to the screen. Since it's necessary to turn off the keyboard for input to the paddle registers, it's often best to read the values with a machine language (ML) routine. Figure 4-4. Paddles Done Both game paddles are wired to one 9-pin connector. The following ML routine (Program 4-2) works only on the Commodore 64 or Commodore 128 in 64 mode. The routine is POKEd into the cassette buffer and can be called by typing SYS 828 any- time you want to read the paddles. It's a simple matter to incorporate this routine's BASIC loader (omit line 40) into any program you write which requires paddle reading. To read a paddle value after calling the routine with SYS 828, simply PEEK the appropriate location: 40 Game Paddles Port 1 Paddle to Read Location to PEEK X 251 Y 253 Port 2 X Y 252 254 Program 4-2. ML Paddle Reader MF 10 1=828 :AD=251 HG 20 READ A: IF A=256 THEN40 RG 30 POKE I,A:I=I+1:GOTO20 QA 40 SYS 828 :PRINTPEEK(AD) ;PEEK(AD+1) ; P EEK( AD+2 ) ;PEEK(AD+3 ) :GOTO40 RF 50 DATA 76,63,3,162,1,120,173 KH 60 DATA 2,220,133,167,169,192,141 SX 70 DATA 2,220,169,128,141,0,220 EE 80 DATA 160,128,234,136,16,252,173 DS 90 DATA 25,212,149,251,173,26,212 CD 100 DATA 149,253,169,64,202,16,232 FP 110 DATA 165,167,141,2,220,88,96,256 41 1 CHAPTER 5 ■ An Analog Light Sensor An Analog Light Sensor Sometimes it's handy to be able to detect different intensities of light. Perhaps you'd like to have a simple switch to turn on your outside lights at dusk and then turn them off again at dawn. If you need to detect different degrees of lighting, you need an analog light sensor. The analog light sensor built in this chapter is a cadmium sulfide photocell. It's a variable resistor whose resistance changes proportionally to the amount of light which strikes its light-sensitive surface. This, in turn, provides the computer with information regarding just how much light is present. The resistance increases as the amount of light striking it decreases. Exposed to bright light, the cadmium sulfide photocell has a resistance of a few hundred ohms between its terminals. In darkness, this resistance increases to approximately 0.5 megohms — about the same value range as the potentiometer on the Commodore paddles. In fact, it's possible to connect the cadmium photocell in much the same manner as a paddle. Light Sensor — Commodore Computers To build an analog light sensor for a Commodore 64, Commodore 128, or VIC-20, you'll need the following parts: 45 Part Quantity Part Number 1 Cadmium sulfide photocell 276-116 1 9-pin D-subminiature female 276-1538 1 0.1 microfarad capacitor 272-1069 1 IK ohm resistor 271-8023 1 Solderless breadboard 276-175 You'll also need some stranded copper wire, as well as some solid copper wire (Radio Shack part number 278-1306). To complete the project, follow these steps: 1. Cut two pieces of the stranded copper wire about 24 inches long and strip about 1/4 inch of insulation from each end. Cut several small pieces of solid wire about 2 inches long to use as jumpers. (You'll need them in this circuit and most others in this book.) 2. Solder the end of one wire to pin 7, and the other wire to pin 9 of the 9-pin plug. 3. Connect the wire attached to pin 7, the +5 -volt lead, to point XI on the solderless breadboard. Place the other wire (that attached to pin 9) to point Yl on the board. 4. Install jumper wires between points Y2 and J2, points X2 and A2, and points J13 and Y13. 5. Place the 0.1 microfarad capacitor between points F2 and E2. 6. Bend the leads of the IK ohm resistor, and in- stall it between points B2 and B13. 7. Install the cadmium sulfide photocell between points E13 and F13. An Analog Light Sensor Figure 5-1 . Schematic Drawing of Analog Photocell (Commodore) Pin 7 +5v R i Rj l.OKfl Cadmium sulfide photocell Cj 0.1|if Building an analog light sensor for a Commodore personal com- puter requires several parts, including a cadmium sulfide photo- cell, a resistor, and a capacitor. Light Sensor — Atari Putting together an analog light sensor for the Atari computer series involves some different components and different directions. You'll need: Part Quantity Part Number 1 Cadmium sulfide photocell 276-116 1 9-pin D-subminiature female 276-1538 1 1M potentiometer 271-211 1 Solderless breadboard 276-175 You'll also need some stranded copper wire as well as some solid copper wire. 47 CHAPTER 5 Figure 5-2. Breadboard Layout for Atari Analog Photocell 1 2 3 4 5 6 7 » • X2 9 10 11 12 13 14 15 A B C D E F G H I J A2 B2 Cadmium sensor B6 Y2 • E6 jjf IM pot * F6 J6 Y6 The breadboard for the Atari version of the analog light sensor clearly shows where each component and jumper should be placed. 1. Cut two pieces of the stranded copper wire about 24 inches long and strip about 1/4 inch of insulation from each end. Cut several small pieces of solid wire about 2 inches long to use as jumpers. 2. Solder the end of one wire to pin 7, and the other wire to pin 9 of the 9-pin plug. 3. Connect the wire attached to pin 7 , the +5 -volt lead, to point XI on the solderless breadboard. Place the other wire (that attached to pin 9) to point Y2 on the board. 4. Install jumper wires between points Y6 and J6, and points X2 and A2. 5. Place the IM potentiometer between points E6 and F6. 6. Install the cadmium sulfide photocell between points B2 and B6. 48 An Analog Light Sensor To see how your analog light sensor works, use Program 4-1 from the previous chapter. If you're using a Commodore 64, or a Commodore 128 in 64 mode, you can use Program 5-1 below instead. If you have an Atari computer, enter and run the two-line program you see below. For a Commo- dore 64 or 128, the light sensor should be plugged into port 2. Plug the Atari light sensor into port 1. Program 5-1 — Commodore 64/128 AD 10 1=828 PE 20 READ A: IF A=256 THEN 50 RG 30 POKE I,A:I=I+1:GOTO20 FX 40 REM ANALOG LIGHT METER GH 50 SYS 828:A=PEEK(25 2) DH 60 IFB=ATHEN50 GX 70 B=A: PRINT " {CLRjLIGHT LEVEL IS NOW" ;A DG 80 GOTO50 KA 90 DATA 76,63,3,162,1,120,173 FR 100 DATA 2,220,133,167,169,192,141 BJ 110 DATA 2,220,169,128,141,0,220 QG 120 DATA 160,128,234,136,16,252,173 QE 130 DATA 25,212,149,251,173,26,212 CS 140 DATA 149,253,169,64,202,16,232 FJ 150 DATA 165,167,141,2,220,88,96,256 Program 5-1 — Atari 10 PRINT PADDLE(O) 20 GOTO 10 When the you run the program, numbers in the range 0-255 (1-228 for the Atari) will scroll on your screen. These numbers are related to the amount of light which is falling on the photocell. To see this, try reducing the light reaching the photocell by covering it with your hand. As you do, the numbers in the column will increase. Con- versely, increasing the amount of light which hits the photocell, perhaps by shining a flashlight on it or by holding it closer to a lamp, causes the num- bers on the screen to decrease. 49 CHAPTER 5 Note: On the Commodore light sensor, you may need to adjust the value of Rl, the IK ohm resis- tor, to cause a swing through the entire range of values. In other words, you may need to use a dif- ferent resistor, one rated higher or lower than IK. Just experiment until you find the proper value for your application. That's part of the fun in breadboarding — making changes is easy. The computer treats the light sensor as though it were a game paddle. The varying resistance of the sensor provides the computer with a signal be- tween volts and +5 volts at its port. The voltage is converted to a digit between and 255 by the analog-to-digital converter in your computer. This value is stored in a memory location, where it can be read by a program. It shouldn't be hard, once you have the sensor built, to take this information and develop a light meter program which will de- termine the degree of light present at the sensor. jl Two analog light sensors can be connected to your computer through the single 9-pin plug (just like two game paddles). The second photocell is at- tached between pins 7 and 5 of the 9-pin plug. To read the value of this second sensor, simply PEEK memory location 54298 ($D41A) for the Commo- dore 64/128, or PEEK location 36873 ($9009) for the VIC. Don't forget to set the data direction reg- isters for output. The BASIC command PAD- DLE(l) can be used to read this value for Atari computers. 50 CHAPTER 6 A Light Pen A Light Pen A light pen is a fascinating input device. By point- ing a light pen at the computer's screen and press- ing its input button, you can make selections from a menu, draw a picture, or perform whatever function the computer program you're using al- lows. The biggest attraction of a program which uses a light pen is that you don't have to use the keyboard — using a program becomes as simple as pointing. To understand how a light pen works, you must know a bit about how your computer's monitor displays a picture. Pictures on the screen are made up of tiny dots of light. These dots are produced from an electron gun in the monitor which shoots electrons at the screen. These electrons excite the phosphor coating on the screen, causing it to emit light. In this way, the electron gun actually "paints" the picture, dot by dot, row by row, until the screen is filled. All of this is done in a fraction of a second and is updated many times every second. Your computer keeps track of where the beam of electrons from the electron gun is at all times. The light pen, when pointed to a spot on the screen, triggers the computer to store the location of the beam as it passes. These x and y coordi- nates are placed in special registers of your com- puter. Since the position of the beam stored is the same as that of the light pen, programs can deter- mine where you're pointing the light pen by checking the values contained in these registers. The program can then use this information to per- form various functions, like drawing a line or se- lecting an option. 53 CHAPTER 6 Here's what you'll need to make a simple light pen: Part Quantity Part Number 1 Solderless breadboard 276-175 1 7400 quad 2-input NAND 276-1801 gate IC 1 TIL infrared phototransistor 276-145 1 IK ohm resistor 271-8023 (Commodore only) 1 9-pin D-subminiature female 276-1538 1 Push button microswitch 275-016 (normally open) You'll also need some stranded copper wire, a ballpoin t pen, and some solid copper wire. When building the light pen, refer to Figure 6-1, the schematic drawing for the light pen circuit, and Figure 6-2, the solderless breadboard layout, as you follow these instructions: 1. Solder lengths of solid copper wire to pins 6, 7, and 8 of the 9-pin plug. These wires will connect the plug with the solderless breadboard. 2. Insert the wire from pin 6 to point El of the breadboard, the wire from pin 7 to point Yl, and the wire from pin 8 to point XI. 3. Insert the 7400 IC in the breadboard so that its pin 1 is at point E16 and its pin 8 at point F10. You can tell which pin of the IC is pin 1 by one of two methods: Pin 1 may have a circle indented in the plastic beside it. Alternatively, there may be a semicircular indention at the end of the IC where pin 1 is located. In this case, pin 1 is the first pin in a counterclock- wise direction from this indention (looking at the top of the IC). In either case, the remain - 54 A Light Pen ing pins are numbered counterclockwise around the IC. 4. Insert five solid copper jumper wires as follows: First Second Wire Location Location 1 A10 X10 2 A12 A13 3 C13 D14 4 C15 D16 5 J16 Y16 5. Remove the ink cartridge from the ballpoint pen. The barrel of the pen will act as the body of your light pen. With your hot soldering iron, carefully melt a small hole at the end of the barrel where the ballpoint used to be for the wires. Warning: Be sure to clean off the tip of your sol- dering iron when you're finished. If you intend to use your soldering iron for serious work, it's a good idea to change the tip of your iron after using it to melt plastic. Substances from the burn- ing plastic will adhere to the tip of your iron, making it unsuitable for serious soldering work. [We found that it wasn't necessary to burn a hole for installing the TIL 414 phototransistor when we used a BIC ballpoint pen — Editor.] 6. Cut four pieces of stranded copper wire about 30 inches long to connect your light pen with the solderless breadboard. These wires must be long enough to allow you to move the light pen freely. 7. Solder one of the four wires to the emitter lead of the phototransistor. Another wire should be soldered to its collector lead. Attach a small piece of electrical insulation tape around both the collector and emitter leads so that they won't come in contact and short out. 55 CHAPTER 6 OS AAAA PS 5 c > o Q O o E © o co c © O- O) -o © 00 D O > + IN c Oh 6 Q 6b en S •< 2 7 o s a T3 S 5 — 3 "* § cd S s g H S I a ok io a O G. H 1/5 ft, tfi r-t C Oh o -C o A Light Pen CHAPTER 6 8. Pull the wires of the phototransistor through the pen barrel and glue the phototransistor in place at the "tip" end. Be careful not to get any glue over the phototransistor's light-sensitive part. Figure 6-3. In Reality — The Light Pen Breadboard 'il'iXiiQift-..- '-'AM I Wl: -^&M : M^ ■ Schematics and layouts aside, this is how your light pen solderless breadboard should look when you're finished. 9. The wire from the emitter plugs into position XI 6 of the solderless breadboard, while the wire from the collector inserts into point A16. 10. Solder the remaining two 30-inch wires to the leads of the microswitch. Pull the wires through the hole you melted and out the open end of the pen's barrel. Glue the microswitch to the barrel of the pen. 11. One of the wires from the switch inserts into point Al on the breadboard, while the other goes into point A2. 12. Insert the IK resistor between points C2 and Cll of the solderless breadboard. (For the Atari version of this circuit, use a jumper wire in place of the resistor.) 58 A Light Pen To check that your light pen is operating properly, turn off your computer and insert the 9-pin plug into control port 1 of the Commodore 64/128 and Atari computers. (The VIC has but one control port.) A light pen won't work in control port 2 of the Commodore 64 and 128 computers. Turn on your computer, type in, and run the appropriate version of Program 6-1. Program 6-1 — Commodore 64/1 28 5 A = 53267:B = 53268 10 PRINT "X=";PEEK(A),"Y=";PEEK(B) 20 GOTO 10 Program 6-1— VIC-20 5 A = 36870:B = 36871 10 PRINT "X = ";PEEK(A),"Y = ";PEEK(B) 20 GOTO 10 Program 6-1 — Atari 5 A = 564:B = 565 10 PRINT "X=";PEEK(A),"Y=";PEEK(B) 20 GOTO 10 Move your light pen around the screen while pressing the microswitch. The numbers of the two columns should change, giving you the coordi- nates of the point of your light pen. Warning: You may have to adjust the brightness of your monitor to get your light pen to work properly. How It Works Your computer is set up to store the position of the electron beam every time pin 6 of the control port, normally at a logic high state, is set low. The light pen circuit is designed to set this pin low. This triggers the computer to save the electron beam's position when it passes the light pen. 59 CHAPTER 6 The phototransistor acts as a very fast switch. Normally, the path between the emitter and col- lector of the phototransistor is like that of an open switch. The moment the beam of the electron gun passes the point at which the phototransistor is aimed, enough light is emitted to turn the transis- tor on. When this happens, the connection be- tween the emitter and the collector of this device is effectively that of a closed switch. Since the emitter is connected to ground, the inputs of the NAND gate, which are attached to the collector, are grounded as well. The operation of NAND gates and other logic building blocks is explained in greater detail in Chapter 10, "Digital Logic." Let it suffice to say here that the two NAND gates used in the light pen circuit act as a noninverting buffer. Non- inverting buffers are used when a signal isn't suf- ficient to drive the inputs of other IC gates. The output of this type of buffer is the same as its input. The output of the buffer is connected to pin 6 of the control port through a resistor and the push button switch. When the push button switch is open, the light pen circuit is disconnected from pin 6 of the control port. The push button switch must thus be pressed if this pin is to be triggered. When the light pen is aimed at a point on the screen and the button is pressed, several things happen. Because the screen picture is refreshed many times each second, the electron beam passes the phototransistor at least once in the time it takes to press and release the button. Before and after the beam passes the phototransistor, the in- put and output of the buffer are logic high, and as a result, pin 6 remains at that state. The moment the beam passes the phototransitor, the input and output of the NAND gate buffer are set low. Thus, 60 A. Light Pen pin 6 of the control port is set low for a fraction of a second, long enough to trigger the computer to store the location of the electron beam. Figure 6-4. The Completed Light Pen The entire light pen system, comprised of the breadboard, the ink-pen-based light pen, and the 9-pin connector, can be used for a multitude of programming applications, from drawing pro- grams to menu selection. Programming with the Light Pen As you ran the test program, you probably noticed that when the pen was held at one spot, the co- ordinate numbers didn't remain constant, but in- stead stayed within a relatively small range. This must be taken into account when writing pro- grams to work with your light pen. Another point to remember is that once you use the light pen, the values remain the same in their registers until the light pen is used again. This means your program should have a way of check- ing that the values in the register are a new selec- tion rather than a previous selection. For instance, suppose the registers contain the values 120 and 61 CHAPTER 6 125 from a previous menu selection. When you put up your next menu, you expect the user to make another selection with the light pen. In or- der to determine where the light pen is pointed, you might compare the register values to a speci- fied coordinate range. If the range includes one of the values from the previous selection, the pro- gram would immediately proceed as if the pen is pointed in this range before the user even has a chance to use the light pen. One way to avoid this problem is to check whether the user has pressed the push button again. This insures that the previous values in the register have no effect on the selection. Since the light pen line (pin 6) is the same as that of the fire button, you can check for it the same way you would check for the fire button. Another way to avoid this problem is to make sure two consecu- tive menus have no ranges in common. Try entering and running the appropriate version of Progam 6-2, which shows how a light pen can be used to make selections from a menu. When the menu appears, just point to the asterisk (*) be- side your choice and press the microswitch. The screen clears and the choice you made appears. After a short delay, the word CONTINUE is dis- played with an asterisk in front of it. Point your light pen to the asterisk and press the microswitch to return to the menu. Program 6-2 — Commodore 64/1 28 QK 100 REM * LIGHT PEN DEMO * HA 150 AS=CHR$(147) :PRINTA$ BB 160 PRINTTAB ( 10 ) "THREE CHOICES" MQ 170 PRINT: PRINT GJ 180 PRINTTAB ( 5 ) " * CHOICE ONE " GF 190 PRINT: PRINT: PRINT: PRINT DA 200 PRINTTAB (5 ) "* CHOICE TWO" RC 210 PRINT: PRINT: PRINT: PRINT FK 220 PRINTTAB ( 5 ) "* CHOICE THREE" A Light Pen DD 230 A=PEEK(53267) : B=PEEK ( 53 268 ) FJ 240 IF A>55 THEN 230 EB 250 IF (B>70) AND (B<80) THEN 300 HG 260 IF (B>110) AND (B<120) THEN 330 XP 270 IF (B>150) AND (B<160) THEN 360 HF 290 GOTO230 RF 300 PRINTA? DA 310 PRINT "CHOICE ONE " BF 320 GOTO 400 KH 330 PRI NTA$ GD 340 PRINT "CHOICE TWO" RJ 350 GOTO 400 FK 360 PRINTA$ QS 370 PRINT "CHOICE THREE" KS 400 FOR 1=0 TO 1500 XP 410 NEXT I: PRINT CB 420 PRINT"* CONTINUE" AS 430 IF PEEK( 53267) <55 AND PEEK(53268) <7012 SPACES jTHEN 150 KX 440 GOTO 430 Program 6-2— VIC-20 XF 10 A$=CHR$ ( 147 ) rPRINTA? JK 20 PRINTTAB(4) "THREE CHOICES" CE 30 PRINT: PRINT BQ 40 PRINTTAB ( 5 ) " * CHOICE ONE" CF 50 PRINT .-PRINT .-PRINT .-PRINT HF 60 PRINTTAB (5)"* CHOICE TWO " JC 70 PRINT: PRINT: PRINT: PRINT FG 80 PRINTTAB ( 5) "* CHOICE THREE" RH 90 A=PEEK(36870) : B=PEEK ( 36871 ) CA 100 IF A>65 OR A<40 THEN90 QQ 110 IF (B>30) AND (B<40) THEN150 DH 120 IF (B>50) AND (B<60) THEN180 HJ 130 IF (B>70) AND (B<80) THEN210 SX 140 GOTO90 MQ 150 PRINTA$ CK 160 PRINT "CHOICE ONE" BR 170 GOTO230 GS 180 PRINTA$ HP 190 PRINT "CHOICE TWO" AS 200 GOTO2 30 HX 210 PRINTA$ XE 220 PRINT "CHOICE THREE" DF 230 FOR 1=0 TO 1500 GS 240 NEXT I: PRINT 63 CHAPTER 6 DP 250 PRINT"* CONTINUE" QD 260 IF PEEK( 36870 ) <40 AND PEEK( 36871) <40{2 SPACES } THEN1 CF 270 GOTO260 Program 6-2 — Atari PF 100 REM LIGHT PEN DEMO AN 150 PRINT CHR* (125) NO 160 PRINT " THREE CHOICES" LD 1 70 PRINT : PR INT .-PRINT CB 180 PRINT "* CHOICE ONE" LF 1 90 PRINT :PRINT :PRINT DC 200 PRINT "* CHOICE TWO " KO 210 PRINT :PRINT .-PRINT LC 220 PRINT "* CHOICE THREE PH 230 A=PEEK (564) : B=PEEK (565) NB 240 IF A>90 THEN 230 CK 250 IF (B >25) AND (B<35) THEN 300 DC 260 IF (B >45) AND (B<55) THEN 330 DA 270 IF (B>60) AND (B<70) THEN 360 BJ 290 BOTO 230 AK 300 PRINT CHR* (125) PC 310 PRINT "CHOICE ONE " BC 320 BOTO 400 AN 330 PRINT CHR* (125) AN 340 PRINT "CHOICE TWO " BF 350 BOTO 400 BA 360 PRINT CHR* (125) 10 370 PRINT "CHOICE THREE" ME 400 FOR I =1 TD 15:PRINT : NEXT I CC 410 PRINT PG 420 PRINT "* CONTINUE" DE 430 IF PEEK ( 564 ) < 90 AND PEEK(565) >B0 THEN 150 SI 440 BOTO 430 64 CHAPTER 7 A Digital Light Sensor A Digital Light Sensor The light pen you built in Chapter 6 is a type of light sensor — it detects light from the computer's screen and sends out an appropriate signal. But what if you want to be able to tell whether it's dark outside, or whether somebody opened your closet door (letting light inside)? Or perhaps you want to build an electronic timer that starts and stops timing when a beam of light is broken? To detect different levels of light, you need a slightly more complex sensor. This chapter will show you how to build and use a variable digital light sensor. This sensor pro- vides the computer with either a high (1) or low (0) digital signal. When the light sensor is adjusted for a certain level of light, the computer receives a logic low (0) signal as long as this level of light, or more, is maintained. However, if the level of light falls below this setting, the computer gets a logic high (1) signal from the sensor. This type of sen- sor is useful for applications such as light beam timers and counters, two applications which will be demonstrated here as well. To build the digital light sensor, you need these parts: Part Quantity Part Number 1 3900 op amp IC 276-1713 1 500K potentiometer 271-210 (Commodore) 1 1M potentiometer 271-211 (Atari) 1 100K ohm resistor 271-8045 67 CHAPTER 7 Part Quantity Part Number 1 10K ohm resistor 217-8034 1 IK ohm resistor 271-8023 1 TIL 414 infrared photo- 276-130 transistor 1 9-pin D-subminiature female 276-1538 1 Solderless breadboard 276-175 You'll also need some solid copper wire for jumper connections and some stranded copper wire for connections to the phototransistor. These steps will take you through the process of building your digital light sensor: 1. Cut three pieces of solid copper wire and re- move about 1 /4 inch of insulation from each end. 2. Connect one wire each to pins 1, 7, and 8 of the 9 -pin plug. 3. Connect the wire from pin 8 to location XI of the solderless breadboard. 4. Connect the wire from pin 7 to location Yl. 5. Connect the wire from pin 1 to location F5. 6. Plug the 3900 op amp IC into the solderless breadboard so that pin 1 goes to point El 5, and pin 8 goes to point F9. 7. Cut two pieces of solid copper wire about 2 inches long and remove about 1 /4 inch of insu- lation from each end. Solder one wire to an out- side lead of the potentiometer. Solder the other wire to the middle lead of the potentiometer. 8. The wire from the outside lead connects to point X22 of the solderless breadboard. The wire from the potentiometer's middle lead connects to point A22. 68 A Digital Light Sensor 9. Cut two pieces of stranded copper wire about 12 inches long and remove about 1/4 inch of insulation from each end. Solder one wire to the emitter of the phototransistor and the other wire to the collector. 10. The wire from the collector plugs into point Y22 of the solderless breadboard, while the wire from the emitter inserts into point J22. 11. Insert the resistors as follows on the solderless breadboard: Resistor From To IK ohm B4 J4 10K ohm B22 B13 lOOKohm D13 D12 12. Connect five solid copper wire jumpers on the solderless breadboard as follows: Jumper From To 1 E22 F22 2 Y15 J15 3 X14 A14 4 C12 C4 5 X9 A9 Figure 7-1 . The Final Sensor Board Your final light sensor breadboard will look like this. 69 CHAPTER 7 A Digital Light Sensor CHAPTER 7 Inside the Sensor The phototransistor in this circuit acts as a switch. It's in series with the 500K potentiometer. When light strikes the light-sensitive surface, current will flow through the emitter-collector junction. The sensitivity is set by adjusting the 500K ohm poten- tiometer in series with the phototransistor. The operational amplifier's (op amp) inverting input is connected between the potentiometer and the phototransistor. The voltage at the op amp's input is determined by the resistances of the potentiom- eter and phototransistor. The op amp is set up using the 10K ohm and 100K ohm resistors so that when the input voltage is a certain level, its output goes to the logic low level. The output of the op amp is connected to pin 1 of the control port through a IK ohm resistor. The phototransistor must be set for the desired level of light. This is done by aiming the light- sensitive part of the phototransistor at a light source, then adjusting the potentiometer for trig- gering at the desired light level. Program 7-1 pro- vides the necessary lines for testing and adjusting this circuit. Adjust the potentiometer so that the output to the computer turns logic low. Once this is done, if the phototransistor receives less light, the input voltage of the op amp no longer will be the cor- rect voltage to force its output low. As a result, pin 1 of the 9-pin plug returns to its normal logic high level. Putting It to Use To use the light sensor, first turn off your com- puter. Insert the 9-pin plug into port 2 of the Commodore 64 or 128 (there's only one port on 72 A Digital Light Sensor the VIC), or into port 1 of any Atari computer. Turn your computer back on, type in, and run the version of Program 7-1 for your machine. For this demonstration, the sensor is set to the lighting in the room, so make sure that the light-sensitive portion of the phototransistor is uncovered and facing up. Program 7-1 — Commodore 64/128 JE 10 IFPEEK(56320)AND(2T0)THEN20 XR 15 PRINT " {CLRjLIGHT IS ON":GOTO10 EP 20 PRINT "{CLR} LIGHT IS OFF":GOTO10 Program 7-1— VIC-20 QD 10 IF(PEEK(37151) AND 4 ) THEN PRINT " {CLR} LIGHT IS OFF" AS 20 IF (PEEK( 37151 ) AND 4)=0THEN PRINT { SPACE }" {CLR} LIGHT IS ON" SB 30 GOTO10 Program 7-1 — Atari 10 IF STICK(0)=15 THEN PRINT "OFF" 20 IF STICK(0) = 14 THEN PRINT "ON " 30 GOTO 10 When you run the program, a column of mes- sages should appear on the screen. Either the mes- sage LIGHT IS ON or LIGHT IS OFF will be displayed. If the message is LIGHT IS ON, it means the sensor is detecting light at the level of or greater than the potentiometer setting. When the sensor detects the light level, it forces pin 1 of the control port low, just as connnecting it to pin 8 (ground) does. If the sensor does not detect the light level it's set for, pin 1 of the control port remains at logic high. Adjust the setting of the potentiometer by turning its shaft. Doing this controls the sensitivity of the light sensor. You should find a point as you turn 73 the potentiometer shaft where the messages in the column change from LIGHT IS OFF to LIGHT IS ON. In order to set the light sensor to detect the light in the room, leave the potentiometer set at the point where the messages just change from LIGHT IS OFF to LIGHT IS ON. Just as with a joystick, programs can check the control port for the light sensor's signal. All that's necessary is to PEEK the appropriate register, or use the STICK command in the case of the Atari, then check the bit (corresponding to pin 1, in this case) for a 1 or 0. A Digital Light Beam Timer This circuit, quite similar to the light sensor, can be used as a timer circuit for slot cars, or for any application involving measuring time over a dis- tance. This project is essentially the same as the digital light sensor circuit you just completed. The following parts are required: Part Quantity Part Number 1 3900 op amp IC 276-1713 I 500K potentiometer 271-210 (Commodore) 1 1M potentiometer 271-211 (Atari) 1 100K ohm resistor 271-8045 1 10K ohm resistor 217-8034 1 IK ohm resistor 271-8023 i Infrared emitting diode 276-142 l Infrared detecting diode 276-142 l 9-pin D-subminiature female 276-1538 l Solderless breadboard 276-175 You'll also need some solid copper wire and some stranded copper wire. A Digital Light Sensor CHAPTER 7 Construct the circuit as you did for the digital light sensor, but position the infrared emitting diode and the infrared detecting diode so that the emit- ting surface and detecting surface face each other. Tests indicate that the maximum usable distance between these diode pairs (the two parts come in one package, listed as Radio Shack part number 276-142) is less than one foot. Connect the infrared emitter's anode to the y line on the solderless breadboard, and the cathode to the x line. Use the appropriate version of Pro- gram 7-1 to adjust and focus the diodes so that the circuit triggers when the beam of light from the emitter is broken, not when ambient room light is interrupted. The light in the infrared is in- visible to the naked eye. You'll see no indication that the diode is turned on. Be sure you've in- stalled it correctly in the circuit. When you've tested the circuit and are satisfied that it's functioning properly, type in and run Pro- gram 7-2. Adjust the potentiometer as you did with the digital light sensor, then press the X key to continue the program. Start the timer by breaking the beam between the infrared emitting and infrared detecting di- odes. When the beam is broken a second time, the elapsed time is displayed and the timer stops. Press the X key to reset the timer and run the pro- gram again. This circuit could be useful as a burglar alarm, one that detects when an object or intruder breaks the beam of infrared light. Program 7-2 — Commodore 64/1 28 DX 110 REM TIMER PROGRAM MH 120 PRINT" ICLR} ADJUST THE INFRARED BE AM AND THE" FA 130 PRINT "POTENTIOMETER UNTIL THE MES SAGE JUST" /6 A Digital Light Sensor GQ 140 PRINT "CHANGES FROM OFF TO ON" MG 150 PRINT : PRINT "PRESS X TO CONTINUE I DOWN j " AQ 160 A$=CHR$(145)+CHR$(145) PM 165 A=PEEK( 56320) JM 170 IF (A AND 1) THEN PRINT "LIGHT IS OFF" GE 175 IF (A AND 1)=0 THEN PRINT "LIGHT I SPACE} IS ON " KE 180 GET B$ BQ 190 IF B$="X"THENGOTO220 DS 200 PRINTA$ AD 210 GOTO 165 HD 220 PRINT" I CLR] BREAK BEAM TO START TI MER" QX 230 IF (PEEK( 56320) AND 1)=0 THEN 230 DF 240 TI$="000000":PRINT"{CLR}TIMER STA RTED" MD 250 IF (PEEK(56320) AND 1) THEN 250 KH 260 IF (PEEK( 56320) AND 1)=0 THEN 260 RC 270 PRINT "TIME IS" ;TI/ 60; "SECONDS" XH 280 PRINT" {DOWN J PRESS X TO RESET TIME R" DG 290 GETB$ :IFB$=" "THEN290 CD 300 IFB$="X"THEN220 MK 310 GOTO290 Program 7-2— VIC-20 SH 10 PRINT" {CLR } ADJUST THE INFRARED {3 SPACES} BE AM AND THE CIRCUIT QS 20 PRINT "UNTIL THE MESSAGE JUST" SR 30 PRINT "CHANGES FROM OFF TO ON" KQ 40 PRINT: PRINT "PRESS X TO CONTINUE" GM 50 A$=CHR$(145) PB 60 A=PEEK( 37137 ) AE 70 IF (A AND 4) THEN PRINT "LIGHT IS { SPACE }OFF" PQ 80 IF (A AND 4)=0 THEN PRINT "LIGHT I S ON " XA 90 GET B$ MH 100 IF B$="X"THEN130 QB 110 PRINTA$A$ SQ 120 GOTO60 PH 130 PRINT "{CLR} BREAK BEAM TO START" RP 140 IF ( PEEK ( 37137 )AND4)=0 THEN140 KS 150 TI$="000000" RX 160 IF (PEEK (37 137) AND 4) THEN160 JD 170 IF (PEEK( 37137) AND 4)= THEN170 77 CHAPTER 7 MQ 180 PRINT "TIME IS " ; Tl/60 ; "SECONDS " HD 190 PRINT "PRESS X TO RESET TIMER" XA 200 GETG$:IFG$=""THEN200 QX 210 GOTO130 Program 7-2 — Atari AP110 REM TIMER PROBRAM KP 120 PRINT "TURN ON FLASHLIGHT AND ADJUST THE " LF 130 PRINT "POTENTIOMETER TILL THE MESSAGE JUST" KO 140 PRINT "CHANGES FROM OFF TO ON II FE 150 PRINT "PRESS X TO CONTINUE" GH 155 FOR J=l TO 2500:NEXT J KE 170 IF STICK<0>=15 THEN PRINT "OF F" BK 175 IF STICK(0>=14 THEN PRINT "ON II MB 180 REM CHECK IF X KEY PRESSED KI 190 IF PEEK<764)=22 THEN 215 SE210 GOTO 170 B6 212 REM CLEAR OUT PREVIOUS KEYSTR OKE 0ft215 POKE 764,255 JB 220 PRINT "BREAK BEAM TO START TI MER" IJ 230 IF STICK(0)=14 THEN 230 OA 240 POKE 1S,0:POKE 19,0:POKE 20,0 10 250 IF STICK(0)=15 THEN 250 IP 260 IF STICK<0)=14 THEN 260 BG 270 PRINT "TIME IS " ; < ( PEEK < 1 8 ) * 2 55*255) + (PEEK < 19) *255) + < PEEK ( 20) ) ) /60; " SECONDS" For something a little different, modify Program 7- 2 to count (COUNT = COUNT + 1) every time the beam is interrupted. 78 CHAPTER 8 An Electronic Switch An Electronic Switch So far, all the projects you've completed have been sensors — devices that transfer information about the outside world into your computer. But your computer can also be used to control outside devices through electronic signals. While exploring the control port, you saw how information in the form of electronic on/off sig- nals can be sent to your computer using the data (I/O) lines. These same wires can also be used by your computer to send digital signals out. Whether your computer is using the data lines for input or output, two registers are involved. The first register, called the data port, contains the actual data being transferred. The signal on each data line corresponds with a bit stored at this location. When receiving data, your program sim- ply checks the bit which corresponds to the af- fected I/O line. Suppose you wish to see whether pin 1 of control port 1 is set low, as it is if the joy- stick is pushed to the up position. For the Com- modore 64/128, you could use the following statement: 10 IF (PEEK(56321) AND 2T0) = THEN PRINT "YES" On the VIC-20, you'd use this instead: 10 IF (PEEK(37137) AND 2T0) = THEN PRINT "YES" Since the zero bit in the memory location (the reg- ister) corresponds with pin 1 (the I/O line), the word YES is printed if this bit is set low. When outputting data, your program must alter the contents of the data port and set the port for output. Suppose you want to set pin 1 of port 2 to output a logic high signal. To do this, your pro- gram must set bit in the data direction register to a 1 for output: 81 CHAPTER 8 For Commodore 64/128: 10 POKE 56321,PEEK(56321)OR(2T0) For Commodore VIC-20: 10 POKE 37137,PEEK(37137)OR(2t0) Each I/O pin of the control port has a cor- responding bit in the data direction register. When a control port pin is to be used for input, its bit in this register must be set low. Setting a data direc- tion register bit high, on the other hand, makes its corresponding control port pin an ouput line. The data lines are normally set for input — that's why you could ignore this register when you were first exploring the control port. However, when you want the computer to out- put signals, this register must first be set. The data direction registers are located at memory locations 56322 ($DC02 in hexadecimal) for joystick port 2 and 56323 ($DC03) for joystick port 1 on the Commodore 64 and 128, and location 37139 ($9113) for the VIC-20. The Atari Computers The Atari computers are a little different when it comes to sending and receiving data. A data regis- ter and data direction register are still used, but unlike the Commodore computers, the Atari's reg- isters are both at the same memory location. Though you previously used the BASIC STICK command to check input to the control port, you can also use one of the computer's registers di- rectly to obtain the same information. Bits 0-3 of memory location 54016 ($D300) correspond to pins 1-4 of control port 1, respectively, while bits 4-7 correspond to pins 1-4 of control port 2. By PEEKing this memory location, you can see what data has been input through the control ports. This same register is used to send information out of the computer using the control ports' lines. This 82 An Electronic Switch is done by POKEing values into the register to set the bits corresponding to the control ports' pins either high or low. Memory location 54016 is used as a data register and contains the information be- ing either sent or received. Memory location 54016 acts as a data register, accepting incoming data, as long as bit 2 of mem- ory location 54018 ($D302) is set to 0. If bit 2 of memory location 54018 is set to 1, location 54016 acts as a data direction register. Outgoing data can now be sent. The control ports' pins are set as either input or output lines, depending on whether their corresponding bits of the data direc- tion register are 0's or l's. You can set memory lo- cation 54016 to be the data direction register by POKE 54018,48 and return it to acting as a data register with POKE 54018,52 Note: With Atari BASIC, you cannot mask or force bits using ANDs and ORs in POKE statements as with Commodore computers. To set an individual bit in a memory location high, you can POKE the value directly, such as POKE location, Tbit where location is the memory address you wish to change and bit is the bit within that address that you wish to set. For example, to set bit 2 of loca- tion 54016, you would use POKE 54016,4 Without AND and OR, there's no easy way to change a single bit without affecting the current settings of the other bits in the location. For ex- ample, if location 54016 already has bits 6 and 7 set (corresponding to a value of 192 in the loca- tion) and you wish to set bit 3 without affecting the others, then the value you must POKE into 54016 is 200, 192 + (2 A 3). 83 Using a Computer's Output Signals How can an on/off signal from the computer con- trol events in the outside world? An electronic cir- cuit is required to take the digital signals that the computer outputs and perform some useful task. One example of this type of circuit is the elec- tronic switch you'll make. It allows your computer to switch things on and off under the control of a computer program. Building the Electronic Switch You'll need these parts to construct your electronic switch: Part Quantity Part Number 1 9-pin D-subminiature female 276-1538 1 2N2222 NPN transistor 276-1617 1 2.2K ohm resistor 271-8027 1 IN914 diode 276-1620 1 5 -volt SPDT DIP relay 275-243 1 LED 276-041 1 Solderless breadboard 276-175 1 7400 IC (Atari) 276-1801 You'll also need some solid copper wire for con- nections to the 9-pin plug, as well as for jumper connections on the solderless breadboard. Follow these steps to build your electronic switch if you have a Commodore computer (the steps are identical for the Atari, though some ad- ditional steps are listed below). 1. The first step in constructing the electronic switch is to wire the 9-pin plug. Cut three pieces of wire about four inches long and re- move about 1/4 inch of the insulation from each end. An Electronic Switch 2. Solder wires to pins 1, 7, and 8. 3. Connect the three wires as follows: The wire from pin 8, the ground wire, connects to point Yl on the solderless breadboard. The +5- volt wire from pin 7 connects to point XI of the solderless breadboard. The data line from pin 1 connects to location B4 on the board (except for the Atari version — see below). 4. Connect the 2.2K ohm resistor between points A4 and F4 on the solderless breadboard. 5. Mount the 2N2222 transistor so that its base inserts into point H4, its emitter into point H3, and its collector into point H5. Figure 8-1 . Pin Diagrams for Typical 2N2222 NPN Transistors Pin 1. Emitter 2. Base 3. Collector Here are three of the most common 2N2222 NPN transistor con- figurations you'll find. 6. The diode is connected so that its cathode lead inserts into point X5 of the solderless bread- board and its anode lead connects to point B5. (A band around one end of the diode is gener- ally used to identify the cathode lead.) 7. The SPDT relay is inserted so that its normally open and normally closed pins attach to points F9 and E9 respectively. The common pin con- nects to point E14. Continue with step 8 on page 88. 85 CHAPTER 8 u n ; Q X Z Z w ^ „ s 3 tn H O a o d « o I co O c o o CD H D a- 1/5 O Z u z o o O) c > D Q O o E CD .C O co c\i © ZD D ft m An Electronic Switch < -• p § *-nm-» •-f— \A/W v D Z o co u D « u. O S i4 -C CHAPTER 8 8. The following jumper connections are required to complete the electronic switch. Wire From To 1 J3 Y3 2 J5 J10 3 E5 F5 4 X10 A10 Additional Steps for Atari Version Only 9. Insert the 7400 IC into the solderless bread- board so that its pins 1 and 8 go into plug points F16 and E22 respectively. 10. Insert the wire from pin 1 of the 9-pin plug into point J16 of the solderless breadboard. 11. Add the following jumper connections. Wire From To 5 X16 A16 6 J22 Y22 7 H16 G17 8 G18 G19 9 H19 G20 10 G21 B4 Switch Is On The 9-pin plug connects to control port 1 of your computer. The circuit draws its power from the computer's power supply through the wires from pins 7 and 8. The wire from pin 1 provides the circuit with a digital signal. This signal can be set by the program to be either logic high or logic low. Pin 1 of the control port is connected to the base of the transistor through a current-limiting resistor. If the signal from the computer is +5 volts (logic high), current flows from this pin through the base of the transistor. This base cur- rent causes the transistor to act as a closed switch between its emitter and collector leads. When the 88 An Electronic Switch CHAPTER 8 transistor acts as a closed switch, current flows from the + 5 volts of the power supply through the coil of the relay to ground. The relay turns on due to this coil current. The Atari version of the circuit uses two NAND gates as a noninverting buffer. This buffer is required since the signal from the Atari's control port is not sufficient to turn on the transistor. Refer to Chapter 10, "Digi- tal Logic," for more on buffers and gates. When a logic low signal (0 volts) is present at pin 1, no base current flows in the transistor. As a result, the transistor acts as an open switch across its emitter and collector leads. Consequently, the relay assumes its off position since no current flows through its coil. The relay is an electromechanical switch. The device to be controlled is connected to the relay via its common, normally open and normally closed terminals. The circuit which controls the device is attached to the coil terminals of the relay. When the relay is off, a metal lever bridges the gap between its common and normally closed ter- minals. The coil of the relay is part of an electro- magnet. When current flows through this coil (to turn the relay on), the electromagnet pulls the metal lever so that it bridges the gap between the common and normally open terminals instead. Many electric devices can be switched on and off by this circuit. A description of using the cir- cuit to turn on an LED appears below. To use this circuit to control other devices, connect the de- vices between points G9 and D14, the two points marked A in Figure 8-3. Other devices should have their own power supply, such as a battery connected in series with point G9 or D14 and the device itself. (You can see the connection from the breadboard to a 6-volt battery in Figure 8-4.) Cau- tion should be exercised not to exceed the current rating of the SPDT DIP relay. 90 An Electronic Switch Figure 8-5. Through with the Breadboard . . ■ * * * w *■ iyi if * * v •«.«» ... * «' » ■ The electronic switch can be used to control a variety of devices. Using the Electronic Switch — Flashing an LED Here's one application for your electronic switch — a computer-controlled LED. The computer pro- gram, with the aid of the electronic switch, turns on the LED after a specified time delay. For this application, you'll need to connect two jumper wires and the LED. 1. Connect a wire between points X8 and G9 on your solderless breadboard. 2. Also connect a jumper between points Y15 and J15. 3. Plug the cathode of the LED into point D15 and its anode into D14. First of all, insert the 9-pin plug of the electronic switch circuit into control port 1 of your computer. Next, turn on your computer. 91 CHAPTER 8 Enter and run the appropriate version of Program 8-1. The program prompts you to enter the hours, minutes, and seconds of the delay. After you enter the delay, the computer will wait that length of time before turning on the LED — the LED will re- main on for only about five seconds. To turn on the LED, the program sets pin 1 of the control port to logic low. This turns off the re- lay, closing the connection between its common and normally closed terminals. Program 8-1 — Commodore 64/128 KR 10 PRINT "ENTER HOURS"; BK 20 INPUTA SS 30 PRINT "ENTER MINUTES"; DP 40 INPUTB SG 50 PRINT "ENTER SECONDS"; RR 60 INPUTC GP 70 D=(A*216000)+(B*3600)+(C*60) QE 80 REM START TIMER QR 90 TIS="000000" RM 100 IFTI > DTHEN1 30 QH 110 GOTO100 KX 120 REM SET DATA LINES FOR OUTPUT JJ 130 POKE 56323, PEEK(56323)OR(2T0) DH 140 REM SET DATA LINES TO LOGIC LOW T O TURN ON BUZZER CF 150 POKE 56321 , PEEK ( 56321 )ANDNOT( 2l0) FX 160 REM KEEP BUZZER ON FOR FIVE SECON DS AA 170 TI$="000000" DK 180 IF TI>300 THEN210 HB 190 GOTO180 SQ 200 REM SET DATA LINE TO LOGIC HIGH T O TURN OFF BUZZER XJ 210 POKE 56321, PEEK ( 5632 1 ) OR{ 2 ?0 ) FC 220 REM RESET DATA LINE FOR INPUT QQ 230 POKE 56323, PEEK ( 563 2 3 ) ANDNOT ( 2 t ) Program 8-1 — VIC-20 KR 10 PRINT "ENTER HOURS " ; BK 20 INPUTA SS 30 PRINT "ENTER MINUTES"; DP 40 INPUTB 92 An Electronic Switch SG 50 PRINT "ENTER SECONDS"; RR 60 INPUTC GP 70 D=(A*216000)+(B*3600)+(C*60) QE 80 REM START TIMER QR 90 TI$="000000" RM 100 IFTI>DTHEN130 QH 110 GOTO100 KX 120 REM SET DATA LINES FOR OUTPUT BM 130 POKE 37139, PEEK ( 37 1 39 ) OR( 2? 2 ) DH 140 REM SET DATA LINES TO LOGIC LOW T TURN ON BUZZER BD 150 POKE 37137, PEEK ( 371 37 ) ANDNOT ( 2T2 ) FX 160 REM KEEP BUZZER ON FOR FIVE SECON DS AA 170 TI$="000000" DK 180 IF TI>300 THEN210 HB 190 GOTO180 SQ 200 REM SET DATA LINE TO LOGIC HIGH T O TURN OFF BUZZER GM 210 POKE 37137, PEEK( 37137 )OR( 2?2 ) FC 220 REM RESET DATA LINE FOR INPUT RM 230 POKE 37139, PEEK ( 37 139 ) ANDNOT ( 2T 2 ) Program 8-1 — Atari IS 100 REM TIME BUZZER KO120 PRINT "ENTER HOURS"; 6F 130 INPUT A EE 140 PRINT "ENTER MINUTES"; GI 150 INPUT B DA 160 PRINT "ENTER SECONDS"; GL 170 INPUT C PP 1S0 D= (A*2 16000) + (B*3600) + (C*60) OE190 POKE 18,0:POKE 19,0:POKE 20,0 OJ 200 IF ( (PEEK ( IB) #255*255) + (PEEK < 19) *255) + (PEEK (20) 5 ) >D THEN 2 20 FO210 SOTO 200 NF215 REM SET DATA LINES FOR OUTPUT FN 220 POKE 54018,48 JA 225 POKE 54016,255 FJ 230 POKE 54018,52 UK 235 REM SET DATA LINES LOGIC LOW TO TURN ON BUZZER CB 240 POKE 54016,0 OF 245 POKE 18,0:POKE 19,0:POKE 20,0 EC 250 IF < (PEEK ( 18) *255*255) + (PEEK ( 19) #255)+ (PEEK (20) ) ) >300 THEN 270 93 CHAPTER 8 SI 260 GOTO 250 ML 265 REM SET DATA LINES HISH TO TU RN OFF BUZZER JA270 POKE 54016,255 AN 280 REM RESET DATA LINES FOR INPU T 6E290 POKE 54018,48 BO 300 POKE 54016,0 FI 310 POKE 54018, 52 Other Applications The LED flasher is just one application of the elec- tronic switch. You can use your electronic switch to turn on any electric device, anything from an alarm to a light, so long as the ratings of the relay and solderless breadboard are not exceeded. Sim- ply wire the device and its power supply to the relay as if you were using an ordinary switch. Warning: If you're planning on using the switch to turn on lights, a coffee pot, or any appliance con- nected to house line voltage, remember that the relay must be rated to handle the current needed by the appliance. Potentially lethal voltages will be present at the relay. The relay should be housed in a container to prevent accidental contact, and good electrical practices should be employed. For additional safety, a buffer circuit should be em- ployed to further isolate your computer (and your- self) from high voltages. 94 A Burglar Alarm A burglar alarm is supposed to detect an intruder. To do that, though, the alarm must be as sophisti- cated as possible to detect and act upon a variety of situations. A computer, equipped with the proper sensors and actuators, can do just this and become an effective burglar alarm. Intruders may reveal their presence to a computer-controlled burglar alarm in a number of ways. First of all, the intruder must somehow enter the building — a door or window is the most logical means of entry. If the computer's sensors are set to detect use of these entrances, an alarm can be triggered when someone passes through them. Sensors could also be set to detect anyone in areas considered off-limits. For instance, if a sen- sor detects someone in the living room when all rightful occupants are sleeping upstairs, the bur- glar alarm can safely assume that an unauthorized person is in the protected area. Another possibility is to have the alarm sensors detect movement of particular objects. Most car alarms work on this principle. The sensors can be set to tell whether your stereo, television, or any- thing else has been moved. If an intruder tries to steal something, the burglar alarm can alert you, or even alert the police. Using What You Know The previous projects in this book laid the groundwork for a burglar alarm. In particular, the joystick project in Chapter 3 and digital light sen- sor project in Chapter 7 will be used as the sen- 97 CHAPTER 9 sors. The electronic switch project, found in Chapter 8, is the actuator required by the alarm. If you didn't put them together earlier, turn back now and try them. Be sure you have a basic un- derstanding of these circuits before proceeding. You'll need to refer to these chapters as you con- struct this burglar alarm. As you saw in Chapters 2 and 3, a computer joystick is actually a set of switches. Many types of burglar alarm sensors are switches as well. These sensors can be connected to your computer in the same way as a joystick — through the I/O lines of the control port. One type of switch sensor is a thin, adhesive, metallic tape that can be stuck on windows and other glass. This tape normally acts as a closed switch, allowing current to flow through a circuit. If the glass is broken, the fragile tape breaks, too, and the circuit is interrupted. Another type of switch sensor is a magnetic switch. This sensor is generally used to detect doors and windows being opened or closed, but it could also be installed on desk drawers. A typical application is a magnet mounted on a door, with the magnetic switch mounted on the door frame. When the door closes, the magnetic switch either closes or opens, depending on the type of switch. When the door opens, the magnetic switch changes. Other types of sensor switches include vibration detectors, ultrasonic sensors, and even infrared sensors. Most of these "switch" alarm sensors can be purchased at electronic stores such as Radio Shack. Your alarm will use the digital light sensor project built earlier to detect entry into an off-limits area. The light source and sensor should be set up so that any light in the controlled area will trigger the sensor. 98 A Burglar Aiarm The computer will use the electronic switch to turn on the alarm itself. The alarm can be a buzzer or a louder alarm (providing it doesn't exceed the ratings of the relay or solderless breadboard). With the proper programming, your computer could even use a modem to call the police, and then play a tape recording announcing your address and reporting a break-in. Setting Up the Alarm To set up your computer as a burglar alarm, plug the electronic switch into control port 1. Before placing the digital light sensor's 9-pin plug into control port 2, solder wires for switch sensors to its pins 2, 3, 4, and 6. Figure 9-1 . Atari and Commodore 64/1 28 Burglar Alarm Switches r Normally closed switches represent switch sensors Pin 2 To 9-pin Plug J of \ light Pin 3 Pin 4 Pin 6 To Pin 8 "Q l_£T (or any ground connection) Notes Digital light sensor plug inserts into control port 2. Only additions to this circuit are sensors illustrated above. Electronic switch circuit plugs into control port 1 unaltered. The alarm sensors are wired to the digital light project's 9-pin plug. 99 CHAPTER 9 If you have a VIC-20, you need a new connec- tor since both the electronic switch, the digital light sensor, and the other switch sensors must be plugged into the single control port. To do this, you need to make a new connector: 1. Solder wires to pins 1, 2, 3, 4, and 6 of a 9-pin plug. Solder two wires each to pins 7 and 8. 2. Remove the old connectors from the electronic switch and light sensor cicuits. 3. The wire from pin 1 of the new connector in- serts into point A4 of the electronic switch cir- cuit. It provides the digital signal required to turn the electronic switch on or off. 4. The wire from pin 2 connects to point 14 of the light sensor circuit to receive its digital output signal. 5. The wires from pins 7 and 8 provide the power to the two circuits. One set of two wires from pins 7 and 8 connects to points Yl and XI re- spectively of the light sensor circuit board. The other set of two wires from pins 7 and 8 con- nects to points XI and Yl respectively on the electronic switch circuit. The remaining wires from the control port are used for switch sensors. Whichever type (or types) of switch sensors you choose for your burglar alarm, they must be nor- mally closed. They're set up so that they ordinarily form a closed loop between the ground pin of the control port and one of the I/O pins. The Commo- dore 64, 128, and Atari computers can each have four switch sensors connected to them in addition to the light sensor. The VIC-20 can have three switch sensors in addition to the light sensor. For any of the machines, there's no need to wire one end of the switch sensors directly to pin 8 of the control port — any connection to ground, such as the x row of the light sensor circuit, will do. 100 A Burglar Aiarm Figure 9-2. VIC-20 Burglar Alarm Switches To point A4 of electronic switch solderless breadboard Pin 1 To point 14 of digital light sensor solderless breadboard Pin 2 . Normally closed switches represent jf switch sensors Pin 3 - Pin 4 Pin 6 Pin 8 o o o < 1 fl — (or any ground) Notes One wire from pin 7 inserts to point Yl of electronic switch solderless breadboard. One wire from pin 8 inserts to point XI of electronic switch solderless breadboard. Second wire from pin 7 inserts to point XI of digital light sensor. Second wire from pin 8 plugs into point Yl of digital light sensor. You must have special connector to build the burglar alarm for the VIC-20 since the computer has only one control port. CHAPTER 9 Since, in normal conditions, the switch sensors form a closed loop between ground and their par- ticular I/O lines, these lines are at a logic low level. Similarly, the digital light sensor circuit out- puts a logic high signal as long as no light is de- tected. The computer program of the burglar alarm can tell if things are as they should be just by checking to make sure that the bits in the data register corresponding to the sensors are off. If one of the sensor bits of the data register has changed, this means one of the sensors has been activated — its corresponding I/O line no longer forced to ground. The burglar alarm program must detect if this happens and send a signal to the electronic switch to turn on the alarm. You may want to experiment with infrared emitters and detectors, such as those used in the digital timer project of Chapter 7. In a darkened hallway, you might be able to use the digital timer as a switch for an intruder alert. Other infrared detectors and emitters could be purchased. Program 9-1 is a simple demonstration program il- lustrating the use of your computer-controlled burglar alarm. Once you have the basic circuitry working, you can modify the program and circuit to add additional sensors as necessary. If you need more sensors than this simple alarm allows, refer to the multiplexer project of Chapter 12. Program 9-1 —Commodore 64/1 28 MH 120 PRINT " { CLR } ADJUST THE INFRARED BE AM AND THE" FA 130 PRINT "POTENTIOMETER UNTIL THE MES SAGE JUST" GQ 140 PRINT "CHANGES FROM OFF TO ON" KX 150 PRINT: PRINT "PRESS X TO CONTINUE" SF 160 AS=CHR$(145) PM 165 A=PEEK( 56320) BJ 170 IF (A AND 2?0) THEN PRINT "OFF" XM 175 IF (A AND 2?0)=0 THEN PRINT "ON " 102 A Burglar Alarm KE 180 GET B$ FK 190 IF B$="X"THEN220 PH 200 PRINTA$A$ AD 210 GOT0165 EK 220 PRINT "TRIGGER A SENSOR TO START A LARM " HQ 225 REM CHECK SENSOR STATUS MX 230 B=PEEK(56320) QH 240 IF B=A THEN 230 JQ 250 PRINT "WARNING-ALARM TRIGGERED" AG 260 FOR 1=0 TO 4 AA 270 IF (B AND 2TD THEN PRINT "SENSOR ";I+1;" DETECTS VIOLATION" EH 280 NEXT I MM 340 TI$=" 000000" QM 370 REM TURN ON ALARM SQ 375 REM SET DATA DIRECTION REGISTER F OR OUTPUT XJ 380 POKE 56323,PEEK(56323)OR(2T0) AM 385 REM SET DATA LINE LOGIC LOW TO TU RN ON ALARM HF 390 POKE 56321, PEEK ( 56321 ) ANDNOT ( 2T0 ) QC 395 REM ALARM ON FOR 2.5 SECONDS KE 400 IF TI>3600/24 THEN 420 GP 410 GOTO 400 BP 420 REM SET DATA LINE LOGIC HIGH TO T URN OFF ALARM AK 430 POKE 56321, PEEK ( 5632 1 ) OR ( 2 T0 ) JR 440 REM RESET DATA DIRECTION REGISTER FOR INPUT PM 450 POKE56323,PEEK(56323)ANDNOT(2T0) Program 9-1 — VIC-20 GE 10 PRINT "TURN ON FLASHLIGHT AND ADJUS T THE" GG 20 PRINT "POTENTIOMETER TILL THE MESSA GE JUST" SR 30 PRINT "CHANGES FROM OFF TO ON" KQ 40 PRINT: PRINT "PRESS X TO CONTINUE" GM 50 A$=CHR$(145) PB 60 A=PEEK( 37137 ) HS 70 IF (A AND 2T3) THEN PRINT "OFF" FH 80 IF (A AND 2?3)=0 THEN PRINT "ON " XA 90 GET B$ MH 100 IF B$="X"THEN130 QB 110 PRINTA$A$ SQ 120 GOTO60 103 CHAPTER 9 DX 130 PRINT "TRIGGER A SENSOR TO START A LARM " QG 140 Z? = " DETECTS VIOLATION" MG 150 REM CHECK SENSOR STATUS ES 160 B=PEEK( 37137) FS 170 POKE37154,0:IF(PEEK(37152)AND(2T7 ) ) THEN PRINT "SENSOR 3 " ; Z$ :GOTO230 EF 180 IF B=A THEN160 RP 190 PRINT "WARNING- ALARM TRIGGERED" GG 200 IF (B AND 2?3) THEN PRINT "SENSOR 1";Z$ MM 210 IF (B AND 2?4) THEN PRINT "SENSOR 2";Z$ DX 220 IF (B AND 2T5) THEN PRINT "SENSOR 4";Z$ HB 230 POKE 37154,255 XE 240 TI$="000000" PC 250 REM TURN ON ALARM GH 260 REM SET DATA DIRECTION REGISTER F OR OUTPUT HB 270 POKE 37139,PEEK(37139)OR(2T2) PR 280 REM SET DATA LINE LOGIC LOW TO TU RN ON ALARM PM 290 POKE 37137,PEEK(37137)ANDNOT(2T2) RM 300 REM ALARM ON FOR 2.5 SECONDS BC 310 IF TI>3600/24 THEN330 SG 320 GOTO310 HB 330 REM SET DATA LINE LOGIC HIGH TO T URN OFF ALARM CB 340 POKE 37137,PEEK(37137)OR(2T2) AC 350 REM RESET DATA DIRECTION REGISTER FOR INPUT EF 360 POKE37139,PEEK( 37 1 39 ) ANDNOT ( 2T2) Program 9-1 — Atari PL 110 REM ALARM PROGRAM KP120 PRINT "TURN ON FLASHLIGHT AND ADJUST THE" LF 130 PRINT "POTENTIOMETER TILL THE MESSAGE JUST " K0 140 PRINT "CHANGES FROM OFF TO ON It FE 150 PRINT " PRESS X TO CONTINUE" 6H 155 FOR J = l TO 2500:NEXT J BP 160 IF STICK(1)=1 THEN PRINT "OFF II DB 170 IF STICK<1>=0 THEN PRINT "ON 104 A Burglar Alarm (IB 180 KD 190 6C 200 ML 2 1 CH 220 DD 230 NI 240 611 250 LS 260 OC 270 OF 280 OJ 290 PA 292 ON 294 CF 300 NK 305 NO 310 NC 320 FP 330 10 340 Ffl 350 OG 360 CF 370 AM 380 HA 390 OF 400 IH 410 AJ 420 6A 430 CD 440 FN 450 REM CHECK IF X KEY PRESSED IF PEEK(764)=22 THEN 210 GOTO 160 REM CLEAR OUT LAST KEYSTROKE POKE 764,255 PRINT "TRIGGER A SENSOR TO ST ART ALARM " A=STICK(1) :B=STRIG(1) IF (A = AND B=0) THEN 240 PRINT "WARNING - ALARM TRIGGE RED" IF A=l THEN PRINT "SENSOR 1" IF A=2 THEN PRINT "SENSOR 2" IF A=4 THEN PRINT "SENSOR 3" IF A=8 THEN PRINT "SENSOR 4" IF B=l THEN PRINT "SENSOR 5" PRINT "DETECTS VIOLATION" REM INITIALIZE CLOCK POKE 18,0:POKE 19,0:POKE 20,0 REM SET DATA LINES FOR OUTPUT POKE 54018,48 POKE 54016,255 POKE 54018,52 REM SET DATA LINES LOW TO TUR N ON ALARM POKE 54016,0 IF ( (PEEK ( 18) #255*255) + (PEEK ( 19) *255> + (PEEK (20) ) ) >3600/24 THEN 400 GOTO 380 REM TURN OFF ALARM BY SETTING DATA LINES LOGIC HIGH POKE 54016,255 REM RESET DATA LINES FOR INPU T POKE 54018,48 POKE 54016,0 POKE 54018,52 Before mounting sensors, you should first check your burglar alarm. The switch sensors can be simulated by connecting their I/O pin wires to the ground of either of the circuits. When you run the appropriate version of Program 9-1, you're in- structed to carry out the necessary adjustment to the digital light sensor. Once you do this, your burglar alarm is operational. 105 CHAPTER 9 To trigger the alarm, shine a light on the light sensor or disconnect a switch sensor wire from ground. The program prints on the screen which sensor was triggered and turns on the alarm after a delay of several seconds (so that an authorized person could disable the alarm). The alarm stays on for a couple of seconds before shutting off. You'll probably want to increase the delay of tim- ers when you install the system. (Of course, a power failure will disable the alarm. The program will have been removed from your computer's memory.) Other Applications Not all the applications for this project are as seri- ous as a burglar alarm. You could mount a mag- netic switch on the refigerator door to make sure someone isn't cheating on a diet. If you have a small store, you could use this project to sound a buzzer when a customer enters. With some thought, you can modify the program and circuit for almost any application. 106 CHAPTER 10 Digital Logic Until now, whenever a digital output signal was required, you took it directly from one of the com- puter's control port I/O lines. Similarly, all the sensors sent their digital output signals directly to a control port pin. Every digital signal, whether input or output to the computer, needed its own I/O line. Advanced projects cannot be interfaced to your computer like this — there simply are not enough I/O lines available. The control port gives you ac- cess to five I/O lines. But what if you need to control 12 electronic switches or monitor 15 sen- sors? Or even do both at the same time? The solu- tion to this predicament is to use digital circuitry to manipulate the signals the computer sends and receives. Digital circuitry is the same type of circuitry your computer uses. The uses of these types of circuits include performing calculations, storing information, and controlling the flow of digital signals. The behavior of digital circuits is de- scribed by what is known as Boolean algebra. Even the most complex digital circuits, like the microprocessor of your computer, are created from basic building blocks. These building blocks are called gates. A gate has one or more input lines and only a single output line. The input lines are used to input binary data in the form of on/off signals. A gate combines these signals to produce an output. The output signal is either logic high (on) or logic low (off). The relationship between the input signals and the output signal of a gate is given by its truth table. 109 CHAPTER 10 In the following descriptions, you'll see H and L listed. They represent: H = Logic high On 1 signal L = Logic low Off signal The main types of gates, along with their truth tables, follow. Noninverting Buffer This is the simplest of all gates. The signal that appears at its input is the same as the signal on its output. Figure 10-1 . Symbol for a Noninverting Buffer NOT Gate NOT gates are often called inverters. A NOT gate's output signal is the opposite of its input sig- nal. Note that the symbol of the NOT gate is the same as that of the buffer, except for the small cir- cle near its output. Small circles at input or output lines of a gate's schematic symbol denote the fact that the signal is inverted. Figure 1 0-2. Symbol for a NOT Gate Output Input L H Output L H Output 110 Digital Logic Input Output L H H L AND Gate This gate has two or more inputs. Its output goes logic high only if all the inputs are logic high. Figure 10-3. Symbol for an AND Gate A B Input Output A B L L L L H L H L L H H H Output NAND Gate This gate has two or more inputs and only one output. Its output goes logic low only if all the in- puts are logic high. For all other input conditions, the output is logic high. Note that the output of the NAND gate is the opposite of that of the AND gate for indentical input signals. Figure 1 0-4. Symbol for a NAND Gate Output Input Output A B L L H L H H H L H H H L 111 CHAPTER 10 OR Gate The output of an OR gate goes high if any of its two or more input lines are set high. Figure 1 0-5. Symbol for an OR Gate Output Input Output A B L L L L H H H L H H H H NOR Gate A NOR gate is identical to an OR gate with its output inverted. The output of a NOR gate is logic high only if all the inputs to the gate are logic low. Figure 1 0-6. Symbol for a NOR Gate Output Input Output A B L L H L H L H L L H H L Exclusive OR Gate The output of this gate goes high if one input (but not more) goes logic high. r> 112 Digital Logic Figure 10-7. Symbol for an Exclusive OR Gate Output Input Output A B L L L L H H H L H H H L Exclusive NOR Gate The exclusive NOR gate has a logic low output when one (but not more) of the input lines is logic high. Its output is the same as that of an exclusive OR gate with its output inverted. Figure 10-8. Symbol for an Exclusive NOR Gate Output Input Output A B L L H L H L H L L H H H Combining Gates Logic gates can be combined in various ways. Two input gates can be combined to make three (or more) input gates. Figure 10-9 shows how three two-input AND gates can be used to produce a four-input AND gate. 113 CHAPTER 10 Figure 1 0-9. Three Two-Input AND Gates Form a Four-Input AND Gate Output Its function can be verified by using the following truth table: Input Intermediate Output A B C D E F L L L L L L L L L L H L L L L L H L L L L L L H H L H L L H L L L L L L H L H L L L L H H L L L L L H H H L H L H L L L L L L H L L H L L L H L H L L L L H L H H L H L H H L L H L L H H L H H L L H H H L H L L H H H H H H H Logic gates can even be combined to form other logic gates. A NAND gate or a NOR gate acts as an inverter (NOT) if both the input lines are joined together. Figure 1 0-1 0. NAND Gate As a NOT Gate A Input A 6 C D Output 114 Digital Logic Figure 10-11. NOR Gate As a NOT Gate A Input B Output Three two-input NAND gates can be hooked up to form an OR gate. Figure 10-12. Three Two-Input NAND Gates As OR Gate Output NAND and NOR gates are extremely useful since they can be wired to operate as any type of gate. These gates can be combined in an unlimited number of ways. Once you understand the basic functions of the gates, putting together a digital circuit to meet specific requirements is fairly easy. Decoders and Encoders Also referred to as demultiplexers and multiplexers, decoders and encoders can be used by your com- puter to send or receive digital signals on many different lines using fewer pins of the control port. These circuits can help you solve the problem of controlling and sensing several different devices using a limited number of I/O lines. Like all digi- tal circuits, decoders and encoders are constructed from the basic gates discussed earlier. The decoder circuit in Figure 10-13 lets your computer output digital signals on four lines using 115 CHAPTER 10 only two lines of the control port. The two control port lines can output the binary numbers 00 (0 decimal) to 1 1 (3 decimal) in the form of high and low signals. One of the four output lines of the demultiplexer outputs a logic high signal depend- ing on the input combination received from the control port. The other three outputs remain logic low. While the decoder allows you to turn on four electronic switches (or whatever) using two con- trol port lines, there is a catch — you can switch on only one device at a time. In many applications this tradeoff between control port lines and flex- ibility will work to your advantage. Try tracing the logic of the demultiplexer in Fig- ure 10-13. You'll see that the inputs of the AND gates are wired to the input lines and inverted in- put lines from the control port in a way that al- ways produces the expected output. The number of outputs you can design in a de- coder depends upon the number of control port lines you have available. If you have X control lines, you can make a demultiplexer with 2~X out- puts. Of course, you would also need X inverters (NOT gates) and TX AND gates to build it. Multiplexers, or encoders, perform the opposite function of decoders. They let you input digital signals from several lines to a single control port pin. As you can see from Figure 10-14, the cir- cuitry for an encoder is similar to a decoder, with some additions. Each output of the demultiplexer section (the part on the left in Figure 10-14) is con- nected to an AND gate. The other lead of the AND gate is connected to one of the four lines carrying information from the sensors to the computer. 116 Figure 10-13. Decoder (Demultiplexer) Circuit (from computer's control port) Input A Input B Output signals (to control port) Output Z Output Y Output X Output W Truth Table Input Output A B Z Y X W L L H L L L L H L H L L H L H H L L H L L L L H CHAPTER 10 The demultiplexer part of this circuit is used to select which of the four sensor lines is effectively connected to the control port pin. The line con- nected to the AND gate whose other input is logic high (from the demultiplexer part) has its signal passed to the OR gate and through to the control port. The signals from the lines connected to AND gates whose other inputs (from the demultiplexer section) are low are in essence blocked from the inputs of the OR gate. The only data line signal therefore "seen" by the control port is the one selected by the demulti- plexer circuit. A multiplexer with X control port pins available can be designed to allow 2*(X — 1) digital input lines to be connected to the com- puter. The value X— 1 comes from the fact that one pin must be used to input the actual data, while the remaining pins are used to select the data line. These encoder and decoder circuits may seem too large to set up on a solderless breadboard. Using individual chips, they would be. Fortunately entire multiplexers and demultiplexers are avail- able on integrated circuit "chips." All you need to do is properly connect their pins to the control port. In fact, this procedure is described in Chap- ter 12, "More Ideas." Experimenting with Digital Logic The best way to learn and understand how digital circuitry works is to do some hands-on experi- menting. All the different types of gates are avail- able on integrated circuit (IC) chips. All you need are a few chips, a solderless breadboard, a power supply, some wire, and a logic probe to get started. 118 Digital Logic 3 3 o o h n n "3 3 "3 "3 Dh Ph Dh Ph c c c c nj nj nj nj -*— ' -4— ' -4— » -4— » '5b'5b'5b'3b QQQQ £ "3 PQ 3 60 3 o © X ® Q. Et=tJ o ZD .£P§ § pa CHAPTER 10 The integrated circuits you should use are TTL or LS types. These chips usually contain one or more gates. The 7400, for instance, is four two- input NAND gates in one IC package. It's a TTL (Transistor-Transistor Logic) IC. The 74LS00 is identical to the 7400 IC, except it uses less power (LS stands for Low-power Schotkey). In fact, most TTL ICs have LS versions. TTL IC names start with the digits 74. Low- power Schotkey ICs follow this identifier with the letters LS. The remaining part of the names are the same for TTL and LS ICs which are functionally identical. The pin layouts for the integrated circuits used in this book, as well as some additional basic ICs, appear in Appendix B. Simply connect the ground and Vcc pins of the chip to a power supply. Be careful wiring the ICs to the power. If you reverse the connections, you could destroy the IC. If you're using only a couple of chips, you can tap your computer's control port for power. Pin 7 can supply +5 volts with up to 50 mA (milliam- peres) of current. Pin 8 is attached to the ground terminals of the computer's power supply. If you're using several ICs, you'll need an exter- nal 5 -volt power supply. When you use a separate external power supply for a digital circuit and in- terface it with your computer, remember to pro- vide a common ground line by connecting the external power supply ground terminal to pin 8 of the control port. 120 a CHAPTER 1 1 " A Better Logic Probe A Better Logic Probe To experiment with digital logic circuits, you'll need a logic probe better than the simple one you built earlier. The logic probe illustrated here is ca- pable of detecting both logic high and logic low states in a circuit. (If you're really serious about experimenting with digital circuits, you should definitely consider buying a commercial logic probe.) To put together this more sophisticated logic probe, you'll need these components: Part Quantity Part Number 2 IK ohm resistors 271-8023 1 Green LED 276-022 1 Red LED 276-041 3 Alligator clips 270-378 1 74LS367 IC None 1 Solderless breadboard 276-175 You'll also need some solid copper wire for the jumpers and some stranded copper wire for probe leads. Here's how to put together the "better" logic probe: 1. Cut three pieces of stranded copper wire about 8 inches long and remove about 1 /4 inch of in- sulation from each end. Attach an alligator clip to one end of each of these wires. 2. Connect the other end of one wire to point Yl of the solderless breadboard. This lead is the ground wire. 123 CHAPTER 1 1 <N (S o 3. Insert one end of another wire, the +5 -volt lead, to point XI of the breadboard. 4. The third wire is the probe lead and is inserted into point 16 of the board. 5. Insert the 74LS367 IC into the breadboard so that its pin 1 goes into point F6, and its pin 9 goes into point E13. 6. Connect three jumper wires as follows: Jumper From To 1 G7 X7 2 J13 Y13 3 X5 A6 7. The IK ohm resistors bridge the following points: Resistor From To 1 H2 H6 2 H7 H14 8. The red LED is mounted on the breadboard so that its cathode plugs into point Y2 and its an- ode into point J2. 9. The cathode of the green LED inserts into point Y14, while its anode plugs into point J14. Figure 11-2. Better Logic Probe • \. • • • • It's easy to see the various parts which make up this better logic probe. 125 CHAPTER 1 1 Probing To use the logic probe, connect the ground wire and +5 -volt wire to the power supply ground and + 5-volt terminals of the circuit you're checking. Touch the probe lead to the point of the circuit you want to check. If the green LED turns on, the point is at a logic low level, but if the red LED lights, the point is at a logic high level. (If neither LED lights, the point is neither at a logic high nor low state.) When the probe is touched to a logic high point of the circuit, current flows through the red LED, causing it to light. The probe is also connected to the enable input pin of the 74LS367 IC. When this pin is high, all the buffer outputs in the chip enter the high impedance state. Since the green LED is connected to the output of a buffer, it remains off. The green LED is effectively disconnected from the circuit since one of its leads is connected to the buffer output, which is acting like a very large resistor (open circuit). When the probe is touched to a logic low point of the circuit, no current flows through the red LED since both its leads are at the same voltage (ground). The low signal, however, enables the 74LS367 IC so that its buffers act normally. Since the buffer (whose output is connected to the green LED) input is attached to + 5 volts, the green LED lights up. This happens because the output of the buffer is logic high, and as a result, a current flows through the green LED causing it to illuminate. Note that due to low current levels, the LEDs may be dim and difficult to see at times. This circuit is very handy for exploring and troubleshooting digital circuits. It's also a worthy candidate for "permanent" mounting on a printed circuit board, perhaps, as you'll probably use it often. 126 CHAPTER 12 More Ideas More Ideas You've built the simple circuits in this book, tried out the programs that accompanied them, and you're ready for more. Now what? Since you've done the work already let's take a look at some more ways to put these circuits to work. Once you start thinking about it, you'll quickly find that there's a very wide range of pos- sible applications for these circuits. And the circuits can even be expanded to perform additional, more complex functions. Here are just a few projects you can create with the circuits you've built. A Two-Beam Digital Timer Circuit To make a two-beam digital timer, you'll need two digital light sensors (see Chapter 7). The two-beam timer begins timing when the first light beam is broken and stops timing when the second light beam is broken. A light sensor is required to monitor each of these light beams. The elapsed time between the two events (breaking the paths of the two light beams) is displayed on the computer's screen. This project is ideal for tim- ing races. It may also be useful in classroom sci- ence experiments where the speed of an object must be measured by timing how long it takes for something to move from point A to point B. You've already built one sensor — the second sensor can be put on the same solderless bread- board as your original circuit. Both light sensors operate in the same way, and the digital sensors even share one major circuit component, the 3900 op amp IC. The 3900 IC has four operational am- plifiers (op amps) built in. Each digital light sensor 129 CHAPTER 12 requires the use of one operational amplifier. The second sensor just uses one of the three unused op amps. In fact, you could build four digital light sensors using a single 3900 IC. Figure 12-2 is the schematic diagram of the two- beam digital timer circuit. For a more reliable switch, infrared sources are recommended. Assuming you have the first digital light sensor at hand (see Chapter 7), here's a list of additional parts you'll need to build this circuit. Part Quantity Part Number 1 500K potentiometer 271-210 (Commodore) 1 1M potentiometer 271-211 (Atari) 1 100K ohm resistor 271-8045 1 10K ohm resistor 271-8034 1 IK ohm resistor 271-8023 1 TIL 414 infrared photo- 276-130 transistor Here's how to construct your two-beam digital timer. 1. Take the solderless breadboard you used to cre- ate the digital light sensor in Chapter 7. Make sure all the components are still on the board and in their proper places. 2. Solder a 4-inch length of copper wire to pin 2 of the 9-pin plug. This wire will provide the computer with the digital signal from the sec- ond sensor. 3. Insert the other end of this wire into point 16 of the solderless breadboard. 4. Solder two wires to the middle and one of the outside leads of the 500K potentiometer. 130 More Ideas 5. The other end of the middle wire goes to point A2 of the breadboard. 6. The wire from the outside lead goes to location X2 of the board. 7. Solder wires to the emitter and collector of the TIL 414 infrared phototransistor. The wires should be long enough so that the phototransis- tor can be mounted properly. Insert the emitter and collector leads into points J2 and Y2 respectively. 8. Bridge the three additional resistors between the following sets of points: Resistor From To Rl (10K ohm) G2 G9 R3 (100K ohm) H9 H10 R4 (IK ohm) 16 110 9. Make the following jumper wire connections (in addition to the jumpers which already exist on the digital light sensor solderless breadboard which you built in Chapter 7) to complete the hardware for the two-light-beam timer: Jumper From To 1 G14 X19 2 F2 E2 Figure 1 2-1 . Two-Beam Timer, the Final Look This mass of wires and electronic components is actually a two- beam timer. 131 CHAPTER 12 More Ideas CHAPTER 12 Using the Two-Beam Timer Plug the 9-pin connector into control port 2 for the Commodore 64/128, or into control port 1 for the Atari computers. To use the timer, set the sen- sors so that the light detect is interrupted when the object being timed passes them. Each sensor must be calibrated using its own potentiometer. Program 12-1 monitors the two digital inputs to the computer from the sensors. When the first sensor is triggered by the passing object, it starts timing. When the object blocks the light to the second sensor, the program stops timing and dis- plays the results. Program 1 2-1 —Commodore 64/128 JF 10 FOR I=0TO1 KF 20 PRINT "TURN ON FLASHLIGHT AND ADJUS T THE " XP 30 PRINT "POTENTIOMETER ";I+1;" TILL T HE MESSAGE JUST" DR 40 PRINT "CHANGES FROM OFF TO ON" CR 50 PRINT: PRINT "PRESS X TO CONTINUE" PM 60 A$=CHR$(145) HM 70 A=PEEK( 56320) DX 80 IF (A AND 2TD THEN PRINT "OFF" BE 90 IF (A AND 2tl)=0 THEN PRINT "ON " JS 100 GET B$ HE 110 IF B$="X"THEN140 JA 120 PRINTA$AS CR 130 GOTO70 AS 140 NEXT I BB 150 PRINT "BREAK BEAM 1 TO START TIMER II GM 160 REM CHECK DATA REGISTER TILL FIRS T SENSOR TRIGGERED MD 170 IF (PEEK(56320)AND(2T0) )=0 THEN17 BH 180 REM START TIMER JD 190 TI$="000000" AG 200 REM CHECK DATA REGISTER TILL SECO ND SENSOR TRIGGERED EM 210 IF (PEEK(56320) AND(2U))=0 THEN2 10 KS 220 PRINT "TIME IS "; TI / 60 ;" SECONDS " 134 More Ideas Program 1 2-1 — VIC-20 SH 10 FOR I=2T03 KF 20 PRINT "TURN ON FLASHLIGHT AND ADJUS T THE" XP 30 PRINT "POTENTIOMETER ";I+1;" TILL T HE MESSAGE JUST" DR 40 PRINT "CHANGES FROM OFF TO ON" CR 50 PRINT: PRINT "PRESS X TO CONTINUE" PM 60 A$=CHR$(145) GB 70 A=PEEK( 37137 ) DX 80 IF (A AND 21 I) THEN PRINT "OFF" BE 90 IF (A AND 2?I)=0 THEN PRINT "ON " JS 100 GET B$ HE 110 IF B$="X"THEN140 JA 120 PRINTA$A$ CR 130 GOTO70 AS 140 NEXT I BB 150 PRINT "BREAK BEAM 1 TO START TIMER II GM 160 REM CHECK DATA REGISTER TILL FIRS T SENSOR TRIGGERED BM 170 IF (PEEK(37137)AND(2T2) ) =0 THEN17 BH 180 REM START TIMER JD 190 TI$="000000" AG 200 REM CHECK DATA REGISTER TILL SECO ND SENSOR TRIGGERED QC 210 IF (PEEK(37137) AND(2?3))=0 THEN2 10 KS 220 PRINT "TIME IS "; Tl/60 ; "SECONDS " Program 12-1 — Atari FL110 REM TWO LIGHT SENSOR TIMER PR OGRAM FJ112 REM CALIBRATE BOTH SENSORS SI 115 FOR 1=0 TO 1 KP 120 PRINT "TURN ON FLASHLIGHT AND ADJUST THE" BE 130 PRINT "POTENTIOMETER ";I + 1;" TILL THE MESSAGE JUST " KQ 140 PRINT "CHANGES FROM OFF TO ON II BL 150 PRINT : PRINT " PRESS X TO CONT INUE" 6B 155 FOR J=l TO 1000.-NEXT J BE 160 A = STICK (0) KK 162 IF 1 = 1 THEN 174 135 CHAPTER 12 PRINT PRINT PRINT PRINT X KEY = 22 THEN 220 "OFF "OFF "ON "ON "OFF 1 "OFF ' "ON "ON PRESSED OJ 164 IF A= 1 5 THEN PRINT OJ 166 IF A=13 THEN PRINT KO 168 IF A=14 THEN PRINT KF170 IF A=12 THEN PRINT 6N 172 GOTO 190 OK 174 IF A=15 THEN OL 176 IF A=14 THEN KO 178 IF A=13 THEN KG 180 IF A=12 THEN MC 190 REM CHECK IF JN 200 IF PEEK<764>= GD210 SOTO 160 NE 220 REM CLEAR LAST CN 230 POKE 764,255 BO 240 NEXT I NF 250 PRINT "BREAK BEAM TIMER" AO 260 REM CHECK FIRST SENSOR RIG6ERED HN 270 IF STICK(0X>13 THEN 270 IN 280 REM START TIMER OF 290 POKE 18,0:POKE 19,0:POKE 20,0 JE 300 REM CHECK SECOND SENSOR UNTIL TRIGBERED II310 IF STICK(0)=14 THEN 320 S6315 GOTO 310 BC 320 PRINT "TIME IS " ; < < PEEK ( 1 8 ) *2 55*255)+(PEEK<19)*255)+<PEEK< 20) ) ) /60; " SECONDS" KEYSTROKE 1 TO START TILL T Light Switch This project combines the analog light sensor from Chapter 5 with the electronic switch you built in Chapter 8. The analog light sensor detects the level of outside light. As night approaches, the computer detects the change in light conditions and turns on a light via the electronic switch. Near dawn, the sensor detects the increase in light, and the computer switches off the light. (Of course, other things, from dark clouds during the day to car headlights at night, may also activate the switch.) 136 More Ideas The analog light sensor, a cadmium sulfide photo- cell, is connected between pins 9 and 5 of the electronic switch's 9-pin plug. Use leads long enough so that the sensor can be aimed easily. The electric light is connected to the relay of the electronic switch across its normally closed and common terminals (remember, the relay turns on as soon as you plug the circuit into the computer's port). Be sure that the ratings of the solderless breadboard or relay are not exceeded by the elec- tric light. The circuit is connected to control port 1 of your computer. Program 12-2— Commodore 64/128 GX 10 PRINT "SET LIGHTING LEVEL TO SWITC H ON" EG 20 PRINT "PRESS X TO CONTINUE" RA 30 A=PEEK( 3687 2 ) HR 40 GET B$ RR 50 IF BS="X" THEN70 XE 60 GOTO30 QG 70 REM HP 80 PRINT "SET LIGHTING LEVEL TO SWITC H OFF " PD 90 PRINT "PRESS X TO CONTINUE" AX 100 B=PEEK(36872) ES 110 GET B$ DF 120 IF B$="X" THEN140 EJ 130 GOTO100 MJ 140 PRINT "PRESS X TO START" FB 150 GET B$ HQ 160 IF B$="X" THEN180 PS 170 GOTO150 PR 180 REM CHECK IF LIGHT LEVEL LOWER TH AN FIRST SETTING FK 190 IF PEEK( 36872) <A THEN190 SP 200 REM SET DATA DIRECTION REGISTER F OR OUTPUT XG 210 POKE 37139, PEEK ( 37139 ) OR( 2T 2 ) CC 220 REM SET OUTPUT LINE LOGIC LOW CG 230 POKE 37137, PEEK( 37137 )ANDNOT ( 2T2 ) HQ 240 REM CHECK IF LIGHTING LEVEL HIGHE R THAN SECOND SETTING FP 250 IF PEEK( 36872) >B THEN250 HQ 260 REM SET OUTPUT LINE LOGIC HIGH 137 CHAPTER 12 RG 270 POKE 37137, PEEK ( 371 37 ) OR( 2T2 ) DG 280 REM RESET DATA DIRECTION REGISTER FOR INPUT FB 290 POKE 37139, PEEK( 37139 )ANDNOT ( 2T2 ) Program 12-2— VIC GX 10 PRINT "SET LIGHTING LEVEL TO SWITC H ON" EG 20 PRINT "PRESS X TO CONTINUE" HD 30 A=PEEK( 54297 ) HR 40 GET B$ RR 50 IF B$="X" THEN70 XE 60 GOTO30 QG 70 REM HP 80 PRINT "SET LIGHTING LEVEL TO SWITC H OFF " PD 90 PRINT "PRESS X TO CONTINUE" MB 100 B=PEEK( 54297) ES 110 GET B$ DF 120 IF B$="X" THEN140 EJ 130 GOTO100 MJ 140 PRINT "PRESS X TO START " FB 150 GET B$ HQ 160 IF B$="X" THEN180 PS 170 GOTO150 PR 180 REM CHECK IF LIGHT LEVEL LOWER TH AN FIRST SETTING CM 190 IF PEEK( 54297 ) <A THEN190 SP 200 REM SET DATA DIRECTION REGISTER F OR OUTPUT ED 210 POKE 56323, PEEK( 5632 3 ) OR ( 2 T0 ) CC 220 REM SET OUTPUT LINE LOGIC LOW CJ 230 POKE 56321, PEEK ( 56321 ) ANDNOT ( 2 ?0 ) HQ 240 REM CHECK IF LIGHTING LEVEL HIGHE R THAN SECOND SETTING BE 250 IF PEEK( 54297 ) >B THEN250 HQ 260 REM SET OUTPUT LINE LOGIC HIGH GD 270 POKE 56321 ,PEEK( 56321 )OR( 2T0) DG 280 REM RESET DATA DIRECTION REGISTER FOR INPUT ED 290 POKE 56323, PEEK ( 563 2 3 ) ANDNOT ( 2 T ) 138 More Ideas Program 12-2 — Atari LP 100 REM LIQHT SWITCH HS 1 1 REM FC 120 PRINT "SET LIGHT LEVEL TO SWI TCH ON" FC 130 PRINT "PRESS X TO CONTINUE" DO 140 A=PADDLE (0) LO 150 REM CHECK IF X KEY PRESSED KG 160 IF PEEK (764) =22 THEN 180 66 170 GOTO 140 NN 175 REM CLEAR LAST KEYSTROKE DB 180 POKE 764, 255 HF 190 PRINT "SET LIGHTING LEVEL TO SWITCH OFF" FA 200 PRINT "PRESS X TO CONTINUE" DN210 B = P ADDLE ( ) Lfl 220 REM CHECK IF X KEY PRESSED KD 230 IF PEEK(764)=22 THEN 260 6C 240 GOTO 210 NH 250 REM CLEAR LAST KEYSTROKE DA 260 POKE 764,255 EI 262 PRINT :PRINT "PRESS X TO STAR T" LC 264 IF PEEK(764)=22 THEN 268 HD 266 GOTO 264 01 268 POKE 764, 255 LE270 REM CHECK IF LIGHT LEVEL LOWE R THAN FIRST SETTING JK 280 IF PADDLE ( ) < A THEN 280 SD290 REM SET DATA DIRECTION REG 1ST ER FOR OUTPUT FM 300 POKE 54018,48 IL310 POKE 54016,255 FJ 320 POKE 54018,52 FL 330 REM SET DATA LINES LOGIC LOW CC 340 POKE 54016,0 PD 350 REM CHECK IF LIGHTING LEVEL H IGHER THAN SECOND SETTING JN 370 IF PADDLE (0)>B THEN 370 10 380 REM SET DATA LINES LOGIC HIGH JD 390 POKE 54016,255 AH 400 REM RESET DATA LINES FOR INPU T FO410 POKE 54018,48 CB 420 POKE 54016,0 FL 430 POKE 54018,52 139 CHAPTER 12 Enter and run the appropriate version of Program 12-2. You'll be prompted to set the lighting condi- tion which will indicate that the switch is to turn on. Do this by exposing the analog light sensor to the amount of light at which you want the light to turn itself on. While the sensor is still exposed to this light level, press the X key on the computer. The computer stores this level of light as a num- ber and will turn on the electric light when the sensor sees less than this amount of light. The program also prompts you to set the light off condition. After the electric light has been turned on, when this second light level (or more light) is present, the electric light is turned off. Using this circuit requires that the sensor be mounted near a window where it can detect out- side light. Whatever you do, don't mount the sensor be- neath the electric light you're controlling. Multiplexer Circuit A multiplexer circuit lets your computer monitor many digital input signals using its limited num- ber of I/O lines. To make an eight-input multi- plexer, you'll have to have these components: Part Quantity Part Number 2 9-pin D-subminiature female 276-1538 (only one necessary for VIC and Atari) 1 74LS151 IC None 1 IK ohm resistor 271-8023 (not required for Atari) 1 Solderless breadboard 276-175 140 More Ideas CHAPTER 12 Follow these steps to put together your multiplexer: 1. Insert the 74LS151 IC so that its pin 1 goes into point F2 of the solderless breadboard, and its pin 9 into point E9. 2. Solder a 4-inch-long wire to pin 1 of one of the 9-pin plugs (for the Atari and VIC-20 versions, solder this wire to pin 6 of the single 9-pin plug required). This wire carries the selected data line's signal to the computer. 3. Connect the other end of this wire to point J12 of the breadboard. 4. The IK ohm resistor bridges the points HI 2 to H6 of the board. (When building the Atari ver- sion, use a jumper wire in place of the resistor.) 5. Solder wires about four inches long to pins 1, 2, 3, 7, and 8 of the second 9-pin plug (in the case of the Atari and VIC versions, solder these wires to the same pins of the single 9-pin plug). 6. The wires from pins 7 and 8 provide the power to the circuit. Connect the wire from pin 7 to point XI, and the wire from pin 8 to location Yl of the board. 7. The wires from pins 1, 2, and 3 insert into plug points D7, D8, and D9 respectively. These last three pins are used to select the data line signal "seen" by the computer. 8. Connect jumper wires as follows: Jumper From To 1 Y9 J9 2 X2 A2 3 G8 G9 Pins 1-4 and 12-15 of the 74LS151 IC are the input lines of the multiplexer. They can be con- nected to any sensor which provides an on/off signal. The sensors may be electronic (like the dig- ital light sensor) or simply switches between the pins and ground. 142 More Ideas Figure 1 2-5. Multiplexer Still Life • • » » - * >>•'*'•'<'' ' , , « » ■ ■ S - . . A congregation of wires from the multiplexer lead off to various digital sensors. If you've built a multiplexer for the Commodore 64 or Commodore 128, the 9-pin plug with one wire attached is inserted into control port 2. The other 9-pin connector plugs into control port 1. Since you used only one 9-pin plug for the Atari version, insert it into control port 2. Program 12-3 allows the circuit to monitor eight digital inputs. It outputs three digital signals to the multiplexer circuit, which tell it to route one of the input signals to a pin of the computer's I/O port. The program sequentially selects each of the eight input lines and checks its condition. (This is called polling.) If any of the eight inputs is at a logic low state, the computer prints out such a message on the screen. Program 1 2-3 — Commodore 64/1 28 PK 10 PRINT "PRESS X TO EXIT PROGRAM " GM 20 REM SET DATA DIRECTION REGISTER FO R OUTPUT QJ 30 POKE 56322,255 RP 40 FOR 1=0 TO 7 143 CHAPTER 12 PE 50 REM SET DATA OUTPUT SR 60 POKE 56320,1 RG 70 IF (PEEK(56321)AND(2T0) )=0 THEN PR INT " SENSOR ";I RK 80 NEXT I EP 90 REM RESET DATA LINES FOR INPUT RQ 100 POKE 56322,0 ES 110 GET B$ BX 120 IF B$="X" THEN END CP 130 GOTO30 Program 12-3— VIC-20 CM 10 PRINT " MONITORING SENSORS" HR 20 PRINT "PRESS X TO EXIT" DP 30 REM SET DATA DIRECTION REGISTER FO R OUTPUT QH 40 POKE 37139, ( 2 T 2+2 T 3 + 2 T 4 ) GM 50 FOR 1=0 TO 7 SP 60 REM SET DATA OUTPUT GH 70 POKE 37137,1*4 QC 80 IF (PEEK( 37137 )AND( 2T5) )=0 THEN PR INT " SENSOR ";I JM 90 NEXT I GJ 100 POKE 37139,128 ES 110 GET B$ BX 120 IF B$="X" THEN END MQ 130 GOTO40 GM 140 PRINT "TURN SWITCH OFF" Program 12-3 — Atari ME 100 REM MULTIPLE INPUTS JG110 PRINT "MONITORINB SENSORS " ON 120 PRINT :PRINT " PRESS X TO EXIT II FN 130 REM SET DATA DIRECTION RESIST ER FOR OUTPUT FO 140 POKE 54018, 48 CI 150 POKE 54016, 7 FL 160 POKE 54018, 52 DB 170 REM CYCLE THROUGH OUTPUT COMB I NAT I ON Bfl 180 FOR 1=0 TO 7 DO 190 POKE 54016, I AF 195 FOR J=l TO 10:NEXT J EH 200 IF (STRie(0)=0> THEN PRINT " S ENSOR " ; I 144 More Ideas LL210 REM CHECK IF X KEY PRESSED KB 220 IF PEEK (764) =22 THEN 250 BN 230 NEXT I BH 235 GOTO 180 NG 240 REM CLEAR LAST KEYSTROKE CP 250 POKE 764,255 AL 260 REM RESET DATA LINES FOR INPU T GC 270 POKE 54018,48 CF 280 POKE 54016,0 FP 290 POKE 54018,52 A Demultiplexer Circuit A demultiplexing circuit can be made using a 74LS154 IC. This chip takes four input signals from the computer to output a signal to one of 16 lines. The output line corresponding to the input signal combination goes logic low, while the other output lines of this IC remain high. Quantity Part 1 9-pin D-subminiature female 1 74LS154 IC 1 Solderless breadboard Part Number 276-1538 None 276-175 You'll also need some solid copper wire for jumpers and some stranded copper wire for other connections. 1. Insert the 74LS154 IC so that its pin 1 goes into point G6 of the solderless breadboard, and its pin 24 into point C6. 2. Solder wires about four inches long to pins 1, 2, 3, and 4 of the 9-pin plug. 145 CHAPTER 12 These wires connect to the breadboard at these locations: Wire from Pin To Point 1 A7 2 A8 3 A9 4 A10 3. Solder two wires to pins 7 and 8 of the 9-pin plug. Connect the wire from pin 7 to point XI, and the wire from pin 8 to location Yl of the board. 4. Solder wires for the digital output lines to these points on the breadboard: Digital Output Line To Point J6 1 J7 2 J8 3 J9 4 J10 5 Jll 6 J12 7 J13 Digital Output Line To Point 8 J14 9 J15 10 J16 11 A17 12 A16 13 A15 14 A14 15 A13 5. Connect jumper wires as follows: Jumper From To 1 Y17 J17 2 X6 A6 3 A12 Y20 4 Bll B12 146 More Ideas CHAPTER 12 When you've finished, plug the 9-pin plug into control port 2. The 74LS154 is interfaced to the computer using four lines from the control port. These four lines output the signals that select which of the output lines goes logic low. The outputs from the de- multiplexer can be used to turn on electronic switches or other devices which require digital sig- nals. The power for the demultiplexer circuit, as for the multiplexer, is obtained from pins 7 and 8 of the computer's control port. Sending signals to set an output line of the demultiplexer is very similar to sending the output required from the computer to select an input line of the multiplexer. The only difference is that four output lines from the computer are used instead of three. Try writing a program which will sequen- tially set each of the demultiplexer's output lines to a logic low state. You can verify your program using your logic probe. 148 CHAPTER 13 Robotics Robotics One of the most exciting applications of digital electronics and computers is robotics. While a ro- botics control system is beyond the scope of this book, what you'll find here are some ideas to get you started. The actions of most robots are carried out by motors. To move, for instance, a mobile robot's wheels are turned; when a robot's arm goes up, the arm's joints are moved by motors. These mo- tors, in turn, are controlled by a computer. The computer is programmed to turn the motors on and off so that the robot moves in a coordinated fashion to perform a task. You already have enough expertise to control a dc motor with your computer. You can simply switch it on and off by using an electronic switch circuit. If you use a second electronic switch cir- cuit, with a DPDT relay in place of the SPDT, you can control a dc motor to turn in both directions. Though you've already built an electronic switch circuit in Chapter 8, it will be easier if you just begin from scratch when putting together a dc motor control circuit. Here's what you'll need: Part Quantity Part Number 1 9-pin D-subminiature female 276-1538 2 2N2222 NPN transistors 276-1617 2 2.2K ohm resistors 271-8027 2 IN914 diodes 276-1620 1 5 -volt SPDT DIP relay 275-243 1 DPDT DIP relay 5 -volt coil 275-215 1 Solderless breadboard 276-175 151 CHAPTER 13 c o I © o o E E o O D O D i "g b o n ~o o o m o O Q CO © b * *, 60 n c S 3 H 3 D- &. Robotics Part Quantity Part Number 1 7400 IC (Atari) 276-1801 1 DC battery-powered motor None You'll also need some solid copper wire for con- nections to the 9-pin plug, motor, and battery, as well as for jumpers on the solderless breadboard. If you're building the Atari version of the con- trol circuit, you'll need a longer than normal solderless breadboard. The Commodore Version Here's how to build the Commodore version of the dc motor control circuit. 1. Wire the 9-pin plug. Cut four pieces of wire, each about four inches long, and remove about 1/4 inch of the insulation from the wires' ends. 2. Solder wires to pins 1, 2, 7, and 8 of the 9-pin plug. 3. Connect the four wires as follows: The wire from pin 8 connects to point Yl on the solder- less breadboard. The wire from pin 7 connects to point XI of the solderless breadboard. The last two lines, from pins 1 and 2, connect to locations A3 and A6 respectively. 4. Connect the two 2.2K ohm resistors between points C3 and F3, and points C6 and F6 on the solderless breadboard. 5. Mount one 2N2222 transistor so that its base inserts into point H3, its emitter into point H2, and its collector into point H3. 6. The second 2N2222 transistor should be mounted so that its base inserts into location H6, its emitter into point H7, and its collector into H5. 153 CHAPTER 13 7. The first diode is connected so that its cathode lead inserts into point X4 of the solderless breadboard and its anode lead connects to point A4. (A band around one end of the di- ode is generally used to identify the cathode lead.) 8. The second diode should be placed so that its cathode lead goes into location X7, while its anode lead connects to point A7. 9. The SPDT relay is inserted so that its normally open and normally closed pins attach to points F9 and E9 respectively. The common pin con- nects to point E14. Its coil terminal should be connected to points E10 and F10. 10. Insert the DPDT relay so that its normally open pins 1 and 2 attach to points E23 and F23 respectively. Its normally closed pins 1 and 2 should be connected to points E21 and F21 respectively. The two common pins, 1 and 2, are attached to locations E19 and F19. Fi- nally, the coil terminal is connected to points E16 and F16. 11. The following jumper connections are required: Wire From To 1 X10 A10 2 X16 A16 3 E4 F4 4 E7 F7 5 A21 J23 6 A23 J21 7 H9 H19 8 14 110 9 J7 J16 10 J2 Y2 11 J5 Y4 12. Solder two wires to the battery you'll use, one wire to the positive pole, the other to the neg- ative pole. 154 Robotics 13. Connect the positive pole wire to point 123 of the solderless breadboard. Connect the nega- tive pole wire to point B23. 14. Solder two wires to the dc motor, one to its positive pole, the other to its negative pole. 15. Connect the positive pole wire to point A19 of the breadboard and the negative pole wire to location A14. Figure 1 3-2. The Finished Commodore Board This solderless breadboard contains the most complex circuit project in this book. Changes When Constructing the Atari Version Refer to Figure 13-3 for the layout of the Atari version. Substitute the following steps in the Atari version: 3. The wires from pins 1 and 2 connect to points J25 and A26 respectively. 155 CHAPTER 13 Robotics 11. These are the jumper connections for the Atari version: 147' - Wire From To i vi n X10 A10 2 Xl6 A16 3 b4 F4 4 fc.7 prj F7 5 B3 G30 6 B6 B31 7 D26 C27 8 D28 D29 9 C29 D30 10 H25 G26 11 G27 G28 12 H28 G29 13 A21 J23 14 A23 J21 15 J31 Y31 16 H9 H19 17 14 110 18 J7 J16 19 J2 Y2 20 J5 Y4 13. Connect the positive pole wire from the bat- tery to point 123 of the solderless breadboard. Connect the negative pole wire to point 121. 16. Insert the 7400 IC into the solderless bread- board so that its pins 1 and 8 go into plug points F25 and E31 respectively. Warning: If you use a larger motor, remember to mind the ratings of the solderless breadboard and its relays. The circuit uses two signals from the com- puter — one to switch on the motor and the other to reverse the battery polarity to the motor. Re- versing the battery polarity to a dc motor causes its shaft to rotate in the opposite direction. The motor can be used to turn the wheels of a small mobile "turtle" robot. If you use a dc gear motor with a reasonably low rpm speed and enough torque, you can even control a joint of a 157 CHAPTER 13 robot, such as the elbow or shoulder of a mechan- ical arm. You can use several of these motor con- trol circuits to operate a multijoint robot. Consider using a demultiplexer to send the digital signals to different motor control circuits. Some robots simply turn on their motors for a certain amount of time, assuming that the parts manipulated by the motors reach particular points. But if, for example, something obstructs their movements, these robots continue working, oblivi- ous to their situations. More intelligent robots use sensors to inform them about their environments. If you build a mobile robot, you can use micro- switches to check whether your robot has bumped into a wall. If it requires several such sensors, you may have to use a multiplexing circuit. You can also mount potentiometers to turn with the joints of a mechanical-arm robot. The values returned by the A/D converter of your computer allow you to keep track of the arms' positions. Once you build the motor control circuit, you can control it from your computer in much the same way as the following demonstration program does. Plug the circuit into control port 1 of your computer. (The Commodore 64/128 version of the program requires that you insert a joystick into control port 2.) Program 1 3-1 — Commodore 64/1 28 AK 100 REM MOTOR CONTROL DEMONSTRATION SS 110 REM REQUIRES A JOYSTICK HC 115 PRINT "JOYSTICK CONTROLS " : PRINT SA 120 PRINT "UP - MOTOR TURNS IN ONE DIR ECTION " CH 130 PRINT "DOWN - MOTOR TURNS IN OPPOS ITE DIRECTION" CE 132 PRINT : PRINT "PRESS FIRE BUTTON TO I SPACE] EX IT DEMO" DB 135 B=0 HK 140 A=PEEK( 56320) CG 150 IF (A AND 2T0)=0 THEN GOSUB 1000: GOTO 140 158 Robotics EP 160 IF (A AND 2TD=0 THEN GOSUB 2000: GOTO 140 CQ 170 GOSUB 3000 PM 180 IF (A AND 2T4)=0 THEN END JX 190 GOTO 140 CB 1000 REM TURN MOTOR ON IN ONE DI RECTI ON CM 1010 REM CHECK IF THIS HAS ALREADY BE EN DONE FK 1020 IF B=l THEN 1100 MA 1030 REM SET FIRST DATA LINE FOR OUTP UT SM 1040 POKE 56323, PEEK ( 56323 ) OR ( 2 T0 ) GD 1050 REM SET FIRST DATA LINE LOGIC LO W TO TURN ON MOTOR EG 1060 POKE 56321, PEEK( 56321 )ANDNOT(2T0 ) KD 1070 B=l RF 1100 RETURN JJ 2000 REM TURN ON MOTOR IN OTHER DIREC TION KJ 2010 REM CHECK IF THIS HAS ALREADY BE EN DONE KK 2020 IF B=2 THEN 2100 CR 2030 REM SET BOTH DATA LINES FOR OUTP UT QX 2040 POKE 56323, PEEK( 56323 )OR( 2T0+2T1 ) CM 2050 REM SET BOTH DATA LINES LOGIC LO W TO TURN ON MOTOR AND REVERSE P OLARITY MQ 2060 POKE 56321, PEEK ( 563 21 ) ANDNOT ( 2 T0 + 2U) RC 2070 B=2 MC 2100 RETURN MC 3000 REM TURN MOTOR OFF EC 3010 REM CHECK AND SEE IF THIS HAS BE EN DONE JP 3020 IF B=0 THEN 3100 KM 3030 REM TURN BOTH DATA LINES LOGIC H IGH BM 3040 POKE 56321, PEEK(56321)OR(2T0+2Tl ) SG 3050 REM RESET BOTH DATA LINES FOR IN PUT PX 3060 POKE 56323, PEEK( 56323 ) ANDNOT ( 210 + 2TD XS 3070 B=0 HA 3100 RETURN 159 CHAPTER 13 Program 13-1— VIC-20 XS 10 PRINT "KEYBOARD CONTROLS ": PRINT SB 20 PRINT "< - MOTOR TURNS IN ONE DIREC TION" KR 30 PRINT "> - MOTOR TURNS IN OPPOSITE [SPACE } DIRECTION" DE 40 PRINT: PRINT "PRESS SPACE BAR TO EXI T DEMO" CH 50 B=0 EH 60 A=PEEK(197) MS 70 IF A=29 THEN GOSUB1 20 : GOTO60 PS 80 IF A=37 THEN GOSUB210 :GOTO60 MK 90 GOSUB300 XD 100 IF A=32 THEN POKE 198,0:END CP 110 GOTO60 FJ 120 REM TURN MOTOR ON IN ONE DIRECTIO N PP 130 REM CHECK IF THIS HAS ALREADY BEE N DONE SE 140 IF B=l THEN200 XK 150 REM SET FIRST DATA LINE FOR OUTPU T FJ 160 POKE 37139, PEEK ( 37 1 39 ) OR ( 2 T 2 ) CS 170 REM SET FIRST DATA LINE LOGIC LOW TO TURN ON MOTOR RF 180 POKE 37137, PEEK(37137)ANDNOT(2T2) FF 190 B=l MC 200 RETURN JQ 210 REM TURN ON MOTOR IN OTHER DIRECT ION QR 220 REM CHECK IF THIS HAS ALREADY BEE N DONE QC 230 IF B=2 THEN290 PR 240 REM SET BOTH DATA LINES FOR OUTPU T PR 250 POKE 37139, PEEK ( 37 1 39 ) OR ( 2 T 2+ 2 T 3 ) PX 260 REM SET BOTH DATA LINES LOGIC LOW TO TURN ON MOTOR AND REVERSE POL ARITY AG 270 POKE 3 7137 , PEEK ( 37137 ) ANDNOT ( 2 T 2+ 2T3) MM 280 B=2 SK 290 RETURN RP 300 REM TURN MOTOR OFF CR 310 REM CHECK AND SEE IF THIS HAS BEE N DONE EG 320 IF B=0 THEN380 BM 330 REM TURN BOTH DATA LINES LOGIC HI GH 160 Robotics QQ 340 POKE 37137 f PEEK(37137)OR(2T2+2T3) FH 3 50 REM RESET BOTH DATA LINES FOR INP UT CQ 360 POKE 37139,PEEK(37139)ANDNOT(2T2+ 2T3) KX 370 B=0 HS 380 RETURN Program 13-1 — Atari AO 100 REM MOTOR CONTROL DEMONSTRAT I ON NF110 PRINT "KEYBOARD CONTROL" Cft 120 PRINT BF130 PRINT "< - MOTOR TURNS IN ONE DIRECTION" KJ 140 PRINT "> - MOTOR TURNS IN OPP OSITE DIRECTION" LO 150 PRINT "S - STOP MOTOR " AK 155 PRINT :PRINT "X - EXIT PROBRA M" EB 160 B = CN 170 A = PEEK (764) IK 180 IF A = 54 THEN GOSUB 1000:BOTO 170 IN 190 IF A = 55 THEN BOSUB 2000:BOTO 170 NF 200 GOSUB 3000 AK210 IF A = 22 THEN END 6F 220 SOTO 170 06 1000 REM TURN MOTOR ON IN ONE DIR ECTION OJ 1010 REM CHECK IF THIS HAS ALREAD Y BEEN DONE PD 1020 IF B=l THEN 1100 AB 1030 REM SET DATA LINES FOR OUTPU T IP 1032 POKE 54018, 48 FG 1034 POKE 54016, 3 10 1036 POKE 54018,52 NJ 1040 REM SET FIRST DATA LINE LOGI C LOW TO TURN ON MOTOR FD 1050 POKE 54016, 2 HH 1060 B=l KC 1 100 RETURN NH2000 REM TURN ON MOTOR IN OTHER D IRECTION OK 2010 REM CHECK IF THIS HAS ALREAD Y BEEN DONE 161 CHAPTER 13 PS 2020 IF B = 2 THEN 2100 CP 2030 REM SET BOTH DATA LINES FOR OUTPUT JA 2032 POKE 54018,48 FH 2034 POKE 54016,3 IP 2036 POKE 54018,52 DF 2040 REM SET BOTH DATA LINES L06I C LOW TO TURN ON MOTOR AND R E VERSE POLARITY FC 2050 POKE 54016,0 HJ 2060 B = 2 KD2100 RETURN FN 3000 REM TURN MOTOR OFF JJ3010 REM CHECK AND SEE IF THIS HA S BEEN DONE PS 3020 IF B = THEN 3100 JD 3030 REM SET BOTH DATA LINE LOGIC HIGH FF 3040 POKE 54016,3 DL 3050 REM RESET DATA LINES FOR INP UT JC 3060 POKE 54018,48 FF 3070 POKE 54016,0 JA 3090 POKE 54018,52 IA 3095 B = KE3100 RETURN 162 Appendices COMPUTE !'s Guide to Typir iy ill r i uyivji i lo Computers are precise — type each program in this book exactly as it's listed, including the necessary punctuation and symbols, except for special char- acters noted below. We've provided a special list- ing convention as well as a program to check your typing — "The Automatic Proofreader." Programs for Commodore and Atari 800/XL/XE computers may contain some hard-to-read special characters, so we have a listing system which indi- cates these control characters. You'll find these Commodore and Atari characters in curly braces; do not type the braces. For example, {CLEAR} or {CLR} instructs you to insert the symbol which clears the screen on the Atari or Commodore ma- chine. A complete list of these symbols is found in the table below. For Commodore and Atari com- puters, a single symbol by itself within curly braces is usually a control key or graphics key. If you see {A}, hold down the CONTROL key and press A. This will produce a reverse video charac- ter on the Commodore (in quote mode) or a graphics character on the Atari. Graphics characters entered with the Commo- dore logo key are enclosed in a special bracket: f<A>]. In this case, you would hold down the Commodore logo key as you type A. Our Com- modore listings are in uppercase, so shifted sym- bols are underlined. A graphics heart symbol (SHIFT-S) would be listed as S. One exception is {SHIFT-SPACE}. When you see this, hold down SHIFT and press the space bar. If a number pre- cedes a symbol, such as {5 RIGHT}, {6 S}, or f<8 Q>], you would enter five cursor rights, six shifted S's, or eight Commodore-Q's. On the 165 APPENDIX A When You Read: {CLR} {HOME} {UP} {DOWN} {LEFT} {RIGHT} {RVS} {OFF} {BLK} {WHT} {RED} {CYN} {PUR} {GRN} {BLU} {YEL} Atari, inverse characters (white on black) should be entered with the inverse video key (Atari logo key on 400/800 models). Press: SHIFT CLR/HOME CLR HOME SHIFT t CRSR J t CRSR i SHIFT «— CRSR — — CRSR- CTRL CTRL CTRL CTRL CTRL CTRL CTRL CTRL CTRL CTRL See: m □ m □ When You Read: & 3 2 i 4 § & *3 g 7§ ! Fl } { n } { F3 } { F4 } { re } { F6 } { F7 } { F8 } Press: COMMODORE COMMODORE COMMODORE COMMODORE COMMODORE COMMODORE COMMODORE COMMODORE SHIFT SHIFT SHIFT SHIFT See: EH BIB Bffl 00 E Ell □ ■ ■ ■ Whenever more than two spaces appear in a row, they are listed in a special format. For ex- ample, {6 SPACES} means press the space bar six times. Our Commodore listings never leave a sin- gle space at the end of a line, instead moving it to the next printed line as {SPACE}. The Automatic Proofreader Type in the appropriate program listed below, then save it for future use. The Commodore Proofreader works on the Commodore 128, 64, 166 COMPUTE! 's Guide to Typing In Programs and VIC-20. Don't omit any lines, even if they contain unfamiliar commands or you think they don't apply to your computer. When you run the program, it installs a machine language program in memory and erases its BASIC portion automati- cally (so be sure to save several copies before run- ning the program for the first time). If you're using a Commodore 128, do not use any GRAPHIC commands while the Proofreader is ac- tive. You should disable the Commodore Proof- reader before running any other program. To do this, either turn the computer off and on or enter SYS 64738 (for the 64), SYS 65341 (128), or SYS 64802 (VIC-20). To reenable the Proofreader, re- load the program and run it as usual. Unlike the original VIC/64 Proofreader, this version works the same with disk or tape. On the Atari, run the Proofreader to activate it (the Proofreader remains active in memory as a machine language program); the BASIC loader automatically erases itself. Pressing SYSTEM RE- SET deactivates the Atari Proofreader; enter PRINT USR(1536) to reenable it. Once the Proofreader is active, try typing in a line. As soon as you press RETURN, a pair of let- ters appears. The pair of letters is called a checksum. Compare the value displayed on the screen by the Proofreader with the checksum printed in the program listing in the book. The checksum is given to the left of each line number. Just type in the program a line at a time (without the printed checksum), press RETURN or Enter, and compare the checksums. If they match, go on to the next line. If they don't, check your typing; you've made a mistake. Because of the checksum method used, do not type abbreviations, such as ? for PRINT. On the Atari Proofreader, spaces are not counted 167 APPENDIX A as part of the checksum, so be sure you type the right number of spaces between quotation marks. The Atari Proofreader does not check to see that you've typed the characters in the right order, so if characters are transposed, the checksum still matches the listing. The Commodore Proofreader catches transposition errors and ignores spaces un- less they're enclosed in quotation marks. Program 1 . Commodore Proofreader 10 VEC=PEEK(772)+256*PEEK(773) :LO=43 :HI=44 20 PRINT" { CLR} I WHT J AUTOMATIC PROOFREADER FOR ";:IF VEC=42364 THEN PRINT "C-64" 30 IF VEC=50556 THEN PRINT "VIC-20 { BLU } " 40 IF VEC=35158 THEN WAIT CLR: PRINT "PLUS / 4 & 16" 50 IF VEC=17165 THEN LO=45 :HI=46 :WAIT CLR:PRINT"12 8 1 WHT j " 60 SA=(PEEK(LO)+256*PEEK(HI ) )+6:ADR=SA 70 FOR J=0 TO 166: READ BYT: POKE ADR, BYT : ADR=ADR+1 : CHK=CHK+BYT :NEXT 80 IF CHK<> 20570 THEN PRINT "*ERROR* CHECK TYPING I SPACE j IN DATA STATEMENTS ": END 90 FOR J=l TO 5 : READ RF, LF, HF : RS=SA+RF :HB=INT ( RS/2 56) :LB=RS-(256*HB) 100 CHK=CHK+RF+LF+HF : POKE SA+LF, LB : POKE SA+HF , HB : N EXT 110 IF CHKO22054 THEN PRINT "* ERROR* RELOAD PROGR AM AND CHECK FINAL LINE": END 120 POKE SA+149, PEEK (772) : POKE SA+150 , PEEK ( 77 3 ) 130 IF VEC=17165 THEN POKE SA+14 , 22 : POKE SA+18,23: P0KESA+29 , 224 : POKESA+1 39 , 2 24 140 PRINT CHR$ ( 147 ) ;CHRS (17 ); "PROOFREADER ACTIVE": SYS SA 150 POKE HI , PEEK ( HI ) +1 : POKE ( PEEK ( LO ) +256*PEEK ( HI ) )-l,0:NEW 160 DATA 120,169,73,141,4,3,169,3,141,5,3 170 DATA 88,96,165,20,133,167,165,21,133,168,169 180 DATA 0,141,0,255,162,31,181,199,157,227,3 190 DATA 202,16,248,169,19,32,210,255,169,18,32 200 DATA 210,255,160,0,132,180,132,176,136,230,180 210 DATA 200,185,0,2,240,46,201,34,208,8,72 220 DATA 165,176,73,255,133,176,104,72,201,32,208 230 DATA 7,165,176,208,3,104,208,226,104,166,180 240 DATA 24,165,167,121,0,2,133,167,165,168,105 250 DATA 0,133,168,202,208,239,240,202,165,167,69 260 DATA 168,72,41,15,168,185,211,3,32,210,255 168 COMPUTE! 's Guide to Typing In Programs 270 DATA 104,74,74,74,74,168,185,211,3,32,210 280 DATA 255,162,31,189,227,3,149,199,202,16,248 290 DATA 169,146,32,210,255,76,86,137,65,66,67 300 DATA 68,69,70,71,72,74,75,77,80,81,82,83,88 310 DATA 13,2,7,167,31,32,151,116,117,151,128,129, 167,136,137 Program 2. Atari Proofreader 100 GRAPHICS 110 FOR 1=1536 TO 1700:READ A : POKE I,A:CK=CK +A: NEXT I 120 IF CKO19072 THEN ? "Error in DATA State ments. Check Typing. ":END 130 A=USR<1536) 140 ? :? "Automatic Proofreader Now Activate d. " 150 NEW 1536 DATA 104,160,0,185,26,3 1542 DATA 201,69,240,7,200,200 1548 DATA 192,34,208,243,96,200 1554 DATA 169,74,153,26,3,200 1560 DATA 169,6,153,26,3,162 1566 DATA 0,189,0,228,157,74 1572 DATA 6,232,224,16,208,245 1578 DATA 169,93,141,78,6,169 1584 DATA 6,141,79,6,24,173 1590 DATA 4,228,105,1,141,95 1596 DATA 6,173,5,228,105,0 1602 DATA 141,96,6,169,0,133 1608 DATA 203,96,247,238,125,241 1614 DATA 93,6,244,241,115,241 1620 DATA 124,241,76,205,238,0 1626 DATA 0,0,0,0,32,62 1632 DATA 246,8,201,155,240,13 1638 DATA 201,32,240,7,72,24 1644 DATA 101,203,133,203,104,40 1650 DATA 96,72,152,72,138,72 1656 DATA 160,0,169,128,145,88 1662 DATA 200,192,40,208,249,165 1668 DATA 203,74,74,74,74,24 1674 DATA 105,161,160,3,145,88 1680 DATA 165,203,41,15,24,105 1686 DATA 161,200,145,88,169,0 1692 DATA 133,203,104,170,104,168 1698 DATA 104,40,96 169 B Integrated Circuits 7400/74LS00 Quad NAND Gate Ground 7 n 14 +5 volts 13 12 11 10 171 APPENDIX B 7402/74LS02 Quad NOR Gate —zj— ^ — TL_n] 14 +5 volts 13 10 172 ated Circuits 7404/74LS04 Hex Inverter Ground 7 I 8 173 APPENDIX B 7408/74LS08 Quad AND Gate Ground 7 "U 14 13 12 11 10 + 5 volts 174 integrated Circuits 175 APPENDIX B 74151/74LS151 Eight Line to One Line Mutliplexer Input 3 1 16 + 5 volts Input 2 2 15 Input 4 Input 1 3 14 Input 5 Input 4 13 Input 6 Output 5 12 Input 7 Inverted output 6 11 Enable 7 10 B > In P ut f select Ground 8 9 176 Integrated Circuits 74154/74LS154 Four Line to 16 Line Demultiplexer Output 1 24 + 5 volts Output 1 2 23 " Output 2 3 22 V Output / select Output 3 4 21 Output 4 5 20 V Output 5 6 19 Enable 2 Output 6 7 18 Enable 1 Output 7 8 17 Output 15 Output 8 9 16 Output 14 Output 9 10 15 Output 13 Output 10 11 14 Output 12 Ground 12 13 Output 11 177 APPENDIX B 74367/74LS367 Hex Three-State Buffers Enable input Ground 8 16 15 14 13 12 11 10 -1-5 volts Enable input Truth Table Enable Input Input Output H H or L High impedance L L L L H H 178 ntegrated Circuits 179 Index actuators vii 97 A/D converter 33 analog circuit 3 analog devices 33 analog-to-digital converter. See A/D converter applications vii Atari BASIC 83 "Automatic Proofreader, The" 166-69 binary number system 3-6 bit 5 Boolean algebra 109 breadboarding viii. See also wiring, methods of burglar alarm 97-106 Atari program 105 Commodore program 102 constructing 99-100 VIC-20 program 103 byte 6 circles, small 110 circuit, analog 3 circuit, building a viii circuit, digital 3 cold joint xii control port pin 82, 109 data vii data direction register 81, 82 Atari 82-83 Commodore 81-82 data port 81 dc motor control circuit 151 Atari program 161-62 Commodore program 158-59 constructing (Atari version) 155-57 constructing (Commodore version) 153-55 VIC-20 program 160-61 decoders 115-18 demultiplexer 115-18, 158 demultiplexer circuit 145-48 constructing 145-46 digital circuitry 109 digital light beam timer 74-78 Atari program 78 Commodore program 76 VIC-20 program 77 digital light sensor 97, 98, 129 variable 67 digital logic 109-20 digital signal 67, 109 high 67 low 67 D-subminiature female connectors 9 electromagnet 90 electromechanical switch 90 electron beam 59-61 electron gun 53 electronic signals 81 electronic switch 81-94, 98, 136 Atari program 93 Commodore program 92 constructing 84-88 using 91, 94 VIC-20 program 92 electrons 53 encoders 115-18 game paddles 33-41 Atari program 39 Commodore program 38 constructing 34-35 "ML Paddle Reader" program 41 reading 39-40 VIC-20 program 39 gates 109-15 AND 111 combining 143 exclusive NOR 113 exclusive OR 112 NAND 111 nonin verting buffer 110 NOR 112 NOT 110 OR 112 H (logic high) 110 IC chip. See integrated circuit chip icons xiii input 18 input/output ports 9 integrated circuit chip xi, 118 pins 54 integrated circuits 171-79 demultiplexer, four line to 16 line 177 hex inverter 173 hex three-state buffers 1 78 multiplexer, eight line to one line 176 quad AND gate 174 quad NAND gate 171 quad NOR gate 172 quad operational amplifier 179 quad OR gate 175 interrupt request (IRQ) 39 inverters 110 I/O pin 82 I/O ports 9 181 IRQ. See interrupt request joystick 97 constructing 23-29 gravity 28-29 port 9-11 push button 23-27 push button, constructing 24-27 joystick port connector 16-20 Atari program 19 Commodore program 18 constructing 16-17 VIC-20 program 19 L (logic low) 100 light-emitting diode (LED) 12, 91 light pen 53-64, 67 Atari program 64 Commodore program 62 constructing 54-58 programming with 61-62 VIC-20 program 63 light sensor, analog 45-50, 136 Atari program 49 Commodore program 49 constructing (Atari version) 47-48 constructing (Commodore version) 45-47 light sensor, digital 67-78 Atari program 73 Commodore program 73 constructing 68-71 VIC-20 program 73 light switch 136-40 Atari program 139 Commodore program 137 VIC-20 program 138 location 83 logic probe 10-13, 123-26 constructing 10-13, 123-25 using 126 logic states high 15 low 15, 20 low-power Schotkey (LS) 120 "ML Paddle Reader" program 41 monitor 53 multiplexer circuit 140-45, 158 Atari program 144 Commodore program 143 constructing 142 VIC-20 program multiplexers 115-18 multiplier 13 NAND gates 60 noninverting buffer 60, 90 number systems 4-6 binary 3-6 decimal 4 ohms 13 output 18 output signal 109 PADDLE(X) 34, 50 phototransistor 60, 72 polling 143 ports 9, 10 data 81 input/output 9 joystick 9-11 potentiometer 33 power ratings 14 registers 81 resistor color codes 14 resistors 13, 14, 33, 126 resistor variable 45 robotics 151-62 sensors vii, 81, 97, 109 software vii soldering 55 soldering iron, heating ix-xii STICK 18, 74, 82 STRIG 18 switch 3, 72 Atari version 169 Commodore version 168 tilt 28 switch sensor 98, 100 infrared 98 magnetic switch 98 metallic tape 98 ultrasonic 98 vibration detectors 98 tilt switches 28 timer circuit 74 tin xii tolerance 13 transistor-transistor logic signal level. See TTL truth table 109 TTL 3, 120 two-beam digital timer circuit 129-36 Atari program 135 Commodore program 134 constructing 130 using 134 VIC-20 program 135 typing in programs 165-69 voltage 3, 33 watts 14 wiring, methods of viii circuit boards viii mounting viii plug points ix wire wrapping viii 182 COMPUTE! Books Ask your retailer for these COMPUTE! Books or order directly from COMPUTE!. Call toll free (in US) 800-346-6767 (in NY 212-887- 8525) or write COMPUTE! Books, P.O. Box 5038, F.D.R. Station, New York, NY 10150. Quantity Title Price" Total SpeedScript: The Word Processor for the Commodore 64 and VIC-20 (94-9) $ 9.95 Commodore SpeedScript Book Disk $ 1 2.95 1 28 Machine Language for Beginners (033-5) $16.95 COMPUTEi's First Book of the Commodore 128 (059-9) $14.95 COMPUTE! 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