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Getting Going With BASIC Stamp In these days of 32-bit microprocessors handling millions of instructions per second and running at speeds in the hundreds of MHz, why on earth would anyone want to use a strange 14-bit processor which can only handle BASIC programs no bigger than 256 bytes . . . and screams along at just 2000 BASIC instructions per second? The answer is simple: because you CAN! Or is it because YOU can! To program most microprocessors you need to be an expert in machine language code. Not so with the BASIC Stamp. If you know BASIC, you should be able to program it to do, well, whatever you want to (as long as you can do it in 256 bytes!). Even if you don’t know BASIC, it’s not too hard to learn. You’d know what D-I-Y stands for, of course. Now the BASIC Stamp lets you T-I-Y (think it yourself) before you D-I-Y. But what is this BASIC Stamp, anyway? You’ve probably heard of PIC microcontrollers. Made by Microchip (USA) and intended for control use, they’re found in countless applications and sold in the millions upon millions (bet your computer mouse even has one in it!). In normal applications, they’re programmed once and that’s it. As versatile as they are for original equipment manufacturers, though, PIC chips are not particularly useful for hobbyists and experimenters; at least not in their own right. That’s where the BASIC Stamp comes in. Back in 1993, Chip Gracey (no kidding, his name is Chip!) of the US company Parallax combined a 16C56 PIC microcontroller with a 93LC56 electrically erasable PROM, loaded in a BASIC interpreter, enabled 8 input/output ports and a few other goodies... and the BASIC Stamp was born. The version of the BASIC Stamp 1 we are using is supplied as a self-contained module, housed on a tiny (36 x 10mm) PC board and terminated to a row of 14 header pins at 0.1-inch spacing. These mate with either a standard 14-pin header socket or even half of a by ROSS TESTER & BOB NICOL* 32  Silicon Chip 28-pin IC socket. Components are all surface mount types which means it’s just as well you don’t have to do any assembly (no pun intended) on the BASIC Stamp PC board. The reason it is called the BASIC Stamp is that the original design fitted onto a PC board the size of a postage stamp. Today it’s just a tiny bit larger with a few more components. Fig.1 shows the circuit diagram of the BASIC Stamp. In fact, this is slightly different to the model we are using because ours also has an onboard 5V regulator, allowing supplies of up to 15V or even higher. Because of its very low drain (1-2mA, ignoring input/output or I/O requirements), it is eminently suitable for battery operation (a 9V battery will last for weeks). In real-world applications the I/O current cannot be ignored, so a 9VDC plugpack of a few hundred milliamps or so is generally preferred. Speaking of I/O, any of the eight pins will source up to 20mA or sink up to 25mA, with the proviso of a total loading of 40mA (source) or 50mA (sink). This makes the BASIC Stamp capable of directly driving LEDs, piezo buzzers, speakers and even some sensitive relays. With buffering, of course, much more can be driven. For programming, the BASIC Stamp connects to the parallel port of any IBM-compatible personal computer running good, ol’fashioned DOS. That’s right, you don’t need Windows – 1, 2, 3, 95, 98, NT, 2000 or any other derivative. And when we say any PC, we mean any PC – here’s a good reason to fire up the old XT or 8088-based machine that’s been languishing in the garage for 10 years! (Of course, if you want to use the latest Pentium II 450, go right ahead. Better still, we’ll swap you a perfectly good XT and throw in a Sydney Harbour Bridge ...) Sure, the BASIC Stamp will only handle 256 bytes of programming (around 80-100 instructions). But in these days of long-winded and often superfluous coding, that teaches you to be efficient, even miserly! We mentioned before that it is programmed in BASIC. That’s not strictly true; it’s Parallax’s own version of BASIC called PBASIC. The structure is much the same except that lines of code are not numbered, they’re labelled. However, if you know good old garden variety BASIC (in any of its forms) you shouldn’t have too much difficulty with PBASIC. PBASIC has a suite of 33 commands. The usual BASIC ones such as GOTO, FOR-NEXT, IF and so on are there but there are a few new ones necessary for the Stamp’s role as a logic controller chip. Any command works with any I/O pin. If you don’t know BASIC, here’s the perfect opportunity to learn. It’s a lot simpler than trying to learn machine language, C or other more recent languages. (BASIC, including a detailed manual, was supplied with most computers up until about the ’386 days. If you don’t have a copy, it can be picked up for a song or even a few notes). The BASIC Stamp PC Board Having waxed eloquent about the BASIC Stamp’s features, the way it is supplied is rather inconvenient to use, not to mention risky. Taking the latter point first, the BASIC Stamp sells for around $80 yet, as far as we can tell, contains no reverse polarity protection (despite the on-board regulator). Our first reaction was how we would feel if we’d just spent eighty bucks and saw it disappear in a wisp of smoke . . . As far as incovenience goes, you obviously have to be able to interface to the microprocessor board – somehow. In the past, we’ve seen a number of designs in magazines using perforated strip board. We shudder. If you’re building up a $10 circuit, strip board might be good enough but remember, the BASIC Stamp is worth $80! To use strip board you have to cut tracks and it’s easy to miss one or more. It’s also very easy to short between tracks with copper swarf, especially using the old “big drill in small hole” track-cutting routine. No! Strip board is a definite no-no as far as we are concerned – especially for this type of project. The only logical solution was to design our own PC board which would not only accommodate the BASIC Stamp module, it would also allow us to include some other components which would make the whole thing that much more user-friendly. That includes reverse polarity protection and some on-board supply decoupling Fig.1: a somewhat simplified circuit diagram of the BASIC Stamp, with the or smoothing. actual module shown bottom right, same size. IC1 is a PIC microprocessor, Because of the previously-mennormally one-time-programmable but in this configuration receives its data from tioned limitations on the BASIC IC2, a 256-byte EEPROM (electrically erasable, programmable, read-only memory). Stamp I/O, we have included a An on-board 4MHz ceramic resonator sets operating speed. The ‘‘brownout’’ circuit ULN2003 buffer. This is a 7-way shown top left automatically resets the device if the supply falls below 4V. January 1999  33 The SILICON CHIP version of the BASIC Stamp experimenter's kit. The thicker lead ending in the DB-25 plug connects to the parallel port on any IBM-compatible PC. The thin lead is for power – in this case a 9VDC plugpack. The close-up photo of the PC board itself reveals a 16-way pin header (which allows connection to all BASIC Stamp pins), reverse-polarity protection diode and power supply decoupling capacitor, the BASIC Stamp module (end-on in its 14-way header socket), the ULN2003 buffer IC and a variety of input sensor devices and output devices – LDR, 10-turn trimpot, piezo buzzer, LED and DPDT relay. Also provided are plenty of I/O pads for further experimentation. open-collector Darlington driver which has a maximum collector current of 350mA or 500mA (depending on brand) for each buffer so it can drive significantly larger loads. We’ve also included a double pole change­ over (DPDT) relay, driven by one of the ULN2003 outputs. And before anyone thinks we’ve forgotten the usual suppression diode across the relay contacts, each of the ULN2003 outputs has one built in. Jumping ahead of ourselves, the ULN2003 gets quite hot – no, very o hot. But it's rated at 150 C so there's no great problem. Just thought we'd warn you in advance! There’s also a LED, an LDR, trimpot and piezo buzzer mounted on the board. These will be used in some simple programs which you can use to try out the BASIC Stamp – before you start writing your own! Into the bargain, we’ve also included some spare tracks and pads which would accommodate other components for uses as yet undreamed of. Putting it together Assembly of the PC board is very simple, as it should be with just a handful of components. Start with the PC stakes (the relay outputs) then the Parts List for Timer Projects 1 BS1-IC BASIC Stamp module with stamp1.exe operating software, PC    parallel port connection cable and    power connection cable (see text)    1 ULN2003 7-way peripheral driver 1 1N4004 or similar diode 1 LED, any type 1 1kΩ 1/4W resistor 1 20kΩ, 10-turn vertical trimpot 1 light-dependent resistor 1 100µF 25VW electrolytic capacitor 34  Silicon Chip 1 12V mini relay with DPDT contacts 1 small piezo buzzer 1 PC board, 103x55mm, coded SC11301991 1 16-way header pin set, 0.1in spacing 1 14-way header socket, 0.1in spacing 3 (or 6) PC stakes (as required) 1 plugpack supply, approx 9-12V DC <at> 400-500mA output   (to suit application) resistor, LDR, LED and diode – their pigtails will give you the wire you need for the link and the two connection wires for the piezo buzzer. It’s probably a good idea to fit the socket terminal strip and pin header next, before any of the larger components start crowding the board. The socket can go either way around. Ideally, the pin header and the sockets on the power and output leads should be marked some way so that they will never be incorrectly connected. We used some bright red nail polish to paint a red stripe on the base of the third pin in from one end of the header, and some quick-drying paint to put a stripe on the next (fourth) pin. We used yellow ’cause we had some. We painted matching stripes on the output lead socket (a red stripe on the + lead) and on the output lead socket (a yellow stripe on the end of the socket with the green wire attached. In retrospect, green would have been a better colour to use!). If you don’t have any paint, try coloured correction fluid. When later connecting the sockets to the pin header, it’s just a matter of connecting colour to colour. Having marked the pin header in this way, it must be mounted with the marked pins closest to the diode (the red pin, marking the positive supply, actually lines up with the diode). The pins are closely spaced, so check very carefully between each pad after soldering for dags shorting out pads. If necessary, use a multimeter or a magnifying glass. Next the large components – the relay, trimpot and electrolytic capacitor – can be soldered in place, followed by the piezo buzzer. As the photograph shows, this is mounted edge-on to the PC board with the pins connected to vertical wires soldered to the appropriate PC pads. After checking thoroughly, carefully insert the BASIC Stamp module into the 14-way socket. Take care that all pins actually go into the socket and mate properly – it’s easy to bend them. It’s also easy to insert the module backto-front: make sure the components on the module face the input socket. STAMP EXPERIMENTER'S BOARD Figs.2 & 3: the circuit (above) and PC board layout (below) for BASIC Stamp experiments and circuit development. With the components shown either the simple or complex timer can be built but the large number of spare pads make adapting this exclusive SILICON CHIP design very easy. What else do you need? Now that you’ve finished the BASIC Stamp PC board you’re just itching to get going, right? Whoa! It’s simple, but not quite THAT simple. There are a few more things you'll need. First and foremost, you need software that will allow your PC to communicate with (and program) the BASIC Stamp. For BASIC Stamp 1 (which we are using) the software is stamp1.exe. You’ll also need connecting cables and, unless you’re already a wizz at PBASIC and programming, some form of driving instructions. Fortunately, there’s an easy way to get all this in one package. Dick Smith Electronics stores stock the BASIC Stamp Development kit which contains all of the above for less than $150. It also includes a certificate entitling you to three months free technical support. The BASIC Stamp manual, by the way, is more than 460 pages thick so it’s no lightweight. It contains 23 application notes to try out and also contains information on the higher spec’d BASIC Stamp II. Fig.4 (below): use this PC board layout to make your own board or to check commercial boards. The pattern is also available for download (in Adobe PDF format) from the SILICON CHIP website: www.siliconchip.com.au January 1999  35 Both these books from Dick Smith Electronics will be invaluable for anyone interested in the BASIC Stamp. A Few Stamp FAQs Before we conclude our look at the BASIC Stamp, we’ll try to answer a few FAQs (for those not into webspeak, that stands for frequently asked questions). ‘‘Programming and Customizing the BASIC Stamp Controller’’ (left, $77.95) has nearly 300 pages with many BASIC Stamp projects to try. It also includes a CD-ROM with a variety of software tools and the BASIC Stamp applications, along with the stamp1.exe software. “Can the program storage memory be increased?” No, the PBASIC interpreter only addresses 8 bits of program space, which results in the 256-byte limitation. Using a larger EEPROM won’t make any difference. It is possible to use external memory for storing lookup tables and extra data – you’ll find information on this in the BASIC Stamp manual. “Can the BASIC Stamp support floating point maths?” No, it only works with integer maths, which means fractions are out. If your program required the BASIC Stamp to divide 7 by 2, it would give you the answer 3, not 3.5. “Speaking of maths, how does the BASIC Stamp evaluate maths expressions?” Strictly left to right – not, as you might expect, following maths conventions. For example, a BASIC Stamp would evaluate 1+2x3 as 9, not 7. That is, it would work it out as (1+2)x3, not 1+(2x3). “What is the BASIC Stamp’s life?” Hard to say! A program is guaranteed to stay in memory for 40 years but there is a finite limit to the number of times the EEPROM can be reprogrammed. Fortunately, that limit is about 10 million times so you’re hardly likely to reach that in a hurry. However, swapping files to and from the EEPROM (in an effort to overcome the 256-byte limitation) could reach this limit much more quickly, so this is not recommended. “How do I get more than 25mA output current from the I/O lines?” You don’t – that’s one of the quickest ways to blow up the processor. That is precisely the reason we added the ULN2003 buffer: it can sink up to 350mA collector current per output (not 500mA as you might see claimed). If you drive all seven ULN2003 inputs gates from the BASIC Stamp I/O you'll still be under the 40mA maximum output limit. 36  Silicon Chip The ‘‘BASIC Stamp Manual’’ (below) is part of the BASIC Stamp Development Kit ($149) which also includes the cables and software. If you already have a working knowledge of the BASIC Stamp and don’t want to buy the Development Kit, an alternative would be to buy the programming cable (also available from Dick Smith Electronics – Cat K-1407 <at> $19.95). Another very handy reference is the Scott Edwards book, “Programming and Customizing the BASIC Stamp Computer” (you guessed where from – Cat B-4807 <at> $77.95). It contains a host of very detailed information, projects and even a CD-ROM of software tools including the stamp1. exe program. Meanwhile, back at the ranch ... Let’s assume you have the BASIC Stamp board completed, the programming cable to connect to your PC and copies of the experimental software. Ah! Experimental software – we haven’t mentioned that yet, have we? The experimental BASIC programs (as distinct from the executable stamp1.exe) are all listed overleaf. Simply type them as a text file in any word processor or text editor and save them with the names shown. But if you don't feel like doing all that typing, don't! All listings are available from the “Software Downloads” page on the SILICON CHIP website – www.siliconchip.com.au – and the best part of all is they are free! So before we get too much further down the track type out the software or log on to the website and download it. There are four programs – adjust. bas, test.bas, simple.bas and complex. bas. All four files come to less than 6kB so they’ll only take a few moments to download. That is, unless you want to explore the SILICON CHIP website while you’re there! OK, so we’re ready to go. The first step is obvious: connect the programming cable to the BASIC Stamp and to your PC’s parallel port. About now you’ll be starting to think "Perhaps I should have put the paint spots on those cables. Which way around do they go?" Plug in power and turn on the computer (the IBM compatible, that is). We mentioned a moment ago that the software is tiny. Even stamp1.exe is only 14kB. Therefore it is perfectly practical to run the BASIC Stamp software from a floppy-disc-only computer. Yes, we really did mean any IBM compatible! If you have a hard disc, of course, it’s preferable to run it from that, if only because you’ll never misplace the floppy disc. Create a directory called STAMP1 and copy stamp1.exe and the four BASIC programs into it. It makes sense to include the STAMP1 directory in your DOS “path” statement, especially if you’re going to be doing a lot of experimenting with files. Which ever you choose, floppy or hard disc directory, go to your DOS prompt and log on to that disc or directory. Load the operating software for the BASIC Stamp 1 module, stamp1.exe. Once stamp1.exe is loaded, you should have an almost blank, blue screen as shown overleaf. Fear not! You haven’t loaded one of Mr Gates’s blue screens of death. Your next step is to load the experimental BASIC programs which you downloaded. Just a reminder – these are just ideas to get your creative juices flowing. Once you’ve played with the BASIC Stamp, you could come up with a whole host of ideas! Where to get help The BASIC Stamp project described here and the accompanying software is, of necessity, very elementary – just enough to whet your appetite to develop bigger and better applications using this simple, yet clever little module. Because of its simplicity, we imagine that very few constructors will have any difficulties with this project as published but that may not be the case as you expand your horizons. So where do you go when you need help? If you buy the Dick Smith Electronics development kit, you will receive a certificate entitling you to three months software support through the Australian distributors, MicroZed Computers. This is available by phone (02) 6772 2777; fax (02) 6772 8987 or email – support<at>microzed.com. au Note that support is available for STAMP product and software obtained only through Dick Smith Electronics or MicroZed. You can also obtain information and support through the Microzed web site, www.microzed.com.au A great deal more information and backup support is available from the Parallax website, www.parallaxinc. com There’s even an evaluation copy of stamp1.exe to help you decide if you want to buy the real thing. As mentioned before, if you don't feel like typing them out the four PBASIC programs – adjust.bas, test. bas, simple.bas, and complex.bas – are all available from www.siliconchip. com.au; however technical support is not available from this website nor SC from SILICON CHIP magazine. * Bob Nicol manages MicroZed Computers, authorised Australian distributors of Parallax Inc's products. OVERLEAF: HOW TO LOAD THE SOFTWARE PLUS COMPLETE PBASIC LISTINGS January 1999  37 LOADING THE SOFTWARE Loading BASIC Stamp software is a three-part process: first load the application software (stamp1.exe) into your IBM-compatible PC; second load the PBASIC program (*.bas) from disc into your PC; third download it to the BASIC Stamp module. Load stamp1. exe from the DOS prompt (it doesn’t matter whether you do it from DOS itself or from a DOS Window. Our screen shots show the latter). A nearly blank blue screen should appear as above. Type ALT L (ie, hold down the Alt key and touch the L key at the same time). This will bring up a menu of the *.bas software in your STAMP1 directory. In this case we are choosing adjust.bas. Type ALT R to run.The program takes about a second (or less) to download to the BASIC Stamp and if all is OK, will run immediately. The histogram which appears shows how much BASIC Stamp memory is taken from total memory, the red or dark portion showing memory used. Once loaded, it stays until another is loaded. If there are ‘‘debug’’ lines in your PBASIC program they will show up on the first loading. 38  Silicon ilicon C Chip hip 38  S Setting the LDR – adjust.bas ’adjust.bas - LDR threshold setting - Silicon Chip January 1999 ’This short program allows setting of the LDR to an appropriate level ’LED is on pin 6 via ULN2003 Solenoid driver chip ’LDR is on pin 5, adjust the potentiometer, when LDR is in light ’then hold finger over LDR adjust so that LED goes off LOOP: LOW 6 IF PIN5 = 1 THEN LED GOTO LOOP ‘this segment looks at LDR ‘turn LED off ‘Goto subroutine named LED ‘go back to beginning, to look again LED: HIGH 6 ‘this segment turns LED on ‘this line does just that GOTO LOOP ‘go back to look at LDR again First of all, load the “adjust.bas” program. This lets you set the threshold of the LDR between light and dark. Now you can adjust the trimpot. If the LED is on, turn the pot anticlockwise to the point where it just turns off, then back again until it just turns on. Put your finger over the LDR and the LED should turn off. Note that this setting applies to the light levels in that room at that point – if you change locations you might need to run adjust.bas again. One point to keep in mind: the BASIC program loaded into EEPROM is going to stay there for a long, long time – it’s guaranteed for 40 years, even with power removed. It will also keep operating even if the PC which programmed it is turned off and/or disconnected. You can erase the contents of the EEPROM by loading another program – which is exactly what we are going to do now. The simple timer – simple.bas ’Simple.bas - Simple Timer - Silicon Chip January 1999 LDR: ’this segment looks at LDR LOW 0 ’turn relay off LOW 6 IF PIN5 = 0 THEN RELAY ’Goto subroutine named RELAY GOTO LDR ’go back to beginning, to look again RELAY: ’this segment turns relay on HIGH 0 ’this line does the job ’ HIGH 6 ’this line turns LED on too, to enable ’line remove first apostrophe in line PAUSE 20000 ’Stamp marks time for 20 seconds GOTO LDR ’go back to look at LDR again The simple timer is an example of a BASIC Stamp application which may or may not be particularly useful – but it’s an interesting example nevertheless. Do you have a deep cupboard or storeroom which doesn’t have a light of its own, or where the light can’t reach into the furthest corners? This BASIC Stamp program might solve that problem. It is designed to sit in a cupboard or room and sense when the cupboard or storeroom door is opened, allowing some light in. The LDR in the circuit senses the light and the microprocessor pulls in a relay (via the interface chip). This can then be used to turn on an additional light (battery operated?) in that dark corner. Overkill, when you can do the same thing with an LDR and transistor? Probably. But these applications are not intended to be so much practical as examples of what can be done with the BASIC Stamp. You will have noticed that no details are given for the connection to the light – that’s the easy part! Once again, follow the “adjust.bas” steps to load the software. Note that the additional light must not be in the field of view of the LDR, otherwise the system becomes a closed loop and the additional light will be locked on all the time. With the software as it stands, the light will stay on for 15 minutes. The BASIC Stamp test – test.bas ’Test.bas - test components on timer PCB - Silicon Chip January 1999 SOUND 7,(100,1000) ‘beep piezo sounder for 1 second HIGH 0 ‘relay on HIGH 6 ‘LED on TEST_LOOP: DEBUG “pin 5 getting logic “, #PIN5, “ from LDR”,CR IF PIN5 = 0 THEN ALL_OFF ‘turn everything off IF PIN5 = 1 THEN ALL_ON ‘turn everything on GOTO TEST_LOOP ‘tedious, but let’s do it again ALL_OFF: ‘this section of the program turns all devices off & beeps LOW 6 ‘LED off LOW 0 ‘relay off SOUND 7,(100,10) ‘one beep each time around GOTO TEST_LOOP ‘back to the tedious bit ALL_ON: DEBUG “ * * * * * * “, CR ‘separates DEBUG lines on screen HIGH 6 ‘LED on HIGH 0 ‘relay on SOUND 7,(120,5,120,5) ‘two short beeps each time around GOTO TEST_LOOP ‘back to the tedious bit This little routine puts all of the on-board components through their paces just to make sure everything is working properly. Apart from that, it doesn’t do very much except demonstrate how the program interacts with the hardware! Loading the program is exactly the same as loading the adjust. bas above, with the obvious exception of the program name! What this will do is sound the piezo buzzer for 2 seconds, light the LED, close the relay and pulse the piezo buzzer. It will stay in that state until you block the light to the LDR, when the LED goes out, the relay drops out and the buzzer tone drops and quickens. The complex timer – complex.bas (listing at right) Aunty Maud has left you with her much loved but rather delicate pot plant with strict instructions to water it every evening. Alas, you’ve forgotten it for the last three days and the pot plant is looking, well, not well. Wouldn’t it be nice if you had another brain to do it for you? BASIC Stamp has a brain! With the complex timer software loaded it will sense dusk, turn on the relay for a minute (or whatever other time you set from about 1/1000 of a second (!) right up to a minute – or more correctly, 65,535 milliseconds). That’s as the program is written – but if you wanted to, you could add extra “pause” statements and eventually drown the poor plant, the dog and the next door neighbour’s oak tree. The timer doesn’t trigger again until the next dusk. The program takes into account that night time is just a bit longer than the normal watering cycle of the system. And if you’re really clever in setting the LDR threshold and writing code, it could even detect full cloud cover and skip those days. It also takes into account daylight but will ignore a torch or car headlights flashed on it. It really does have a lot of features but there are many more which could be incorporated – it just depends on how clever you want to be at adapting the complex.bas program. Exactly how you water Aunty Maud’s pot plant is left up to you – there’s a relay output to turn on your ingenuity, we’re sure (or is that a mixed metaphor?). A windscreen washer pump or a valve connected to an overhead bucket are both ideas that spring to mind. But the purpose of this software is not so much to demonstrate what to do but how it can be done and modified to suit your requirements. Now, who's into hydroponics . . . These program listings are also available for downloading free of charge at the SILICON CHIP website: www.siliconchip.com.au COMPLEX.BAS - COMPLEX TIMER LISTING ’Program for Complex Timer - Silicon Chip January 1999 ’by Bob Nicol, MicroZed Computers ’DEBUG statements are used in this program. They show on your PC screen the first time 'you load the program and NOT when program is run again. ’DEBUG statements should be disabled with an apostrophe, and the program loaded to the 'Stamp again when you have finished editing and checking the program to suit your needs ’pin assignments and settings, plus some startup fiddles: ’PIN 0 output to pin 7 of ULN2003 to drive relay on pin 10 LOW 0 ’Make sure pin 0 is low LOW 1 ’PIN 1 Not used set low LOW 2 ’PIN 2 Not used set low LOW 3 ’PIN 3 Not used set low LOW 4 ’PIN 4 Not used set low INPUT 5 ’sets pin 5 as an input to accept LDR level ’PIN 6 output to pin 4 of ULN2003 to drive LED on pin 11 of ULN HIGH 6 ’turn LED on PAUSE 1000 ’leave LED on for 1 second LOW 6 ’Then turn LED off and make sure pin 6 is low ’PIN 7 output to piezo sounder SOUND 7,(100,200) ’make a noise on start up ’Variables ’B2 accumulates number of times LDR (PIN 5) is low ’B3 accumulates number of times LDR (PIN 5) is high ’B4 accumulates count for reset B2 ’W4 accumulates darkness events ’B5 Flags ACTION already done WAITING_FOR_CHANGE: ’This program module keeps looking at LDR ’and initiates action when LDR is dark ’long enough to be a valid condition DEBUG “PIN 5 IS “,#PIN5,CR ’shows if LDR on pin 5 is in dark(0) or light(1) DEBUG “LDR HAS SEEN DARK “,#B2,” TIMES”,CR ’shows on PC screen DARK / LIGHT DEBUG “LDR HAS SEEN LIGHT “,#B3,” TIMES”,CR ’counts in B2(DARK) & B3(LIGHT) PAUSE 1000 ’wait one second IF PIN5 = 0 THEN INCREMENT_D ’goto increment_D to add 1 to B2 IF PIN5 = 1 THEN INCREMENT_L ’goto increment_L to 1 to B3 B4 = B4 + 1 ’add 1 to B4 DEBUG “LDR has been looked at “,#B4,” times”,CR,CR PAUSE 1000 ’wait one second IF B4 > 5 THEN DECREMENT ’B2 hasn’t increased, go to DECREMENT ’to reset B2, B3 & B4 GOTO WAITING_FOR_CHANGE ’keep going around this loop INCREMENT_D: ’LDR has seen darkness DEBUG “INCREMENT DARK B2 “,CR,CR ‘PC screen shows we are in increment B2 = B2 +1 ’B2 gets one more added to it IF B5 = 1 THEN HOLDOFF ’intercept Action, already done IF B2 > 10 THEN ACTION ’LDR has seen at least 10 Dark signals GOTO WAITING_FOR_CHANGE INCREMENT_L: DEBUG “INCREMENT LIGHT B3”,CR,CR B3 = B3 +1 IF B3 > 10 THEN RESET_B5 GOTO DECREMENT DECREMENT: DEBUG “DECREMENT”,CR DEBUG “RESETING LDR STATUS”,CR,CR B2 = 0 B4 = 0 GOTO WAITING_FOR_CHANGE ACTION: SOUND 7,(60,100,80,100,100,100,120,100) DEBUG “ACTION, RELAY ON, LED ON”,CR,CR HIGH 0 HIGH 6 PAUSE 2000 LOW 0 LOW 6 B2 = 0 W4 = W4+1 B5 = 1 DEBUG “Darkness has occured “,#W4,” times”,CR GOTO WAITING_FOR_CHANGE HOLDOFF: DEBUG “ HOLD OFF UNTIL LIGHT SEEN” B2 = 0 GOTO WAITING_FOR_CHANGE RESET_B5: DEBUG CR,CR,” R E S E T B5 & B3",CR,CR B5 = 0 B3 = 0 GOTO WAITING_FOR_CHANGE ’get back to looking at LDR signal ’LDR has seen light ’B3 gets one more added to it ’seen enough light to make change ’reset dark and light variables ’there has been no valid darkness ’show on PC screen decrease happened ’set darkness count to zero ’set false counts to zero ’go back to looking at LDR signal ’Darkness criteria met, do something about it ’audible warning of action ’show on PC screen we are doing it ’turn relay on via ULN2003 ’turn LED on via ULN2003 ’stay that way for 2 seconds ’turn relay off ’turn LED off ’reset B2 ’keep count of times turned on ’show on PC screen count of events ’go back to looking at LDR signal ’this is a loop to stop action already taken ’show on PC screen ’reset B2 ’go back to keep looking at LDR ’Stop HOLDOFF cycling ’Show on PC screen ’when B5 is 1 HOLDOFF is used ’reset light counts ’go back and keep looking at LDR ANUARY 1999  39 1999  39 January