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The Simplest Digital Alarm Clock Ever PIC-TOC PIC-TOC What has less than twenty components and can make sure you wake up in time for work, school, that early morning golf game . . . It’s an alarm clock, of course. But it’s not just any alarm clock . . . It’s a PIC TOC! Design by Michael Moore ­Words by Ross Tester N ow before you say “Oh no, not another clock project…” have a closer look at this one. It has just a handful of components yet offers features such as a melody alarm, high-brightness readout and a seconds display. It’s designed to operate from a plugpack supply but is just as happy running from a car or caravan battery (in fact, anything from about 9-17V DC). So if you’re travelling a lot and want a reliable alarm clock for the ’van or motorhome, this one is ideal. And you’ll be able to knock it up in less than an hour. Everything mounts on one small PC board and the “case”, if you can call it that, is simply a cheap, tiny photo frame from your local bargain store (about two bucks’ worth!). And because it’s based on a PIC micro, we’ve called it the PIC TOC. Oh, come on, it’s not that bad! PIC TOC. TIC TOC. Geddit? The circuit As you might expect, to be as simple as what it is the clock uses just a single micro – in this case, the ubiquitous 60  Silicon Chip PIC16F84. All that is attached to the PIC is a 4MHz crystal-controlled oscillator (so it’s nice and accurate), the push-button setting switches, a buzzer and four low current, high intensity 7-segment LED displays (via suitable resistors). Apart from the power supply, that’s all there is to the circuit. The secret is, of course, in the software – FEATURES: build!  Cheap and easy to  4 very bright digits  Push-button setting  Melody alarm  AM/PM indication in this case, the PIC is loaded with a program called alexcloc.hex. And just in case you’re wondering, Alex is the little girl this clock was first built for. So now you know! PortA 0-3 (RA0-RA3) of the PIC serves as the multiplexer, sourcing one of four seven-segment common anode LEDs in turn. These LEDs re- quire just 3mA per segment and give a nice bright display straight from the PIC without the added complexity of driver or multiplexer circuitry. 3mA times 8 segments (don’t forget the decimal points!) equals 24mA – just below the 30mA sourcing limit of a PIC16F84 I/O port. The fifth PortA (RA4) is used to drive the audio output, which goes to a piezo buzzer. RA4 is an “open drain” output – that is, it will only go low, not high. Because of this, some buzzers may require a resistor in parallel (say 1.1kΩ to keep it all nice and simple!) but in the case of the buzzer specified, no resistor is necessary. Provision is made for such a resistor on the PC board should it be needed. PortB feeds the individual LED segments – when one of the PortB I/O pins (RB0-RB7) goes low, the segment turns on. Obviously, Port A controls on which digit the segment gets turned on. PortA multiplexer outputs which are not having a turn as a source are kept in the high impedance input mode. This is more for experimental reasons than anything to do with the The PICTOC is housed in one of the cheapest cases we’ve ever used: a $2.00 photoframe! But it sure looks the part . . . design/software presented. By putting them into high impedance mode, it would be possible to add on additional common cathode 7-segment LEDs in parallel with the existing four common anode 7-segment LEDs, or add a set of switches. Port A can act as a Tristate 4-output pin multiplexer, giving each of 4 pins a turn at being a sink, a source, or off. Incidentally, I had planned originally to add two extra 7-segment displays to the clock (ie, seconds) but decided not to do so because the extra LEDs would have reduced the brightness. There is nothing to stop this circuit being adopted to become a frequency counter, tachometer or variable sweep generator with appropriate software – and in this case, brightness is probably less important. Four switches are connected to the highest digit’s PortA pin (RA0). Every hundred milliseconds or so, PortB (which normally drives the LED segments) is switched to input mode and RA0 goes low. If one of the switches is being pressed the relevant PortB input will be pulled low. The software detects which switch is being pressed. Normally, these switches would short out the corresponding LED segment when pressed unless they were connected via a diode opposite in polarity to the LED segment. But in this case – a 12-hour clock – only three segments are used for the highest digit’s display. So the four switches are connected to the unused segments, keeping the component count to a minimum. The program We are not going to attempt to print the program listing for alexcloc.hex – Here’s another view of the photo-frame “case”, this time sans bits. You cannot even see the glass – but it’s there. We would have preferred a piece of red acrylic but didn’t have any on hand. . . apart from taking a lot of pages, who in their right mind would type it out when you can download it, free of charge, from the SILICON CHIP website: www.siliconchip.com.au? This program can be loaded into your PIC using one of the PIC Programmers described earlier this year (January and March 2001 issues). Alternately, it is expected that some kit suppliers will have available pre-programmed PICs. There is only one hardware timer in the PIC16F84, and this is needed to keep a precise count for the clock. So it cannot be used to produce audio output – a software timer is used to regulate the audio tone instead. All the main duties such as monitoring the hardware timer, keeping track of the time, multiplexing the digits and so on, are broken down into identical length subroutines. The main program counts these subroutines to time the period of the note that is being played and can therefore generate a note at the correct frequency. The main program actually generates a tone continuously but the tone is inaudible unless a key is pressed July 2001  61 or the alarm goes off . The method is not exact but is exact enough – the ear cannot detect anything amiss! Construction The clock is housed in a tiny picture frame. OK, so it’s not quite in – it’s more ON the picture frame, surrounded by part of a plastic box. All components – switches included – mount on a small PC board, coded 04207011. Most components mount in the normal way on the top of the board. The exceptions are the four time-setting switches, the main filter capacitor and the piezo buzzer, all of which solder to the back (copper side) of the board. Start by cutting and soldering the various links on the PC board. Some of these are very close together and should therefore be insulated. Also, room must be left for the 7-segment displays – some links are hard against the displays. One link, on the right side, actually goes around the end display so ensure enough length is left to achieve this. Next, solder in the four LED displays. Note that two of these mount the opposite way to the other two (this gets the “colon” between the hours and minutes. Note where the labels on the displays are and place them the same way as shown on the component overlay (Fig. 2). Be careful soldering the pins – there isn’t a great deal of room between them (the same comments apply to the PIC Fig.1: yes, this is the complete clock circuit. There’s not much in it, is there! Just a PIC, oscillator, piezo buzzer and four setting switches plus power supply regulator make up the entire project. 62  Silicon Chip Here’s the DSE Utility Case after we “operated” on it to make it shorter than the maker intended! At 10mm high and with no “bottom”, it’s perfect for the switches to poke through as seen in a later photograph. The “stand” came from the original frame. Fig.2: here’s how the components go on the PC board. The four push buttons, 100µF electrolytic capacitor and piezo buzzer are mounted on the underside. socket and the resistor array. Make sure the PIC socket goes in the right way around (cutout closest to the edge of the board). If your eyes aren’t as good as they once were (and perhaps even if they still are!) check for solder bridges with a powerful magnifying glass. The PC board is designed for either an 8 x 1.1kΩ resistor array or eight individual 1.1kΩ resistors. We prefer the individual resistor approach because arrays are not only harder to find, they’re more expensive. Complete the top side construction by soldering in the polarity protection diode, regulator, crystal and various capacitors. Crystals and ceramic capacitors aren’t polarized; electrolytic capacitors are. Note that the 10µF capacitor lays on its side. Now turn the board over for soldering on the underside components. Three of the switches – black, green and yellow – mount the same way with their flat side facing to the left when you look at the copper side of the board with the switches at the bottom. The fourth switch, the red one, mounts with its flat side facing upwards – see the component overlay again for a clearer picture. You’re going to need a very fine point on your soldering iron to solder the switch pins to the tracks underneath. The 100µF electrolytic capacitor and piezo buzzer solder on the underside of the PC board. The capacitor (lying on its side) is easy because you have access to the legs. The buzzer is not so easy. The way we did it was to apply solder to the copper pads, poke the There are minor differences between this photo and the overlay at left (it’s of an earlier prototype) but nevertheless will give you a good idea of where the bits go! piezo’s leads through and then heat the leads from the top side. This melted the solder underneath and the joint was made. But it’s not a method you’ll find in the rules according to Hoyle (or whoever wrote the soldering rules!). Remember too that the piezo is polarised – it won’t work the wrong way around. Finally, solder in the wires to the DC supply socket. The socket should be connected with the positive to the center, which is the convention for plugpacks more often than not – until some idiot manufacturer decides his plugpacks are going to have negative to the middle! There’s not much room in the case to mount the DC socket – we managed to squeeze it in one side after making sure all the terminals were well covered with insulation to prvent shorting to the back of the PC board. The protection diode will prevent any catastrophes if you do use a wrong-polarity plugpack – but of course, the clock won’t work. You’ll need to find a plugpack with the right polarity – anything capable of seven or more volts (up to about 17V) and a couple of hundred milliamps will be fine. Carefully plug the pre-programmed PIC into its socket – the right way around and without bending any pins – and your clock is now electrically complete, ready for testing and then mounting in its case. Testing Apply power via the DC socket. The display should read 1:23, with a dot up in the left corner (indicating PM). And you should be greeted with a “ta-da” tone. Press the black (mode) button – it cycles the display through its various modes. Press once and the display changes from hours/minutes to seconds (preceded by a high-pitched tone), press it again it changes from seconds to alarm (preceded by a short melody) and press it one more time to switch The purpose of this pic is two-fold: (a) to show the way we (carefully!!) soldered the four pushbutton switches to the back of the PC board (with the piezo buzzer and electrolytic capacitor somewhat hidden behind) and (b) to highlight the fact that two of the 7-segment displays are reversed with respect to their mates. July 2001  63 At left is the reverse (copper) side of the PC board (again, an earlier prototype than the final board whose same-size pattern is shown above). As you can see, this board also needed a bit of surgery due to over-etched tracks – something you need to check your board for. back to clock mode again (preceded by a low-pitched tone). If all this is OK, move on to checking the alarm function with the red button. Pressing this not only turns the alarm on (and of course off), it also lights the bottom right dot LED to show it is in alarm mode. Finally, the green and yellow buttons are used to change the two left and two right digits respectively, incrementing the digits in both clock Parts List – PIC TOC 1 PC board, 50 x 75mm, coded 04207011 1 Plastic utility case, 57 x 82 x 33mm (DSE Cat H-2923) 1 Miniature wooden photo frame (with glass), 107 x 81 x 17mm with   “photo” cutout 51 x 76 x 10mm (available from bargain stores) 1 2.5mm DC power socket 1 mini PC board mounting normally open single-pole pushbutton  switch, red (Jaycar SP-0720 or similar) 1 mini PC board mounting normally open single-pole pushbutton  switch, yellow (Jaycar SP-0722 or similar) 1 mini PC board mounting normally open single-pole pushbutton  switch, green (Jaycar SP-0724 or similar) 1 mini PC board mounting normally open single-pole pushbutton  switch, black (Jaycar SP-0721 or similar) 1 piezo transducer, PC board mounting (Jaycar AB-3459 or similar) 1 4MHz crystal 1 200mm length of insulated tinned copper wire (for links) 1 100mm length mini figure-8 (or two strands of rainbow cable) Semiconductors 4 HDSPH101 high intensity, low current, 7-segment common anode  LED displays (Farnell Electronics 324-723) 1 PIC16F84, pre-programmed with alexcloc.asm (downloadable from www.siliconchip.com.au) 1 78L05 low power 5V regulator (TO-92 package) 1 1N4004 silicon power diode Capacitors 1 100µF 25VW PCB-mounting electrolytic 1 10µF 16VW PCB-mounting electrolytic 1 0.1µF ceramic or polyester (code 104 or 100n) 2 22pF ceramic (code 22 or 22p) Resistors (0.25W, 1%) 8 1.1kΩ (brown brown red brown or brown brown black brown brown) * * PC board will also accept an 8 x 1.1kΩ resistor array 64  Silicon Chip and alarm modes. In seconds mode the yellow button increments the minutes and the green button resets the seconds to zero. If all this appears to be working as it should, you only have two more tests to make. One is that the clock does actually work – set the time and ensure the digits change – and the other is that the alarm actually works – set the alarm time for, say, two minutes ahead and then wait that two minutes to ensure that Beethoven’s Pastoral Symphony greets you! Once you’re happy it all checks out OK, it’s time to place the clock in its unique case. The “case” As we mentioned before, the clock mounts inside a cheap (two dollar) miniature photo-frame which we obtained from our local bargain store. The frame we used measures 107 x 81mm and is about 17mm deep but the more important dimension is the cut-out for the “picture”. In our frame it was 76 x 51mm – you’d almost think the PC board at 75 x 50mm was designed to fit, wouldn’t you? Our frame had a small piece of glass, against which you’d normally place the picture. Instead, we placed the PC board – the LEDs contacting the glass. To be honest, we would have preferred a piece of 2mm-thick red acrylic in place of the glass – it would hide everything inside and accentuate the LEDs. But time beat us so we stuck with the glass. Now, what holds the PC board in place? You can’t use the normal backing supplied but don’t throw it out – we’re going to use the support stand attached to it. Instead, we used a Utility Box from Dick Smith Electronics. Actually, that’s a lie: we used 1/3 of a Utility Box from Dick Smith Electronics. The box we used (H-2923) has cable entries and mounting points emerging from each end. We didn’t need the cable entries but the mounting points we did! The box is 57 wide, 82 deep and 33mm high. The width and depth are fine, the height is far too much. So we removed the lid and carefully measured a line 12mm down from the case top, cut this with a hacksaw then smoothed it on a sheet of sandpaper (ie, rubbing it on the sandpaper, not the other way around). The photo shows you what we ended up with. In the lid, we drilled 10mm holes for each of the four pushbutton switches and the DC socket (see photo above right). And remember that support stand we mentioned a moment ago? This was also fastened to the lid to allow And it’s finally assembled. We see a cut-down instrument case which holds the “works” onto the photo-frame. The four push- buttons set time and alarm. What you cannot see in this photo is the side-mounted socket for DC power input. the clock to stand up vertically (again, refer to the photographs). The PC board is not glued or screwed to the case – it doesn’t need to be. Just pop the four push-buttons through their holes. (That’s the reason the holes are slightly oversize – it allows for a little bit of error.) When finished, we simply placed the lid onto our piece of case and screwed the whole lot to the wooden frame Winning Gold . . . . . .After the Games EX OLYMPIC GENUINE MAG LITE TORCHES Made in USA, complete with 240V battery charger kit and in car battery charger kit. As used by Police, Navy & RTA using some 20mm self-tappers. (Drill a pilot hole in the frame first to avoid splitting). If necessary, some foam rubber can be slipped in between the lid and the PC board to keep the LEDs hard against the glass in front. And that’s it. Plug in power, set the clock and settle back and enjoy! Now, what can we do with 2/3 of a SC utility case without a lid? HURRY! This is your LAST CHANCE to grab some of the equipment left over from the Sydney 2000 Olympic Games at never-to-be-repeated prices! CALL NOW! 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