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How many times have you opened up that favourite board game to find that someone has pinched the dice? In that case, why not build this electronic die which uses just two CMOS ICs? It simulates the roll of a real die and even turns itself off. Build this elegant electronic die By DARREN YATES Die or dice - which is correct'? Let's straighten that question out right at the start. "Die" is the singular form of 'dice" so it is correct to term a unit which will randomly indicate 1 to 6 as a die. There have been a number of designs over the years for simulating a 6-sided die but most either use a 7-segment display to show up the numbers 1 to 6, or a row of 6 LEDs to indicate the die number rolled. But although these circuits are simple, they don't give a realistic display. When you roll a 6-sided die, it rolls along with the initial momentum of the throw, and then slows down until it stops. How many times have you almost seen a "6" turn up on the die, only to see it turn over into a lousy "1 " '?. This circuit cycles through the numbers 1 to 6, and slows down until it stops on its final number. This is far more realistic than pressing a 34 SILICON CHIP button and having the final number instantly staring you in the face. Another feature of a real die is the dots on the faces. This has often been a tricky task to achieve electronically, and most circuits don't bother about it. Our circuit has this built in, with all the displays matching the faces of a real die, including the diagonal "2" and "3". Fig.1 shows how all numbers are displayed. Another problem with electronic die circuits we have seen in the past is that it is all too easy to leave them switched on so that they flatten the battery. This design has no on/off switch - it turns itself off automatically, after 50 seconds. The circuit Now let's have a look at the circuit diagram - see Fig.2. It uses only two low-cost CMOS ICs, seven light emitting diodes (LEDs) and not much else. ICl is a 4015 dual 4-bit .. ,.. Fig.1: here's how all the numbers are displayed by the LEDs. Note that the displays match the faces of a real die, including the diagonal "2" and "3". +6V 100 + 16VWJ ROLL S1 I C2 33 10VW + 70 ~ 1 C ,o.::.-4,___ _;:1---."fg C 4~c,1s"e R~6_ _ 15 D 16 R3 f-...,1Y,Ok~+----'14 R IC1 ! 02 11 00 .,. 00 LED1 LE07 R2 LE03 180k LE01Q LE02Q LED3Q QLED5 LED4 Q QLE06 QLED7 CMOS LED DIE Fig.2: when the ROLL button is pressed, Cl & C2 discharge and oscillator IC2a clocks 4-bit shift register ICla. ICla in turn clocks IClb and their outputs drive the display LEDs. As C2 charges, IC2a slows and eventually stops to give a static display. The LEDs then turn off after 50s. register while IC2 is quad NAND Schmitt trigger. The circuit works as follows . If you press the ROLL button Sl, capacitor C2 is shorted out while Cl is shorted via diode D2. Once the ROLL button is released, capacitors Cl and C2 begin to charge again and while they are doing so, the rest of the circuit can function. Also, when the ROLL button is pressed, capacitor C4 quickly charges via the 560kn resistor R4. These two components are part of an oscillator associated with Schmitt trigger NAND gate IC2a. C4 is charged via R4 as just noted but once the capacitor voltage reaches the positive threshold of IC2a, its output flicks negative and then C4 is discharged via diode Dl and the series lOkQ resistor. This happens repeatedly and results in a series of short negative going pulses (at pin 3 of IC2) which decrease in frequency until they stop altogether after about 5 seconds. This 5-second time period is set by the charging of capacitor C2 and the negative threshold of IC2a. The pulses from IC2a clock the circuit and simulate the roll of a real die, whereby the LEDs cycle very rapidly at first and then slow to a complete stop to give one of the static displays shown in Fig.1. The clock pulses are fed to pin 9 of ICla, a 4-bit shift register which is connected as a D-type flipflop. ICla is made to function as a flipflop by connecting its Q0 output at pin 5 to the D input at pin 7 via inverter IC2b. The Q0 output of ICla is also used to drive LED 4 which is on for all the odd-numbered displays; ie, 1, 3, and 5. The output of IC2b is also used to clock the second 4-bit shift register, ICl b. The D input of IC1 b is tied to the positive rail so that on each clock pulse, a "high" is shifted to each output from Qo to Ql to Q2 (pins 13, 12 & 11, respectively). Pin 11 drives LEDs 6 & 2, pin 12 drives LEDs 1 & 7 and pin 13 drives LEDs 5 & 3. These LEDs produce the even-numbered displays 2, 4 & 6. When Q0 of ICl b goes high, LEDs 5 & 3 come on to produce the displays 2 & 3. On the next clock pulse, Ql now also becomes high so that the displays 4 & 5 are produced as LEDs 1 & 7 are now also lit. On the third clock pulse, Q2 goes high as well, lighting LEDs 6 & 2 to produce the displays 5 & 6. Die sequence Let's just go through the sequence whereby the circuit produces the die displays. SC08107901 Fig.3: here is a full-size reproduction of the PC artwork. JULY 1990 35 PARTS LIST 1 PC board, 105 x 57mm, code SC08107901 1 momentary contact pushbutton switch, DSE Cat. S-1201 4 1 .5V alkaline AA cells 1 4 AA-cell holder 1 9V battery snap 4 PC standoffs (plus screws and split washers) Semiconductors 1 4015 dual 4-bit shift register (IC1) 1 4093 quad NANO Schmitt trigger (IC2) 2 1 N914 silicon diodes (01 ,02) 7 red LEDs Capacitors 1 1OOµF 16VW PC electrolytic 1 47µF 25VW LL (low leakage) electrolytic (C1) 1 33µF 25VW LL electrolytic (C2) 2 .O1µF metallised polyester (C3 ,C4) Resistors (0.25W, 5%) 1 1 MO 2 10kQ 1 560k0 1 3 .3k0 1 180k0 1 1.8k0 The first clock pulse to ICla causes its pin 5 to go high and light LED 4 - the display for "1 ". The next clock pulse causes LED 4 to go out and pin 13 of IClb to go high, to light LED 5 & LED 3 - the display for "2" . The next clock pulse causes LED 4 to come on again while LEDs 5 & 3 remain alight, giving the display for "3 " . The next clock pulse causes LED 4 to go out while LEDs 5 & 3 remain on and pin 12 of ICl b goes high to light LEDs 1 & 7, giving the display for "4". With the next clock pulse, LED 4 comes on again while LEDs 5, 3, 1 & 7 remain alight to give the display for "5". Next, LED 4 goes out again and pins 11, 12 & 13 of ICl b are all high to light LEDs 5, 3, 1, 7, 6 and 2 to give the display for ''6''. The next bit is devious. In order for the die to cycle from a "6" back to a "1 ", IC2c and IC2d form an AND gate to check when Q2 of ICl b is high, indicating a 6 on the display, and when Q0 of ICla goes high again. When this occurs, the output of IC2c goes high, resetting ICl b and forcing all its outputs to go low. This now makes the output of IC2c go low again since the Q2 output of ICl b is no longer high. The resulting output of the AND gate IC2c/d is a brief positive pulse. The output of IC2c also drives the reset pin of ICla via a time constant consisting of R3 & C3. The pulse is not there long enough to cause ICla to reset while the display is cycling, allowing the display to go from a "6" back to a "1" again. If we removed R3 & C3 and then replaced R3 with a wire link, the display would cycle through 1, 2, 3, 4, 5, 6, 0, 1, 2, etc. Of course, you would have to slow down the clock pulses considerably to be able to see this sequence of events as we have described it. Auto turn off As noted previously, the circuit turns itself off automatically, to save the battery and to avoid the need for a separate on/off switch. The 47µF capacitor Cl and the lMO resistor Rl are used to provide this auto turn-off feature. As Cl charges slowly through resistor Rl, the voltage at their junction, pin 8 of gate IC2c, slowly . F ~ .01; I . e-{J]I}-e ~ rf°_rqb~'::,j__ + - 6V BATTERY Fig.4: install the parts on the PCB as shown here. Make sure that all the parts are correctly oriented and note that LED 1 faces in the opposite direction to the other LEDs. decreases. About 50 seconds after the ROLL button is released, the voltage at pin 8 reaches the lower threshold level of the gate, forcing its output at pin 10 high. Register ICl b is reset instantly and when capacitor C3 is sufficiently charged via 10k0 resistor R3, ICla is also reset, forcing all outputs low and turning off the display. The current consumption of the circuit then drops from about 3mA to approximately lµA. Construction The board is designed to sit as either a unit on its own or to fit into a small zippy box, such as DSE Cat. H-2851. All the components, including the pushbutton switch, fit onto a PC RESISTORS No □ □ □ □ □ □ 36 1 1 1 2 1 3 SILICON CHIP Value 1MO 560k0 180k0 10k0 3 .3k0 1.8k0 4-Band Code (5%) 5-111~ Coda (1'1,) brown black green gold green blue yellow gold brown grey yellow gold brown black orange gold orange orange red gold brown grey red gold brown black black yellow brown green blue black orange brown brown grey black orange brown brown black black red brown orange orange black brown brown brown grey black brown brown board which measures 105 x 5 7mm (code SC 08106901). Before you begin assembly, check that there are no shorts or breaks in any of the tracks. Fig.4 shows the wiring details of the circuit board. Start by installing the wire links and then follow with the lower profile components such as the resistors and diodes. Make sure you check the resistor values with your multimeter as you install each one. This done, the capacitors can all be installed (watch the polarity of the electrolytics ). Next, install the seven LEDs and the two CMOS ICs. Make sure they are inserted the right way around before you power up, otherwise they may be damaged. Finally, solder in the pushbutton switch (note the flat on the switch body) and the battery snap connector. If you intend to mount the die in a zippy box, we suggest that you solder in four PC stakes in the position of the switch and then solder the switch to the PC stakes to raise it off the board. This way, the board can then be screwed to the lid of the box with the switch protruding through it. Once the board has been completed, connect up the battery pack and press the button. You should see a flash of LEDs as the circuit fires into action. When you release the button, you should see the cycling rate begin to decrease until it stops on the final number. After about 50 seconds, the LEDs should go out. All that remains to be done is to pull out that favourite board game and enjoy the fruits of your labour. Troubleshooting If it doesn't work, check carefully for wiring errors. Are all the parts in the right way around? Have all the wire links been installed? Are there shorts between adjacent IC pins or PC tracks? If any of the LEDs fails to light, check that it has been correctly installed. Note that if you do install a LED the wrong way around, its series partner also won't light (eg, if LED 1 is the wrong way around, LED 7 will also remain off). Finally, don't just rush out and replace the !Cs. That seldom solves anything. ~ BOOKSHELF Music Applications of Microprocessors Musical Applications of Microprocessors, by Hal Chamberlin. 2nd edition published 1985 by Hayden Books, Indianapolis, Indiana, USA. Hard covers, 162 x 238mm, 802 pages. ISBN O 672 45768 7. Price: $59.95. While there are any number of books available on computers and microprocessors, there are precious few books on electronics in music and of those that are available, very few are of any real use. This book, by contrast, is excellent, and worth every cent of its price. Having said that , I must point out that this second edition was written in 1984 and there have been a few developments in electronic music since then. Where to start? There is so much in its 802 pages that it is difficult to know which sections to highlight in this necessarily short review. Therefore I'll start with chapter 5 which is the last of the introductory background section of this text and it is the first devoted to microprocessors. It covers microprocessor terminology and gives the early history, particularly with respect to the first personal computers such as the Commodore PET, TRS-80 and the Apple. Also covered in this chapter are peripheral devices such as printers, plotters and modems. This is very good background and worthwhile reading for anyone who was not into electronics or computing before the 80s. All told, there are 21 chapters, divided into four sections, the first of which I have already mentioned. The second of these sections, which has 6 chapters, is devoted to " Computer Controlled Analog Synthesis". Chapter 6 starts with basics such as voltage controlled oscilla tars, amplifiers and filt ers and chapter 7 goes on to treat digital-to-analog (DI A) converters. Chapter 8 is on computer control and chapter 9 on keyboard interfaces, while chapters 10 and 11 round out the section with coverage of other input devices and displays. This is very well written. The third section is entitled "Digital Synthesis and Sound Modification" and a large part is devoted to digital tone generation techniques. Fourier transforms are covered in detail, as are Fast Fourier Transforms (FFTs) and FFT Algorithms. Chapter 14, the third in this section, is devoted to digital filtering, which will be of great interest to anyone involved in digital technology, particularly as it covers reverberation simulation (as used in the Yamaha DSP-1 and similar products). Chapter 15 covers percussive sound generation, again using digital techniques, while chapter 16 is on source signal analysis, mainly spectral analysis, in 2 and 3dimensional form. Chapter 17 is on digital hardware while chapter 18 complements this with coverage of digital software. The last section of the book, with three chapters, is entitled " Product Applications and the Future " . Chapters 19 & 20 mainly cover music synthesisers while chapter 21 looks to the future . Quite frankly , as I write this continued on page 95 JULY 1990 37