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If you’re always losing the Monopoly dice, then this could save you several hours of guests climbing the walls! It uses just four CMOS ICs, has auto power-off & even imitates the dice face! Build this Dual Electronic Dice By DARREN YATES There’s no doubt about it! Whenever you go looking for your favourite board game, the odds are that the dice have been pinched for use somewhere else or are just plain missing. There are few more ugly scenes in life than a room full of guests, a Monopoly board and NO dice! So before your guests start looking for a likely piece of rope, a roof beam and a chair, you can either somehow produce two dice or pull out your newly-built piece of electronics! Not only will you save your skin but you’ll be able to wow them with your skill and expertise. This electronic dice uses just four CMOS ICs, 14 LEDs and a handful of other components. It runs from a 9V battery and au­ tomatically switches itself off 30 seconds after use. You simply press the button and the dice start “rolling”. Once you let the button go, the dice then begin to slow down and finally come to rest on one of six “faces”. Both dice are inde­pendent of each other so there’s no chance of ending up with “doubles” all night. Circuit diagram Let’s take a look at the circuit dia- The button in the middle of the circuit board controls the roll of the dice. You can mount the LEDs on the circuit board as shown here, or mount them on the lid of a case & connect them to the PC board via flying leads. 54  Silicon Chip gram – see Fig.1. The four ICs are two CMOS 4015 dual 4-bit shift registers and two CMOS 4093 quad 2-input Schmitt-triggered NAND gates. If you look carefully, you’ll see that there are two identical halves to the circuit, both controlled by pushbutton switch S1. Starting off, when the ROLL button S1 is pressed, the 33µF capacitor is shorted while the 47µF capacitor is shorted via diode D3. Once S1 is released, both capacitors begin to charge via their associated resistors to the 0V rail. However, they do so independently. Because the time constant of the 33µF capacitor and its 68kΩ resistor is less than the 47µF capacitor and its 1MΩ resistor, the voltage at the anode of diode D3 will always be lower than that on its cathode. This is important, as we’ll explain later. Pressing switch S1 also allows the .01µF capacitors con­ nected to the inputs of IC1a and IC3a to be charged via their associated 1MΩ resistors. Looking at just IC1a for the moment, these components along with the 10kΩ resistor and diode D1 make up a Schmitt trigger oscillator with a difference. As the 33µF capacitor charges, it also supplies current through the 1MΩ resistor to charge the .01µF capacitor. This happens quite rapidly and once the capacitor voltage rises above IC1a’s threshold, its output at pin 4 goes low. Diode D1 now becomes forwardbiased and discharges the capacitor through the 10kΩ resistor. Once the D1 1N914 10k 1M 5 6 .01 .01 ROLL S1 33 14 7 470 16VW 4 9 IC1a 4093 7 IC2a C 4015 R 10k 8 6 47 1k 14 LED4 IC1c 13 1k A 11 .01 .01 D3 1N914 68k 5 Q0 D LED5 12 A  LED6  LED7 K IC1b 3   K YELLOW 10 1M 9V +9V 15 16 D 13 Q0 1 12 C IC2b Q1 11 Q2 R IC1d 1 2 9 8 1.5k 1.5k 1k A LED1 YELLOW A  K LED2 YELLOW  LED3 YELLOW  K +9V D2 1N914 10k 10k 1M 1 2 .01 .01 14 7 3 9 IC3a 4093 7 IC4a C 4015 5 Q0 D 15 16 D 13 Q0 1 12 C IC4b Q1 11 Q2 R R 10k 8 6 1k 14 4 .01 .01 IC3c 5 LED12 RED 6 K 10 11 IC3b 9 1.5k 1.5k K LED13 RED   LED14 RED  K 8 1k A LED8 RED A  K LED9 RED  LED10 LED10  RED DUAL LED DICE K Fig.1: the circuit uses two identical sections. IC1a & IC1b form free running oscillators & these clock 4-bit shift registers IC2a & IC2b respectively. These then clock IC2b & IC4b (via IC1b & IC3b) to drive the LEDs (LEDs 1-7 & LEDs 8-14). capacitor voltage falls below the lower threshold of the gate, its output swings high again, forcing the diode off and allowing the capacitor to once again charge via the 1MΩ resistor. While this all happens though, A  IC3d 13 12 A 1k A LED11 LED11 RED the voltage at the negative end of the 33µF capacitor is slowly dropping as it charges up. This means that there is less current flowing through the 1MΩ resistor to charge the .01µF capacitor so that it takes longer and longer to charge up. The end result is that the short negative-going pulses from the output of IC1a take longer and longer to appear so that its frequency gradually decreases until it eventually stops altogether. This is how we generate the “slowing down” effect of the dice rolling. At this point, some of you might be May 1994  55 LED7 LED4 A K A LED1 LED2 A K A LED11 K A A A K LED3 K LED14 LED9 K S1 A K LED10 A K A K K LED8 LED6 A LED13 K A K A LED12 A K K LED5 470uF 9V BATTERY .01 1k 1k 1.5k 1k 1k 1.5k 1k 1k 10k IC2 4015 IC4 4015 .01 10k D2 1M 1M 1M 1 1 47uF 68k .01 IC1 4093 D1 10k 33uF 10k 1 D3 IC3 4093 .01 1 Fig.2 (above): try to keep the LEDs at a consistent height when installing them on the PCB. You can do this by cutting a length of 5mm-wide cardboard & then using this as an alignment tool. Fig.3 (below) shows the full-size etching pattern for the PC board. wondering why we have chosen the same components for the two oscillator sections of IC1a and IC3a. Because of component tolerances, no two components will ever have exactly the same value so both oscillators will run at a different frequency. This ensures that we don’t always get the same number appearing on both dice repeatedly. Note that this is still possible by chance, of course. From here on, we’ll just discuss that part of the circuit which involves IC1 and IC2. The other half of the circuit works in exactly the same way. The pulses from IC1a are used to clock the rest of the circuit and simulate the roll of a real dice, whereby the LEDs cycle very rapidly at first and then slow down to a complete stop to give a static display. These clock pulses are fed to pin 9 of IC2a, a 4-bit shift register which is connected up as a D-type flipflop. IC2a is made to function as a flipflop by connecting its Q0 output at pin 5 to the D-input at pin 7 via inverter IC1b. The Q0 output of IC2a is also used to drive LED 1 which is on for all odd-numbered displays; ie, “1”, “3” and “5”. The output of IC1b is also used to clock the second 4-bit shift register, IC2b. The D-input of IC2b is tied to the positive rail so that on each clock pulse, a “high” is shifted to each output from Q0 to Q1 to Q2 (pins 13, 12 & 11 respectively). Pin 11 drives LEDs 2 & 3, pin 12 drives LEDs 4 & 5 and pin 13 drives LEDs 6 & 7. These LEDs combine to produce the even-numbered displays “2”, “4” & “6”. When Q0 of IC2b goes high, LEDs 6 & 7 come on to produce displays “2” and “3”. On the next clock pulse, Q1 also goes high to produce the “4” and “5” displays, as LEDs 4 and 5 are now also lit. On the third clock pulse, Q2 goes high as well, lighting LEDs 2 and 3 to produce the “6” display. Dice sequence Let’s now follow the dice sequence. When the first clock pulse from IC1a arrives, Q0 of IC2a goes high, producing the “1” display. The next pulse pulls it low again which sends the output of IC1b high. This clocks IC2b and sends its Q0 output high, turning on LEDs 6 and 7 to produce a “2”. The following pulse toggles IC2a again, sending Q0 high and lighting LED 1 to produce a “3”. The output of IC1b is a fall­ing edge this time so nothing happens to IC2b. The next clock pulse toggles IC2a again, turning off LED 1 but clocking IC2b so that 56  Silicon Chip Q1 of IC2b also comes on to produce the “4” display. The clock pulse after that toggles IC2a again, turning on LED 1 again to produce a “5”. The next clock pulse toggles IC2a off again and clocks IC2b so that the last of the LEDs now light (via IC2b’s Q2 output) to produce a “6”. This last high also pulls one of the inputs to IC1d high and when the next clock pulse arrives, Q0 of IC2a goes high. This pulls the output of IC1d low. This low output is fed to pin 12 of IC1c. The other input to the gate is controlled by the 47µF capacitor we mentioned right back at the start. While this continues to charge up, pin 13 is held at a logic high and so IC1c acts as an inverter. The low input that has just come from IC1d thus forces the output of IC1c high, which resets IC2b. Output Q2 of IC2b now goes low again and the reset condition is removed (ie, the reset pulse is quite narrow). The RC time constant on pin 6 of IC2a prevents this register from also being reset at this stage. This is because the .01µF capacitor doesn’t have sufficient time to charge. IC2a now toggles again so that its Q0 output goes high, lighting up LED 1 again, and so the cycle continues. While this is happening, the 47µF capacitor charges until the voltage at pin 13 of IC1c drops to a logic low. At this point, the output of IC1c is held high regardless of the pin 12 input level and thus both IC2a and IC2b are reset. All LEDs are now turned off and the current consumption is down to only a couple of microamps, allowing us to do away with a power switch. Once the ROLL button is pressed, the circuit comes alive and the whole process begins again. Power is supplied by either a 6V or 9V battery. The supply line is de­ coupled via a 470µF capacitor which also supplies the current surges re- quired by the circuit when the LEDs are being driven. Construction All of the components for the Dual LED Dice are installed on a PC board measuring 102 x 112mm and coded 08105941. Before you begin any soldering, check the board thoroughly for any shorts or breaks in the copper tracks. These should be repaired with a small artwork knife or a touch of the soldering iron where appropriate. Once the board appears to be OK, you can begin by install­ing the wire links. Make sure that you follow the overlay wiring diagram so that they are installed in the correct place. Next up, continue on with the resistors and diodes, fol­lowed by the capacitors and ICs. As most of the components are polarised, be careful to make sure that they are installed cor­rectly. After that you can install the LEDs. This should be rela­tively straightforward since all of the LEDs face the same way. Finally, install the switch and the battery snap. You can use a 9V battery or a battery holder with four 1.5V AA cells (to give 6V). PARTS LIST 1 PC board, code 08105941, 102 x 112mm 1 snap-action PCB switch (S1) 1 9V battery snap 1 6V or 9V battery (see text) 4 10mm x 3mm tapped spacers Semiconductors 2 4093 Schmitt NAND gate ICs (IC1,IC3) 2 4015 dual 4-bit shift registers (IC2,IC4) 3 1N914 signal diodes (D1,D2,D3) 7 5mm yellow LEDs (LEDs 1-7) 7 5mm red LEDs (LEDs 8-14) Capacitors 1 470µF 16VW electrolytic 1 47µF 16VW electrolytic 1 33µF 16VW electrolytic 4 .01µF 63VW MKT polyester Resistors (0.25W, 5%) 3 1MΩ 2 1.5kΩ 1 68kΩ 6 1kΩ 4 10kΩ Miscellaneous Machine screws, solder, tinned copper wire. Testing Check your work carefully for any components which are incorrectly installed or for any solder splashes causing shorts between the tracks. Once everything looks good, connect up your battery and press the button. You should see the LEDs initially flashing quite quickly and then slow down to a complete stop. After about 30 seconds or so, the display should then turn off. You’ll need to do this a number of times to make sure that all the displays appear. If any LEDs fail to light up, check that you have them installed correctly. Note that for those LEDs which are in series with each other, you only need to have one installed incorrectly for both not to work. Cutting the board If you prefer, you can install this project in a plastic zippy box by cutting the board through the middle and then soldering wire links between the two boards to fold them over. This is best done before you start construction and will make the assembly that much smaller. OK, you’ve had your fun. Now you can get down to serious work with the SC board games. RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ No. 3 1 4 2 6 Value 1MΩ 68kΩ 10kΩ 1.5kΩ 1kΩ 4-Band Code (1%) brown black green brown blue grey orange brown brown black orange brown brown green red brown brown black red brown 5-Band Code (1%) brown black black yellow brown blue grey black red brown brown black black red brown brown green black brown brown brown black black brown brown May 1994  57