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WHICH CLOCK? A BINARY CLOCK! Which clock tells the time yet has no hands, face or digits? Which clock counts off the time in inexorable fashion & is almost hypnotic as you watch it? Which clock painlessly teaches binary numbers & tells the time too? A binary clock, of course! Design By MICHAEL VOS* This clock uses 17 large LEDs to display the time in binary fashion. Anyone who sees it remorselessly counting away cannot help being intrigued. And while we don’t think it will suddenly dis­place conventional clocks and watches, it presents a different and interesting way of telling the time. And it can be used to teach the system of binary numbers. In a binary clock, six digits are required to display sec­onds or minutes. In other words, we need a 6-bit system with each bit weighted according to its position in the sequence. So with six bits or six LEDs we can display any number between zero and 63. In 70  Silicon Chip practice, for a binary display of minutes or seconds, we only count from zero to 59. To display hours, we need only five bits (or LEDs) since we need only count up to 23. This clock will display 12 or 24-hour time. Circuit description Since this clock counts in binary rather than decimal, it is ideally suited to logic circuitry. However, rather than use standard logic ICs, the designer has opted to use GALs from Lattice Semiconductors, Inc of the USA. GAL stands for Generic Array Logic and is a variant of the programmable logic array devices produced by a number of semiconductor companies. In effect, GALs, PALs, PLAs or whatever they are called, can be programmed by fusing internal links so that arrays of gates can be made to perform a wide variety of functions. In effect, they give the advantage of custom ICs without the design and manufacturing expense. Three GALs have been used in this circuit and they have been individually programmed to provide the seconds, minutes and hours counters. Each of these counters can be pre-loaded with a value using a set of DIP switches and this provides a method of setting the time. With GALs providing the basic time counting circuitry, it only remains to provide a 1Hz pulse signal and this is provided by IC3 and IC4. One inverter inside IC3, a 74HC4060 ripple counter, is connected with a crystal to oscillate at 4.194304MHz. The crystal is temperature compensated with the ceramic capacitors connected to pins 10 and 11. This clock frequency is divided by 256 and 1.2k 1% VR1 500  OUT IC8 LM317T 120  ADJ 1% 100k VCC 6.8 25VW 1 ZD1 4.3V 2 3 4 IN 5 6 S5 S4 S3 S2 S1 S0 S1 SECONDS 12 11 10 9 8 7 I1 I2 I3 1 2 3 5x 0.1 IC5 OUT 7805 GND 6.8 GND 25VW 6 5 7 4 8 J1 DC3 BINARY CLOCK D1 1N4001 6.8 25VW 1 2 IN 3 12 11 10 9 M5 M4 M3 M2 M1 M0 S2 MINUTES I1 I2 1 2 IOR1 K A 6 IC8 IC5 I GO 8 IC7c 11 10 I3 10k 11 IC7a 2 7 3 IC7b 5 RUN SET S4 10k 10k VC1 30pF 33pF 56pF X1 4.1943MHz 10M PO 10 8 RST 12 PI 11 4 14 6 74HC00 VCC 8 14 Q8 IC3 74HC4060 33pF N750 12 12 RST 12 3 Q14 11 11 PI IC4 74HC4060 16 16 VCC 13 13 IC7d 3 20 AO I 5 4 3 2 1 16 IOR4 12/ H4 H3 H2 H1 H0 24 12 11 10 9 8 7 9 I1 I2 IOR1 1 2 19 10 S3 HOURS IOR8 K 15 IOR5 IC2 GAL16V8B  K 8 K 17 IOR3 A 4  16 LED1-5 18 IOR2  K 2 A  1 K 14 IOR6  A 1k 1k A 1k 1k A I4 I5 I6 I7 I8 I9 I10 4 5 6 7 8 9 11 12 9VDC 20 VCC 19 18 IOR2 K 17 IOR3 10 16 IOR4 IC1 GAL16V8B 14 IOR6 K 15 IOR5 K  K 4  K 16 I4 I5 I6 I7 I8 I9 I10 4 5 6 7 8 9 11 IOR8 1 K 13 IOR7  12 19 18 IOR2 20 VCC IOR1 K 17 IOR3 K 16  10 I4 I5 I6 I7 I8 I9 I10 4 5 6 7 8 9 11 12 IC6 GAL16V8B 14 IOR6 16 IOR4 K 4 K 15 IOR5 K  A 2  A 8  32 A  A 2  A 8  32 Construction Assembly of the clock is just a matter of installing all the components on the PC board. This should be cleaned and thor­oughly inspected before you begin inserting components. Install all the resistors, diodes and the zero-ohm link first, then insert the crystal. Tin the case end of the crystal with solder, install a discarded component pigtail lead through the PC board hole at the crystal end. Solder the wire to the crystal and PC board. This provides a ground shield, mechanical stability and thermal coupling to the capacitors. Next, install the trimmer capacitor. The flat end goes to the left. This orientation grounds the rotor so you can use a screwdriver without affecting frequency adjustment. Both 3-terminal regulators are mounted on the copper side of the PC board and their mounting tabs are bolted to the board for heatsinking. Install the three DIP switches (S1,S2,S3) so the individual switch numbers are on the bottom and read from left to right. The momentary pushbutton switch can also be installed at this stage. IOR8  K 13 IOR7 A  1 1k A 1k 1k A 1k 1k 1k LED12-17 A 1k A 1k 1k A 1k 1k 1k LED6-11 A the output at pin 14 is 16384Hz. This is divided by IC4, another 74HC4060 ripple counter, to provide an output signal of 1Hz at pin 3. The outputs of the GALs directly drive the 17 LEDs from a supply rail which is adjustable to provide variable display brightness. The variable supply is provided by IC8, an LM317T adjustable 3-terminal regulator. Its ADJ terminal can be adjusted from zero to 4.3V, as set by the zener diode ZD1, and thus its output can be varied from +1.2V to +4.9V. IC5, a 5V 3-terminal regulator, powers the rest of the cir­cuitry and diode D1 protects both regulators from reversed input supply connections. Power is provided by a 9V DC plug­pack. 1k ▲ Facing page: own a binary clock & be one up (two up) on your neigh­bours who have to make do with digital or analog clocks. 17 large LEDs indicate the time & they are driven by GALs (Generic Array Logic ICs). Fig.1: the circuit is essentially in two parts: (1) an oscillator & divider chain to produce a 1Hz signal; & (2) three GALs in a synchronous counter. October 1993  71 Install the 17 LEDs carefully so that they are aligned with each other. The shorter lead of each LED goes towards the GAL ICs. Install ICs 3, 4 and 7 and then the GAL ICs. Note that these are individually programmed and are coded with paint dots on their undersides. IC1 has one paint dot, IC2 has two paint dots and IC6 has no paint dots. If desired, the PC board can be mounted on an aluminium stand using the screws which retain the two 3-terminal regulators. This is available as an option with the kit. Install a PCB mount DC socket if you want power entry from the component side of the board. Alternatively, if PARTS LIST 1 PC board, 303 x 101mm 1 9V 500mA DC plugpack 1 2.1mm DC socket 1 aluminium stand (optional) 3 6-way DIP switches (S1, S2, S3) 1 momentary contact SPDT switch (S4) 1 4.1943MHz crystal 1 500Ω trimpot (VR1) Semiconductors 3 GAL16V8B 15ns ICs (IC1, IC2, IC6) 2 74HC4060N ripple counters (IC3, IC4) 1 74HC00N quad NAND gate (IC7) 1 LM7805T 5V regulator 1 LM317 adjustable 3-terminal regulator 17 10mm red 200mcd LEDs (LED1-LED17) 1 1N4001 1A rectifier diode (D1) 1 79C4V3 4.3V 400mW zener diode Capacitors 3 6.8µF 25VW tantalum electrolytic 5 0.1µF 50V monolithic ceramic 1 56pF N1500 ceramic 1 33pF N150 ceramic 1 33pF N1500 ceramic 1 2-30pF N750 ceramic trimmer Resistors 1 10MΩ 1 100kΩ 3 10kΩ 1 2.2kΩ 1 1.2kΩ 17 1kΩ 1 120Ω 1 0Ω link 72  Silicon Chip This photograph shows how the 3-terminal regulators (in this case the 7805) are mounted & fitted with insulated standoffs for mounting the board on the optional aluminium stand. Also shown is the panel-mounting DC power socket. your are using the aluminium stand, you will need to use a panel-mount DC socket and wire it to the PC board. Testing Rotate trimpot VR1 fully anti-clockwise and apply 9V DC to the board from a plugpack or power supply. Check that the LM7805 regulator output is +5V ±5%. Check that the trimpot varies the LM317 regulator output from +1.25V to +4.9V ±10%. With the trimpot fully clockwise to give full LED bright­ness, you should see the seconds LEDs change every second. Set all the DIP switches to the position marked “ZERO”. Press the pushbutton and all the LEDs should Specifications Clock time reference 4.194304 MHz quartz crystal. Accuracy ±1 second per 48 days when calibrated to within ±1Hz at 25°C. Worst case unadjusted: ±1 second every 11 hours based on ±100Hz deviation. Adjustment range Approx. ±100Hz. Clockwise adjustment of trim­mer capacitor speeds up clock. Operating temperature 0 to +50°C. Storage temperature 0 to +85°C. Power source 9V DC plugpack <at> 340mA min. 2.1mm DC2 type connec­tor. Brightness control Variable from 0 to 30mcd per lamp. Where to buy the kit 1.2k LED16 2 1k LED15 4 1k LED14 8 1k LED13 16 S4 1 10k 10k 10k 33pF 1k IC6 GAL16V8B 1 LED12 32 0 S1 1 1 0.1 1 1k LED11 1 1k LED10 2 1k LED9 4 1k LED8 8 1k LED7 16 0 S2 1 1 0.1 1 1k LED6 32 S3 1 1 0.1 LED5 1 1k LED4 2 LINK IC4 74HC060 1k 0 1 33pF VC1 0.1 TP 56pF LED3 4 1k LED2 8 1k 2.2k 10M IC3 74HC060 1k X1 1 0.1 LED1 16 6.8uF 100k 6.8uF 7805 D1 GND DC3 J1 Fig.2: the three GAL ICs are individually programmed & are coded with paint dots on their undersides. IC1 has one paint dot, IC2 has two paint dots & IC6 has no paint dots. The two 3-terminal regulators are mounted on the copper side of the PC board. 1k ZD1 120  IC7 74HC00 1k LED17 1 Setting the clock Setting the clock is a process of first setting switch 1 of DIP switch S3 for 12 or 24-hour mode. This done, set the hours, minutes and seconds for the appropriate time and press and hold the pushbutton until that occurs. This can be done while you are listening to the Telecom time signal. Having set the time, continue to check the time signal to ensure that the clock is in synchronism. You can use the decimal equivalent number shown under each LED to work out the DIP switch settings for any value between 0 and 63. The seconds and minutes are each set using six switches, while five switches are used for the hours setting. Note: the clock counting logic does not check for valid time settings and/or valid modes on the switches. It is possible to set the minutes and seconds to a maximum of 63 decimal, while the hours can be set to a maximum of 31 decimal. If these times are indeed set up on the switches, the clock will count until it reaches maximum, then SC resets to zero. VR1 6.8uF IC1 GAL16V8B 1 DOT go out. Now set each DIP switch to the position marked “ONE” and press the pushbutton. All LEDs should light up. Set the mode DIP switch (on S3) to “12”, set the DIP switches for a time of 12:59:59, press the pushbutton and one second later the LEDs should read 1:0:0. Set the mode DIP switch to “24”, leave the same time on the other switches, press the pushbutton and one second later the LEDs should read 13:0:0. Set the time DIP switches for 23:59:59, leave the mode DIP switch at “24” , press the pushbutton and one second later the LEDs should read 0:0:0. If you have a frequency counter you can adjust the crystal exactly to frequency although the board should be allowed to run for at least an hour before the adjustment is made. Connect the frequency counter to TP1. Adjust the trimmer capacitor to set the frequency at 4.194304MHz. Note that the initial accuracy will only be as good as your frequency counter. If you do not have a frequency counter, setting the crystal for best accuracy will be a process of trial and error, by com­paring the clock with VNG or Telecom time signals. LM317 IC2 GAL16V8B 2 DOTS The complete kit for the Binary Clock, including PC board, large LEDs and programmed GAL ICs, is available for $75 plus $5 postage and handling from Prototype Electronics, 1/29 Stewart St, Parramatta, NSW 2150. Phone (02) 683 3510 or Fax (02) 630 3148. The optional folded aluminium stand is also available at $25. Note: The above price does not include a 9V DC plugpack. October 1993  73