new design for India. Before I agreed to his proposal, he gave me the follow- ing specifications:
1. There should be two indepen- dent clocks for both the players.
2. The umpire should be capable of resetting the clocks to a reference time. 3. After thinking and playing the move, the player should operate a le- ver to stop his own clock and at the same time start the opponent’s clock.
4. There should be a facility to watch the movement of the clock also. 5. If either of the player takes more than 150 minutes to complete all the moves, there should be a time-out indi- cation.
6. The clock should be an accurate and reliable one.
Principle
With the above specifications in mind, a block diagram was drawn, as shown in Fig. 1. To have an accurate and reliable time, a quartz-controlled master oscillator is utilised to provide the drive for the clocks. It will supply the drive to either a Black Clock or the White Clock. The reset switch will bring the clocks to 000. With the help of switch S2, an alarm at 2:30 hours has to be set before the start of the match in each clock. A common piezo buzzer will sound after the lapse of
150 minutes by either of the player. The dot in the running clock will be blinking as the second’s indicator. This way, it may meet all the above-men- tioned specifications.
Circuit diagram
The complete circuit diagram of the chess clock is shown in Fig. 2. The commonly available 40-pin ICs, LM8361 or its equivalents, are used for identical Black and White clocks. The IC MM5369 along with the quartz crystal is used as the Master Oscillator, which supplies 60Hz drive to the clocks. The operation of switch S8 will cut off the drive from one clock and extend to the other clock. As the clock is generally required for two hours and 30 minutes, three-digit display is ad- equate.
Alarm outputs are ORed through two diodes and directly extended to the trigger terminal of a piezo buzzer.
Reset switch Sl extends the Vcc to
SLOW SET, FAST SET and SEC. DISPLAY
(i.e. pins 33,34 and 32). This will reset the clock having drive. Hence, both the clocks can be reset to 000, one by one by operating switches Sl and S8. Please, note that pins 38 of IC2 and IC3 are connected to Vcc, which makes the clocks run in the 24-hour mode. If pin 38 is kept open, the clock will run in a 12-hour mode and, while resetting, the clock will reset to 12:00 hour.
Using diodes D5 and D 12, it utilises the same switches S3 and S2 for ALARM DISPLAY/ALARM OFF functions of Black
and White clocks, respectively. The power is provided through a conven- tional 12-0-12 volts transformer and full-wave rectifier. The 9-volt battery provides the backup during power in- terruptions, if any. Hence, there are two buses of supplies. Vcc (A) has battery backup whereas Vcc (B) does not have battery backup. Total current drain is about 300 mA at 12 volts.
Assembly
The complete circuit shown in Fig.2
DIGITAL CHESS CLOCK
S.BATRA
Fig. 2: Circuit diagram for the digital chess clock.
Fig. 4: PCB layout for the display.
Fig. 6: Component layout for the PCB shown in Fig. 4. Fig. 5: Component layout for the PCB shown in Fig. 3.
can be easily wired on two PCBs meas- uring about 12 cms x 10 cms and 12 cms x 3 cms. The actual-size layout of both the PCBs is shown in Figs. 3 and 4, respectively.
The PCBs are designed in such a way that the segment outputs from clock PCB are in exact alignment with the segment of display PCB, which can be mounted above the clock PCB at right angle. Extra room in the clock PCB will make the assembly more comprehensive and even the trans- former, piezo buzzer, etc can be mounted on the clock PCB itself.
First of all, check all the compo- nents with the help of a multimeter. To start with, assemble the display PCB with the six display chips. With the help of 9-12 volts test bench power supply through a 1 -kilohm series resis- tor, check whether all the segments are glowing properly.
Now assemble the clock PCB. Sol- der all the resistors and check them subsequently. Then solder all the di- odes and finally all the three ICs. Con- nect display PCB and clock PCB with 43 fine wires at right angle and solder them. Connect the flexible wires of about 15cm length to the clock PCB for various switches.
Testing
Extend the power and test the complete circuit. As soon as the power is switched on, the clock receiving the drive may start blinking. Press the re- set switch and the clock will reset to 000. Turn switch S8 to another posi- tion and reset the second clock as well. With the help of SLOW SET and FAST SET switches, check the working
of both the clocks. Check that the sec- onds ‘dot’ blinks for the clock which is ‘on’ and does not blink for the clock which is ‘off’.
Now, set the alarm and see that it sounds at the desired time for both the clocks.
The complete assembly can be housed in an acrylic cabinet. All the switches should be mounted on the top side of the cabinet for the sake of con- venience. Further, care may be taken that SLOW SET, FAST SET and RESET
switches of both the clocks are not pro- jected outside the cabinet, and they are accessible only through a pen/pencil. This will prevent their accidental press- ing by anyone, and hence the time will not be disturbed.