Electronic Ludo Circuit
Timer IC 555 (IC1) is wired in the astable mode to produce clock pulse of very high frequency depending on the values of capacitor C1 and resistors R1 and R2, respectively. Pin 4 of IC1 is pulled to negative supply through resistor R3 to disable timer IC1.
When switch S1 is pressed momentarily, IC1 starts generating clock pulse. On releasing S1, IC1 stops counting. Output pin 3 of IC1 is connected to clock input pin 14 of binary decade counter IC 7490 (IC2). Output from pins 11, 8, 9 and 12 of IC2 is connected to BCD input pins 12, 13, 14 and 15 of 1-of-10 decoder IC 7442 (IC3). Output from pin 9 of IC3 is fed back to pins 2 and 3 of IC2 after inversion by inverter N2 to resets IC2 after every six counts. Outputs from pins 11, 8, 9 and 12 of IC2 are also connected to BCD input pins 6, 2, 1 and 7 of BCD-to-seven segment decoder/driver IC 7447 (IC5), respectively, to drive 7-segment common-anode display LTS542 (DIS1).
IC2 would normally produce binary code of ‘0’ to ‘9’ on sequential clock pulses provided by IC1 but output from pin 9 of IC3 resets it after every sixth clock pulse. The resulting count output is always between ‘0’ to ‘6.’ Diodes D1 and D2 form an OR gate and convert the first ‘0’ into ‘1,’ so the displayed count is always between ‘1’ to ‘6.’
The article was first published in September 2006 and has recently been updated.