Electronics Lucky Number

The circuit is simple and self explanatory. IC1, a NE555 timer, is used as astable mode to generate clock pulses at a rate of about 20 Hz. The frequency can be varied with the help of potentiometer VR1.

The clock pulses from the timer are fed to clock input of IC2, a decade counter. The outputs of the counter are decoded by IC3, (BCD to seven segment decoder/driver) which drives a common anode display (DIS1) to show from figure 0 to 9.

On pressing switch SW1, IC1 starts working, with the display changing from 0 to 9. Capacitors C1 is charged during this time.

ectronics lucky number

Once SW1 is released, the capacitor discharges through resistor R3, VR1, R1 and R2. Thus, the frequency of IC1 decrease (and hence the rate of changing figures on the display) and ultimate becomes zero, once C1 has totally discharged thereby stopping the displayed is enhanced by the time for which SW1 is pressed. So, the random effect is natural outcome.


Resistors (all ¼-watt, ± 5% Carbon)

R1 = 100 KΩ

R3 = 1 KΩ

R4 – R10 = 330 Ω

VR1 = 100 KΩ


C1 = 47 µF/10V

C2 = 0.47 µF

C3 = 0.01 µF


IC1 = NE555

IC2 = 7490

IC3 = 74247

D1 = 1N4001

DIS1 = FND507 or LTS542


SW1 = push to on switch

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