LED Stop Watch Circuit

ICs 555 and 4017 are well-known to electronics hobbyists. Presented here is a very interesting project of an LED stopwatch Circuit using timer 555 and decade counter 4017 ICs. This stopwatch is able to monitor time from one second to 60 minutes. It can be used in sports, laboratories, etc.

IC 555 (IC₁) is the heart of the circuit. It is used in astable multivibrator mode. The special feature of this mode is that if this pin 4 of IC₁  is kept at a high logic, it produces a clock pulse normally but as soon as pin 4 gets low-level logic, it stops generating a clock pulse and the output stays at a low level.

In this circuit, pin 4 of IC₁  is wired to the ground through a 10 KΩ resistor, and push-to-on switch SW₁ is provided across the positive supply and pin 4. As soon as switch SW₁ is pressed, IC₁ starts generating clock pulses and the whole circuit gets activated.

AT each clock pulse, IC₂, IC₃, IC_4, and IC₅ start counting which is indicated by glowing LEDs. When switch SW₁ is released, IC₁ stops generating clock pulses and all counter ICs stop counting. The positions of all glowing LEDs will show how much time (pushing time of SW₁) has elapsed.

IC₂  counts for 1 to 10 seconds, IC₃  counts for 10 to 60 seconds, IC₄ counts for 1 to 10 minutes, and IC₅ counts for 10 to 60 minutes. Preset VR₁ should be adjusted so that IC₁ produces one full clock cycle in one second.

PARTS LIST LED STOP WATCH CIRCUIT

Resistor (all ¼-watt, ± 5% Carbon)

R1, R2, R4, R5 = 10 KΩ R3 = 22 KΩ VR1 = 100 KΩ

Capacitors

C1 = 10 µF, 16V (Electrolytic Capacitor) C2 = 0.01 µF (Ceramic Disc)

Semiconductors

IC1 = NE555 (Timer IC 555) IC2 – IC5 = CD4017 (Decade Counter IC)

Miscellaneous

SW1 = Push-to-on switch LEDs