A Digital Stop Watch built around timer IC NE555 and 4-digitcounter IC MM74C926 with multiplexed 7segment display. MM74C926 consists of a 4-digit counter, an internal output latch, npn output sourcing drivers for common cathode,7 segment display and internal multiplexing circuitry with four multiplexing outputs.
The counter advances on the negative edge of the clock. The clock is generated by the timer NE555. The circuit works of a 5 volt power supply. It can be easily assembled on a general-purpose PCB. Enclose the circuit in the wooden box with provisions for 7-segment displays, time varying switch S1, start/stop switch S2, and reset switch S3.