- A digital stop watch built around timer IC LM555 and 4-digit counter IC MM74C926 with multiplexed 7-segment LED display.
- MM74C926 consists of a 4-digit counter, an internal output latch, npn output sourcing drivers for common cathode,
7-segment display and an internal multiplexing circuitry with four multiplexing outputs.The counter advances on negative edge of the clock. - The clock is generated by timer IC LM555.The circuit works off a 5V power supply. It can be easily assembled on a general-purpose PCB. Enclose the circuit in a metal box.
- with provisions for four 7-segment displays, rotary switch S1, start/stop switch S2 and reset switch S3.
TESTING: - First, reset the circuit by pressing S3 so that the display shows ‘0000.’
- Now open switch S2 for the stop watch to start counting the time. If you want to stop the clock, close S2.
- Rotary switch S1 is used to select the different time periods at the output of the astable multivibrator (IC1).
