Make a Digital Stop Watch


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


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

Digital Timer Circuit Diagram .


                   Digital Timer Circuit

You may also be interested in other Timer
circuits we have in our website:

1-Long Duration Timer Circuit

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