555 timer ic

Digital Stop Watch Circuit


Since there’s no substitute for a stopwatch, a digital stop watch remains a timeless project that can be undertaken at any time, regardless of the level of technological advancement in our world. It also serves as an excellent introductory project for beginners. This is a simple project that doesn’t require an extensive amount of expertise or materials. The components for this project include the following:

  1. IC LM555 – 1 nos
  2. IC MM74C926 – 1 nos
  3. Resistors of various resistance values – 19 nos
  4. Reset switch – 1 nos
  5. Diodes – 6 nos
  6. 4 digit display
  7. Start-stop button
  8. Capacitors  – 2 nos


A digital stop watch featuring a multiplexed 7-segment LED display is centered around the LM555 timer IC and the 4-digit counter IC MM74C926. The MM74C926 includes a 4-digit counter, an internal output latch, NPN output source drivers for common cathode displays, a 7-segment display, and internal multiplexing circuitry with four multiplexing outputs. The counter advances on the negative edge of the clock signal.

The clock signal is generated using the LM555 timer IC. The entire circuit operates on a 5V battery power source. It can be easily assembled on a standard-purpose PCB. Place the circuit within a metal enclosure along with four 7-segment displays, a rotary switch S1, a start/stop switch S2, and a reset button S3 for user-friendly functionality.


To initiate the operation, press S3, resetting the circuit to display ‘0000.’ To commence the stopwatch and initiate time counting, activate switch S2. If you wish to halt the timer, simply deactivate S2. Rotary switch S1 is employed to select various time intervals at the output of the astable multivibrator (IC1).

Once you’ve completed this project, you may consider constructing a timer circuit for extended durations, which can be both fun and educational. For more circuits related to timing and clocks, you can explore our clocks & timer circuits category.

Digital Timer Schematic Circuit Diagram

Digital Timer Schematic Circuit Diagram

As mentioned earlier, building a digital stopwatch can be an enjoyable endeavor. After all, stopwatches have piqued our interest since childhood. While millennials may not fully relate, those who grew up in the 1970s or 1980s will certainly understand the nostalgia. Enjoy the process of assembling this circuit!


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