Digital Stop Watch

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 (IC1).

Digital Timer Circuit Diagram .

Digital Stop watch circuit

Digital Timer Circuit

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

1. Long Duration Timer Circuit

For more circuits, please check our category on Clocking and Timer Circuits

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68 thoughts on “Digital Stop Watch

  1. john muqattash

    Hi guys i built the circuit successfully however it doesnt reset at 60 senconds and instead continues to 99 does anyone have any soulutions

  2. john muqattash

    Hi i have built this circuit for testing purposes, however i find that the teansistors connnected to the 7 segment displays overheat alot and the 7 segment displays do not light up properly do u have any suggestions for the problems and any solutions? Thanks

  3. durga prasad

    hi sir,
    can i know which ic can be used to replace 74C926? Also can i know how resistors are connected to the 7 segment display?

  4. Mark Odyssey Rodel

    After making the circuit we encounter some problems, instead of just counting from 0-59 it continuous up to 99. Any idea how to fix this.

  5. iksir

    you know what, I’ve done with this by using 74C926. But, it’s just counting. When it’s 00.59, it just continue counting til 99. it should be 01.00 if it’s a stopwatch as you wrote at the title.
    do you know how to fix it?

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  7. zaini

    i’m done doing this stopwatch..but can’t operatingw well…the problem is cannot start….when reset,the LED show a number 8888…so what is the problem?

  8. parinay

    sir ,how we can assemble these project if we don’t know d procedure .so ,plz rply soon i wanna to module these……

  9. din

    hi, i am student of unikl miat located at sepang .. i learning mechanical and currently doing my fyp that need automatic digital timer or stopwatch. i really do have almost zero skill and knowledge obout this item. if u may .. could u pls elaborate this device for me . tq
    ur help are highly appreciated .

  10. Faisal

    HITEC UNIVERSITY STUDENT:I have Made digital stopwatch using this cct . and it is working properly.the problem is that IC2 is expensive (Rs 800) and its not available easily in can use any seven segment display but it should be common cathode. its above 3rd pin should be ground.2 pole 4 position rotary switch should be used pole is connected with 22k resistor and other any two terminals with position 1 and 2.disp1 in this cct of milli sec disp2 is sec disp3 is minute.ground should be given properly use small wires as you can for breadboard.

    • Usman

      AOA. i am using proteus to design the stopwatch. Can u tell me which tansistor to use? The bc547 bipolar or the NPN.
      Also from where did u buy the IC? I am assuming you are living in the Isl/Pindi region.
      Also how do I connect the 7 segment displays with each other?
      Plz reply soon

  11. sruthi

    plaese send me the required functions of the chip IC1 LM555,and IC2 MM 74C926.PLEASE INCLUDE WHY THE CAPACITANCE ARE IMPORTANT IN THIS CIRCUIT.

  12. ashraf

    i have made this circuit but its not counting..its showing 0000 reading but not counting..
    please help me

  13. Paul

    T1 is not listed on the parts list and T2 is there a suitable sub for this part? The 7 segment displays need pinout connections. Also part# for the 7 segment displays can’t be found is there a sub for this also. Thanks

  14. rutuja

    Plz snd the questions and answers of project on internal measurement using 74c926(digital stop watch)which will be asked for oral examination as early as possible.

  15. seetharaman

    Hi Asichi MM74C926 is an LSI with lots of digital circuits integrated into it. with discrete 741s you cannot build up the required circuit.

  16. pinky

    i have made this circuit but its not counting..its showing 0000 reading but not the 555timer is not working with LED but its absolutely okay
    plz help


    oh man… this circuit saved me from my subject,it really worked, and it impressed my instructor..

    it has two functions… the regular stopwatch and the split type.

    though the ic 74c926 type is expensive.

    i have pics on my facebook account of this project.

  18. joseph aranas

    sir, i tried this circuit of yours digital stop watch, and it works fine….thing is the hundredth of a second works, but when it comes in the minute counting, it doesn’t stop at 60 but goes to 99…what to do…please help…thanks

  19. phanindra

    how can digital stop watch works it is a MM74C926 decade coUnter IC how it could count i me to say a digital stop watch will count 60sec and then reset.

  20. chumisa

    since a 74C926 counter is not there when simulating the circuit for the stopwatch, can a up/ down counter be used instead of this one? or which counter can be used?


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