A digital stopwatch is an evergreen project, it can be done at any time no matter how our advanced our world’s technology is because nothing else can replace a stopwatch. And also this is a suitable hobby project for newbies. This is a simple p[roject which doesn’t require much expertise or components. The list of components for this project include;

  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

Description

A digital stopwatch built around timer IC LM555 and 4-digit counter IC MM74C926  with a 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 the 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 stopwatch 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).

After finishing this circuit, you can try building a long duration timer circuit (a fun circuit to build). You may check our category of clocks & timer circuits to try more circuits related to timing.

Digital Timer Circuit Diagram

Digital Stop watch circuit
Digital Timer Circuit

As I stated above, a digital stopwatch is a very fun circuit to build. After all, a stopwatch is something we have been fascinated by in our young days. Maybe the millennials won’t understand, but if you are someone from the middle of the 1970’s or 1980s, you will understand what I am saying. Enjoy building this circuit and have fun.

Author

72 Comments

  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

    • Pim Veld

      MM74C926 is not a clock-counter but a 4 decade ‘normal’ counter (from 0000 to 9999). If you want to count minutes and hours you have to use two ‘divide by 60’ counters.

    • Emmanuel M. Bauyon

      yeah. thesame as mine I dont know what to do to reset at 60 seconds. do you know the solution?

  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. i am also engineer of ETC….its great informative site…..good job..

  5. If any use of RTOS system in electronics industry. Please tell me.

  6. 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.

    • what can i use as a replacemeent for MM74C926

  7. 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?

  8. what can i use as a replacement for MM74C926??

    • Seetharaman

      It is a special purpose custom made IC has no replacement equivalent.

  9. Johary Ambalagan

    …were finally finished this project!!! but the IC is so expensive-

  10. sunilnadh

    IN OUR TO SUBMITT A MINI PROJECT I HAVE SELECTED THIS ONE
    PLS wish me to get success

  11. Renuka B. Khatke

    What will be the price of overall project.

  12. we dont get the ic mm74c926 let we know there is any replacement for it

  13. we dont get the ic mm74c926 let we know there is any replacement for it

  14. i would like to know how this circuit works????? anyone help me plzz

  15. How are the resistors connected to the 7-segments ?

    • 7-segment display as 7 terminal, no 15 port of the IC is connected to the “a” terminal of the 7-segment display through resistor. Like that all the terminals of the IC is connected to the respective terminals of the 7-segment display. TO know more about the terminals of the 7-segment display check this link http://en.wikipedia.org/wiki/Seven-segment_display.

      • Using raspberry pi GPIO pins to turn on a LED by giving high signal,and a switch as an input to turn it off.ith each time led ON it should increment the counter of 7 segment display , now the problem i m facing is that if i blink the led with a program it should reset the counter of 7 segment display using the same data lines . for doing this i have to make an additional circuit. kindly give some hints to proceed.

  16. 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?

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

  18. Siddheshwar

    sir is there any replacement for ic mm74c926?

  19. bharath4

    hi can i use any other ic’s instead of mm74c926.if there any plz reply me…….

  20. HI!!
    i’m makein this ckt on EAGLE.
    but m not understanding which switches to use.
    plz can you help me?

  21. 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 .

  22. 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 market.you 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.

    • RIPHAH INTERNATIONAL UNIVERSITY STUDENT:
      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

  23. pls tell me the applications of the chip used.how we can expand this project?

  24. 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.

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

  26. 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

  27. plz snd the question for oral exam on interval measurement using 74c926

  28. 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.

  29. i m not finding hw to cofigurate resistor with sevensegment…plz help me..

  30. 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.

  31. instead of using 74c926… can i use 74ls series of ic.??
    if yes,.what type of 74ls can i use.?

  32. Dear Friends,
    It is humbly requested that please show your any contact or email espacially email of gmail account becasue my email id is also in gmail so we can contact easily.

    Email salmanwaheed2008@gmail.com

    thanks.

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

  34. i want pcb design of digital stopwatch.please send me.

  35. I cant find mm74c926 in multisim too. what can i use instead of it ??
    Thanks

  36. sir, plz send me more details of itz component and a fine circuit plzz i will be vry thankful to u sir….

  37. i wanted the digital stop watch uing bcd’s and simple circuits

  38. i have to make it on multisim but i cant find mm74c926 in multi. what can i use instead of it ??

  39. MARK ANGELO

    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.

    • i couldnt get ic 74c926.is there any alternative…

  40. cesar peralta

    RESET PROBLEM: why won’t it reset when the timer is on stop mode?

  41. 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

  42. 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.

  43. 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?