• Skip to main content
  • Skip to primary sidebar

Homemade Circuit Projects

Need circuit help? Post them in the comments! I've answered over 50,000!

Blog | Categories | About | Contact | Calculators-online
You are here: Home / Games and Sports Projects / Simple Digital Stopwatch Circuit (4-Digit)
stopwatchcircuit

Simple Digital Stopwatch Circuit (4-Digit)

Last Updated on December 26, 2024 by Swagatam 50 Comments

In this article we'll study a digital stopwatch design configured around the very popular IC LM555 in conjunction with a 4-digit counter IC with multiplexed 7-segment output drivers (MM74C926).

Table of Contents
  • Circuit Operation
  • Circuit Diagram
  • Main Specifications of the IC MM74C926:
  • Pin Configuration:
  • Related Formulas:

Written and Submitted by: Jennifer Goldy

Circuit Operation

IC MM74C926 is internally made up of a 4-digit counter, an output latch up stage, a npn output responsible for sourcing driver networks for common-cathode, 7-segment display and an internal multiplexing circuitry with four multiplexing outputs.

The multiplexing circuit stage also includes an in-built free running oscillator, and does not rely on any additional external frequency generating network.

The counter is designed to proceed on a negative rising of the clock signals.

The clock signal is manufactured by the timer IC LM555 (IC1) and impressed over pin 12 of IC2.A higher signal on reset pin 13 of IC2 resets the IC to zero logic.

Reset pin 13 is associated with +5V by means of a reset push-on-switch S3.

The moment S2 is is pressed even for a fraction of a second, the count figure is rendered to a zero logic, transistor T1 responds with a trigger and it resets IC1.

This enforces the counting to start in a situation wherein S2 is in ‘off’ condition.

Circuit Diagram

warning message: electricity is dangerous, proceed with caution

A low logic signal on the latch-enable input pin 5 (LE) of IC2 latches the count in the counter module into the on chip set output latches.

In an event when switch S2 is switched ON, pin 5 is forced to go low and thereby the count figure is allowed to be saved in the latch section of the IC.

Display-select pin 6 (DS) ascertains if the figure on the counter or the stored count in the latch may be shown on the display or not.

In case pin 6 is held low the figure in the output latch section is enabled to get displayed, however if pin 6 is rendered with a high logic the count stored in the counter is illuminated over the connected display.

On an occasion when switch S2 is switched, the base of pnp transistor T2 is linked with ground ensuring that it begins operating. The emitter of T2 is rigged with DS pin of IC2.

Consequently, whenever switch S3 is switched ON, reset pin 13 of IC2 is coupled with negative through the transistor T1 making sure that the oscillator is inhibited from generating clock pulses. This operation is executed to implement a synchronization between IC1 and IC2.

At the first level, reset the module in order to enable the display to show ‘0000.’ Next disconnect switch S2 for the stop watch to initiate its counting the periods. In case you wished to inhibit the clocking of the chip, simply switch OFF the control S2.

The given rotary switch S1 may be opted for selecting the many different time intervals at the output of the astable multivibrator (IC1).

The proposed digital stopwatch circuit will work off a 5V supply inputs. The circuit may be easily fixed and built on a general-purpose PCB.

You may want to enclose the entire circuit in a metallic cabinet with slots built for four 7-segment displays, rotary switch S1, start/stop switch S2 and reset switch S3 in the dashboard plate of the selected encloser.

Main Specifications of the IC MM74C926:

  • Supply Voltage (Vdd): 3V to 15V
  • Logic Type: CMOS
  • Current Consumption: Low power due to CMOS technology
  • Clock Frequency: Up to 3 MHz at 10V
  • Output Type: Common cathode 7-segment LED display driver
  • Digits Supported: 4 digits (multiplexed)
  • Package Type: DIP or SOIC
  • Operating Temperature Range: -40°C to +85°C

Pin Configuration:

  • Clock (CLK): Input for incrementing the counter.
  • Reset (RST): Input to reset the counter to zero.
  • Latch Enable (LE): Controls data latching for display updates.
  • Display Outputs: Segment outputs (a, b, c, d, e, f, g) for driving a common cathode 7-segment display.
  • Digit Select Outputs (D1-D4): Used for multiplexing the 4 digits.

Related Formulas:

Frequency of Oscillation (Internal Clock) can be calculated using the following formula:

f = 1 / (Rt * Ct)

  • Rt: Resistor connected to the clock pin
  • Ct: Capacitor connected to the clock pin

Current through Segment LEDs can be calculated using the following formula:

  • Iseg = (Vdd - Vseg) / Rseg
  • Vseg: Forward voltage drop of the LED segment (typically 2V for red LEDs)
  • Rseg: Series resistor value for limiting current

Maximum Display Frequency (Multiplexing) can be calculated using the following formula:

  • fdisp = fclk / 4
  • fdisp: Effective refresh rate for each digit
  • fclk: Input clock frequency

You'll also like:

  • 1.  10 LED Simple Roulette Wheel Circuit Diagram
  • 2.  Electromagnetic Levitation Circuit [Anti-gravity]
  • 3.  5 Simple Fastest Finger First Circuits Explained
  • 4.  Electronic Scoreboard Circuit Using IC 4033 Counter
  • 5.  Tennis Ball Throwing Machine Circuit
  • 6.  Random LED Number Generator for Gambling Application

Filed Under: Games and Sports Projects Tagged With: Digit, Digital, Simple, Stopwatch

About Swagatam

I am an electronics engineer and doing practical hands-on work from more than 15 years now. Building real circuits, testing them and also making PCB layouts by myself. I really love doing all these things like inventing something new, designing electronics and also helping other people like hobby guys who want to make their own cool circuits at home.

And that is the main reason why I started this website homemade-circuits.com, to share different types of circuit ideas..

If you are having any kind of doubt or question related to circuits then just write down your question in the comment box below, I am like always checking, so I guarantee I will reply you for sure!

Previous Post: « Simple Digital Clock using LM8650 IC Circuit
Next Post: How to Interface Arduino PWM with any Inverter »
Subscribe
Notify of
guest
guest
50 Comments
Inline Feedbacks
View all comments

Primary Sidebar

circuit simulator image

Subscribe to get New Circuits in your Email

Categories

  • Arduino Projects (90)
  • Audio and Amplifier Projects (132)
  • Automation Projects (17)
  • Automobile Electronics (101)
  • Battery Charger Circuits (84)
  • Datasheets and Components (105)
  • Electronics Theory (140)
  • Free Energy (37)
  • Games and Sports Projects (11)
  • Grid and 3-Phase (19)
  • Health related Projects (25)
  • Home Electrical Circuits (12)
  • Indicator Circuits (15)
  • Inverter Circuits (89)
  • Lamps and Lights (142)
  • Meters and Testers (71)
  • Mini Projects (46)
  • Motor Controller (64)
  • Oscillator Circuits (28)
  • Pets and Pests (15)
  • Power Supply Circuits (89)
  • Remote Control Circuits (50)
  • Security and Alarm (64)
  • Sensors and Detectors (103)
  • SMPS and Converters (29)
  • Solar Controller Circuits (60)
  • Temperature Controllers (42)
  • Timer and Delay Relay (49)
  • Transmitter Circuits (29)
  • Voltage Control and Protection (38)
  • Water Controller (36)

Other Links

  • Privacy Policy
  • Cookie Policy
  • Disclaimer
  • Copyright
  • Videos
  • Sitemap

People also Search

555 Circuits | 741 Circuits | LM324 Circuits | LM338 Circuits | 4017 Circuits | Ultrasonic Projects | SMPS Projects | Christmas Projects | MOSFETs | Radio Circuits | Laser Circuits | PIR Projects |

Social Profiles

  • Twitter
  • YouTube
  • Instagram
  • Pinterest
  • My Facebook-Page
  • Quora
  • Stack Exchange
  • Linkedin
  • Recent Comments

    • Swagatam on How to Convert a Low Power Inverter to a High Power Inverter
    • Swagatam on Simple Buck Converter Circuits using Transistors
    • NGANG on How to Convert a Low Power Inverter to a High Power Inverter
    • Swagatam on Make this 7 Segment Digital Clock with Beep Alert Circuit
    • Swagatam on Make this 7 Segment Digital Clock with Beep Alert Circuit

    © 2025 · Swagatam Innovations