Electronic Circuit: Digital Stopwatch

● This digital stopwatch circuit can be worked as a clock in this counter will advance after every one second. When you provide power supply it start its counting from zero and you can stop the timing with the help of switch.

● It can be used while cooking or while doing exercise.

● It can used by students preparing for competitive exams.

● You can also use this digital stopwatch circuit during playing game like teams have to complete the task and the team which have done it in shortest period of time first will be the winner. In such type of game we can easily record the time of individual team. In this the team which finishes the task just have to flip the switch S2 and time get recorded.

● This circuit also calculate the time in minute. In this circuit when 99 seconds completed a musical sound is heard and it will sound till 50 seconds and stop again for approx. 40 seconds. So when alarm sounds and stop sounding in total 1.5 minutes approx. is completed. You can also off the musical sound with the help of switch S1.

● In this stopwatch circuit you do not require to see the clock for timing you can calculate it by hearing the musical sound. This is helpful while playing the game.

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Fig. 1: Prototype Of Digital Stopwatch Circuit On Breadboard

This digital stopwatch circuit is based on two IC namely NE555 and CD4033 with few more discrete component. CD4033 is a Johnson counter IC commonly used in digital display. It has a 5 stage Johnson decade counter with decoder which convert the Johnson code to a 7 segment decoded output. Means it will convert the input into numeric display which can be seen on 7 segment display.

And in this circuit NE555 astable generates a clock for the circuit, which provide a oscillating wave to the output pin 3 of IC1. The time period of counter can be calculated by following formula-

T = 0.7 (R1 + 2*R2)*C1

Assemble the circuit properly. Connect the pin 3 of both the IC1 and 2 to supply, to on the display. If pin 3 is connected to ground we will not get display on 7 segment output. And also connect the pin 15 which is a reset pin to ground so that when counting reaches to 99 it will reset the counter to zero. Pin 2 of IC1 and IC2 is known as clock inhibit pin if this pin is held high then counter will not advance in spite of clock pulse. That’s why we have connected this pin with the help of switch S2 to stop the counter whenever it is required by the user. And if you again flip this switch your counter will start counting again from where you have left.

Now apply power supply. Zero will be displayed on both the 7 segment display. And counter starts counting by receiving pulse from IC3. As NE555 is wired in astable mode it is generating continuous pulses which make the clock pin 1 of IC1 high after every specific period of time. After receiving the clock pulse 4033 IC counter advances and 1 will be displayed on common cathode 7 segment display. When second pulse is encounter same phenomenon occurs and 2 is displayed till count reaches 9.

When it reaches 9 one cycle is completed. As you can see from circuit diagram pin 5 of IC1 is connected to pin 1 of IC2 to cascade another IC, after every 10th pulse it will go high to provide a clock pulse to IC2 to advance its counter that’s why we will receive a 1 on 7 segment common cathode display 2 .

And we have connected the pin 5 of IC2 to a switch which will control the alarm circuit so after every 100th pulse it will go high and alarm will sound. Which you can stop by flipping the switch S1. We have used UM66 IC for producing sound which are amplified by transistor T1 and hear with the help of speaker.

Unit place number are displayed on display 1 and tens place numbers are displayed on display 2. After completion of each cycle tens place advances one. Similarly you can add N numbers of 4033 IC with 7 segment display.