Simple Digital Stopwatch Circuit

Often we need stopwatch to differentiate the time of two events. Here in this tutorial we are going to design a simple digital stopwatch circuit, without using any microcontroller. Here we have used the popular 555 timer IC, CD4033 ICs and few other components, which are listed below.

Required Components

• IC 4033 - 2
• 555 timer IC -1
• Common Cathode 7 Segment Display -2
• 150 Ohm -1
• 100K resistor -1
• 33K resistor -1
• 56K resistor -1
• 10uF capacitor -1
• On/off switch -1
• Push button  -1
• Bread board -1
• 9 Volt Battery -1
• Battery Connector -1
• LED -1
• Voltage Regulator 7805 -1
• Connecting wires

IC CD4033

This is counter and seven segment decoding in one package IC which is very easy to interface with seven segment displays. This is fully static counter operational IC and ideal for low power displays. This IC can be used for decade counting seven segment decimal displays, frequency division seven segment decimal displays, clocks, watches, timers, counter/display driver for meter applications.

Digital Stopwatch Circuit Diagram and Explanation

In this circuit we have used a 555 timer IC based astable multi-vibrator which is for creating 1 second delay. And two common cathode seven segment decoder IC’s namely CD4033. The output of astable multivibrator is directly applied to seven segment decoder IC’s (U4) Clock pin (1) and carry output pin(5) of U4 IC is directly connected to clock pin (1) of second seven segment decoder(U3). And two seven segment are connected with these decoder (U3 and U4). Its connections are shown in stopwatch circuit diagram given below. One push button is used to stop /start the stopwatch and one push button is used to reset the stopwatch. A 5 volt voltage regulator is used for providing 5 volt to whole circuit. And a 9 volt battery is used for powering the circuit.  Rest of connections are shown in the circuit diagram.

Working

In this stop watch circuit we have generated one second delay by using 555 timer based astable multivibrator. By using some calculation we can easily generates one second delay. In astable multivibrator there is two resisters and one capacitor is responsible for delay by charging or discharging capacitor through resistors. Calculation formula for generating delay for astable multivibrator is given below.

F=1/T= 1.44/(R1 + 2R2) C1

In this project we have selects R1 is 33K, R2 is 56K and C1 is 10uF. [Also check: 1 minute timer circuit]

Ass Astable multi-vibrator generates one seconds delay, this delay is oscillations or pulse of 0 and 1. So we will use this pulse for triggering the seven segment decoder then seven segment decoder changes the digit number with the one second of time period.

When we ON the stopwatch (by start/stop button) it start counting from zero and if we turned OFF the same button then counting is stop or pause until again turned ON the same button or press reset button.

There are two seven segments, so this stopwatch circuit can count 00-99 seconds time.