The circuit presented here counts from 00 to 99 and displays it on two seven segment displays. It can work as free running counter in auto mode or it can count manually when button is pressed. In auto mode it gets continuous pulses and counts continuously at a rate of 1 Hz. That means the count is updated at every second or in other words counter displays time in seconds. This counting rate can be changed by changing pulse frequency. In manual mode, the count is incremented when push button is pressed manually. So it can be used to count up to 100 (from 0 to 99) as per manual requirement.
The counter circuit is made up of decade counter cum display driver chip CD4026. The pulse circuit is build using IC555. The circuit can be used in many applications like object counter, frequency counter, RPM counter, stop watch timer, token count display and many others.
As shown in Circuit Diagram figure, the major components of circuit are IC555, decade counter cum display driver CD4026 and common cathode type 7 segment display.
It is used to generate pulses. In auto mode it generates continuous pulses. In manual mode it generates pulses when push button PB1 is pressed. IC555 connections are made in such a way that when SW1 is in auto position, it is configured in astable mode. The timing components R1 C1 are adjusted such that IC555 generates pulses at a rate of 1 Hz. The frequency can be varied using pot R1. Now SW1 position is changed to manual, IC555 will be configured in monostable mode. Now IC555 gives high output pulse when push button is pressed. The LED at the output of IC555 indicates pulse output. Check out more circuits on 555 Timer IC
Decade Counter cum Display Driver CD4026
Decade counter chip CD4026. It increment it count by 1 on every pulse input. Also it converts the count into equivalent 7-segment display code (common cathode) so that count can be displayed. It counts from 0 to 9 and again resets to 0. When it goes from 9 to 0, it generates output pulse (carry out) that can be given to next decade counter chip. So as shown in figure the carry out (pin 5) of 1st decade counter chip. The outputs of both decade counter chips (CD4026) are a, b, c, d, e, f, and g that can be directly given to respective inputs to common cathode type 7 segment displays.
7 Segment Displays
The outputs of chip CD4026 are connected to a-b-c-d-e-f-g inputs of both 7 segment displays as shown. As the count increments it is displayed on these displays from 00 to 99 and again 00. Because they are common cathode type displays, their common terminals are grounded.
Free Running Counter
When switch SW1 is in auto position IC555 generates continuous pulses at 1 Hz. So counter is incremented at every second. Both displays show the count. The counting speed can be increased or decreased by varying pot R1. Normally pot R1 value is fixed to generate output of 1 Hz because it increments counter every second. So the counter can be used to display the time elapsed in seconds – maximum upto 100 second = 1 minute and 40 second. So in this mode this circuit can be used as stop watch timer that can be used to keep track of running events.
When switch SW1 is in manual position, IC555 generates pulse when push button is pressed. So the count is incremented when button is pressed manually. So this is simple manual counter that counts from 0 to 99 (100 counts) as user presses a switch. So in this mode the circuit can be used as token number display. Token number system is widely used in banks, restaurants and many such public places. One can connect the output of any sensor (like LDR or photo diode etc) instead of push button to give trigger input to IC555. In that case the counter can count any external event or objects or RPM etc.