DIY Two Digit Counter Using 7-Segment Display and 555 Timer

A two digit counter is an electronic device that counts from 00 to 99 and displays the count on two 7-segment displays.

With each clock pulse, the displayed value increments, resetting to 00 after reaching 99. The first decade counter controls the units digit, while the second manages the tens.

This configuration is commonly used in digital clocks, event counters, and educational models to illustrate core digital electronics concepts.

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Two Digit Counter Circuit and Working

The device is built around an LM555 timer (IC1), two decade counter ICs (CD4033: IC2 and IC3), two 7-segment LTS543 displays (DIS1 and DIS2), and a few other components. This two-digit counter effectively counts in decimal format (from 00 to 99).

The LM555 timer (IC1) is configured as a monostable multivibrator that generates a pulse. This monostable output serves as the clock input for CD4033 (IC2). IC2 increments on every positive clock edge, providing an output to the 7-segment display.

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The LM555 timer prevents signal debouncing from the clock generated by switch S1 or a suitable sensor, ensuring a clean and precise clock pulse

The CD4033 IC is a decade counter that counts from 0 to 9. It features an inbuilt BCD output, providing the binary representation of numbers 0 to 9 on its output pins. The two CD4033 ICs are connected in a cascading configuration to enable counting from 00 to 99.

The first CD4033 IC (IC2) manages the one’s place. The clock pulse from the LM555 timer is fed into the clock input of IC2, causing it to increment by one for every pulse. The second CD4033 IC (IC3) controls the tens place. The carry-out pin of IC2 triggers IC3. When IC2 reaches 9 and resets to 0, it generates a carry-out pulse that triggers IC3 to increment the tens digit by one.

Each CD4033 IC provides BCD outputs corresponding to its count value (0-9). These outputs are fed to the 7-segment displays. The output of IC2 connects to the first 7-segment display (DIS1), which shows the current count for the one’s place. The output of IC3 connects to the second 7-segment display (DIS2), which shows the current count for the tens place.

When the device is powered on, pressing switch S2 momentarily triggers the LM555 timer, providing a clock pulse to IC2. Each pulse increments the count in the CD4033 ICs. IC2 increments the one’s digit, and when it overflows (reaches 9), it generates a carry-out signal that increments the tens digit in IC3. As a result, the two 7-segment displays count sequentially from 00 to 99.