Discrete Clock Design Uses 74xx IC Logic Chips and 7-Segmented Displays

This retro-style timepiece utilizes 4-bit 74HC161 ICs and a 1Hz clock module to count hours, minutes, and seconds.

Cabe Atwell
2 months agoClocks

A lot of great projects have been made using TTL and CMOS logic ICs, including building a 4-bit CPU, an electronic piano, and an AM radio transmitter, to name just a few. Stephan's 74xx Discrete Clock is another great build that makes use of those old TTL chips and 7-segmented displays.

"The clock uses 4-bit binary counter ICs (74HC161) for counting hours, minutes and seconds, which are interconnected in a classic ripple-carry scheme."

The electronics for the timepiece are pretty basic and consists of six programmable counter modules, six 1Hz counter modules, six 7-segmented displays and display board, and a motherboard that connects them all. The output of each counter is decoded to drive the displays, while the motherboard provides power and interconnects the counter modules with one another. It also connects to the display board, which contains the decoders that drive the displays as well.

Each counter module needs to be programmed according to their position, which he explains, "For example, the counter driving the 10^0 seconds displays always counts to 9 before overflowing. The 10^1 seconds display's counter module always counts to 5 and so... (anybody already wondering?)."

Time is configured by pausing the clock via an enable switch, while a reset button clears all the counters, and an increment button increases each display digit. Stephan has uploaded a detailed walkthrough of his 74xx Discrete Clock on GitHub, complete with schematics for each module, for those interested in recreating his device.

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