A DIY Digital Clock Made with Discrete Logic

When you consider what the time is, you may look at your phone, or the little display in the corner of your computer screen, but what if you had to design a timekeeping device from logic components? It’s a big job, but after a month of design, plus a month to actually build it, ‘ducamvinh’ has created his own digital clock from basic parts. 7-segment LEDs are used for the display, and components are mounted to a rather large circuit board, on display between two pieces of clear acrylic.

The clock includes six CD4026 ICs to control its number displays, along with a 74HC157 multiplexer. When each digit counter reaches its maximum, it’s then reset to zero, and this signal is passed on to the next IC. This adds one to the next display as appropriate, allowing it to show time in an easily readable HH:MM:SS format.

Timing is taken care of by a 32.786 kHz crystal and power is provided by a 5VDC barrel jack. There’s also a CR2032 battery onboard as a backup to keep it on track when power is temporarily cut off. Time is adjusted by two buttons, which act as manual timing signals to advance the hour and minute count, as well as a switch that resets the second counter and stops it from counting up.