Edit: Yeh, I know about the bug where the tens of minutes weren't ticking over correctly but it's fixed now. Schematic file updated.

This is a 24 hour digital clock using my 9 segment display for the digits. It uses unary counters to cycle through the states for each digit instead of a binary counter with a decoder. It keeps good time so long as the game doesnt lag causing the redstone ticks to run longer than a 10th/second. My experience, on a very underpowered laptop, it still manages to tick real time quite well.

The controls are on the display above the smaller second-digits.



Cyan button increases the hour counter; the first blue button increases 10s of minutes; the next increases single minutes (9 to 0 wont tick over the tens counter). Green starts the clock, red interrupts the clock and resets the seconds to 00.

Note about the schematic. The version of the clock in the schematic I filled with glass to prevent mobs spawning inside. The Clock is also under-lit to avoid the same thing.

Dokucraft Creative was the resource pack used for the screenshots.