This "Irreproducible Clock" Is Only Buildable If You Can Find the Same Retro PC Clock Speed Display

Engineer Ken Yap has produced a clock project with a difference: It's claimed to be "irreproducible," thanks to its use of an unusual display salvaged from an old desktop computer with manual "Turbo" button and clock speed display.

"It started when I looked at an integrated LED display in my junk^Wspares box," Yap writes. "This came from an old 386/486 era PC and could display the clock frequency up to 99 MHz. As installed it displayed only two speeds, normal and turbo, selected by a push button switch. A quirk was that the digits were yellow but the MHz (which would have been permanently lit) were in red. I liked the dual colors."

"I wondered if I could make a clock display out of this. With only two digits I would have to multiplex hours and minutes. It occurred to me that I could display 12:34 as 12 H, followed by 34M. There was another quirk and that was the MHz part only had 7 "segments". The vertical bars of the M were a segment each. The v in the middle was another segment. Similarly for the vertical bars of the H. However the middle bar was joined with the top of the z, and the final segment was the < of the bottom of the z. This meant that I would always have a "hyphen" after the H, so 12:34 would be displayed as 12 H-, then 34M. I will call this a feature."

The hardware is primarily salvage, with an STM8 microcontroller coded in SDCC and using a ported standard peripherals library for the firmware. It's assembled on perfboard — "it's ugly," Yap admits, "and even worse on the other side" — and while Yap has provided enough information to technically reproduce the build it is only likely to work correctly without modification if you happen to have exactly the same display from exactly the same vintage PC in your bits box.

Full details are available on the project's Hackaday.io page.