A real-time clock driving a multiplexed display. It's designed for a AT90s2313 and uses a cleaned-up 60Hz signal to drive the clock. It uses switches to set the hour or minute, and select between 12 and 24-hour mode.
I wrote this to convert a broken scale head unit into a clock. The unit was initially built in 1974 (judging from the chips date codes), has nifty Numitron tubes, and a nice, rugged case. I bought it at a government surplus shop near Washington, DC. A photo of the completed project is included. I gave it to my brother-in-law. He appeared to appreciate it.