Years ago I rescued an old, two-faced Simplex clock from a dumpster. It is a so-called slave clock: it has no time-keeping mechanism from itself but it receives a 24 volt pulse from a remote master clock once every minute.

Not having rescued the master clock I had to make an hour myself. The first version consisted of a 32.768 kHz chrystal, a 4060 binary counter, a 555 integrated circuit, and some assorted TTL ICs. The idea was to divide the 32.768 kHz time base from the chrystal by some factor and end up with one clock pulse per minute.

This version broke down after 16 years of good service: the rectifier, transformer and probably some other components burnt out for reasons I have not been able to discover. Unfortunately I lost the original schematic and I did not feel like reverse engineering it, so I had to make a new hour from scratch.

I wanted to do it differently this time: in stead of using the frequency of a chrystal, which is prone to temperature-induced drift, I chose to use the frequency of the mains power supply. This frequency can fluctuate in the short run, but the fluctuations cancel each other out over time, so over longer periods of time it is a stable 50 Hz. No need to adjust the clock but twice a year for summer- and wintertime.