Revive a railway clock

Since few summers ago I have kept my eye on a popular bidding site. I was attracted by a few German railway clocks (as a less-famous brother to their Swiss counterpart). I have since brought several, some even have second hands (not synchronised though), and rescued them from the brutal conversions by the greedy vintage dealers. I then also buy the British ones, which are mechanically much more fun. These dealers normally buy these clocks at around £30 and try to sell them over £100 after converting the slave movements to quartz — and people buy them!? I would not stand such behaviour, so I took the problem to my own hands, aiming to save the whole clock with a cost under £20. Inspired by a similar project from veeb.ch, I decided to make a more robust and reliable code.

Materials

• Clock electrically and mechanically working
• Raspberry Pi Pico W
• Cables
• Power supplies
• Converters
• (additionally if you wish) a local NTP server

Clocks

There are two type of clocks mechanisms drive systems widely available in the UK: minute alternative pulse, and half-minute pulse.

Minute alternative pulse is a simplified AC motor, extremely similar to a modern quartz movement, but runs on a much lower frequency at 1/120 Hz. Pulses at +V and -V (usually 12, 24, 60 etc.) with duration less than a second at one-minute interval are sent to the movements, and the clock turns. Clock from European manufactures (such as Mobatime, T&N etc.) majorly adopt this mechanism.

Half-minute pulse works with a latch system, used by many British manufacturer. The clock at Baker Street tube station also works with this mechanism unmodified (I presume?). A pulse at same voltage and current is sent to the clocks every 30 s to trigger the latch, and advance the minute hand for 1/120th of a turn. This is simpler in electrically as it doesn’t require alternative pulse, but it is mechanically less durable as mechanical contacts are requires. I might go about how to CNC mill a replacement latch but that’s a story later.

Code

The code is available at Github, if you can’t understand them, then please stop here and visit the vintage dealers.

Circuits

I will provide more detail to this later, as I am currently working on a continuing project with a half-minute pulse clock running on a lower voltage.

Future work?

It worked, it works, and it will work. Not much future work is required right now for the drive, apart from the occasional network glitch that ruins the timekeeping. However, I need to fix the coil on a movement and rubber gear on another so they can be connected up to the current driving system.