If you wear a wristwatch, there are several ways to keep it accurate. Some rely on manually setting the dials, while smartwatches can interface with their smartphone “hosts” to sync things up properly. Still another technology — which has been in operation since well before smartphones — sends out a centralized RF time signal that clocks can use to set themselves. As long as you’re in range of this signal, your timepiece will never be wrong. But what if you don’t live close enough to one of these transmitters? Henner Zeller has come up with an excellent solution that doesn’t involve commuting to the proper radio zone!
Physically, Zeller’s device takes the form of a nicely 3D-printed caddy, which fixtures the watch over a Raspberry Pi Zero W with its own RF coil setup. The Pi runs a Network Time Protocol (NTP) daemon to check the time, then transmits this to the watch via RF. It’s a clever hack, and a good introduction to the Pi’s ability to transmit RF signals with only the addition of a few resistors and wire.
The system works with several different protocols, including its original German DCF77 signal, as well as UK, US, and Japanese clock synchronization signals. Besides being useful if you’re out of range of your home country’s signal, this would mean that if you prefer to wear — for instance — a German radio-synchronized watch in Japan, now you can!