Visible Light Communication in a Sevem-Segment Synchronar 2100 7s021 module

 

The Synchronar 2100, introduced in 1972 by Roger W. Riehl, was one of the pioneering solar-powered LED wristwatches. Its solar cells collected light to recharge the watch’s internal batteries, allowing the sealed watch to operate without a conventional charging connector.

 

In our modern Synchronar module 7s021, we use that same solar cell for a second purpose — communication.

 

A phone screen flashes encoded light onto the solar cell using Visible Light Communication (VLC). The watch can receive time, date, time-zone and calibration data directly through light. We originally considered Bluetooth and Wi-Fi, but both would require additional components, PCB space, power and an antenna.

 

Inside the very limited space of a vintage Synchronar case, there simply wasn’t room. The solution was already built into the watch: the solar cell.

 

Inspired by 1970s solar technology — now also the programming interface.