Some while ago, Spark Vulpes acquired several broken watches with the intention of repairing them. Some repairs were successful; some weren’t. But one in particular presented its own challenge: it had no internals. Most people would be reluctant to rip out old clockwork and put LEDs in, but as this watch was already just a case, it provided a perfect opportunity to do something different.
From the outside working in, the five rings of LEDs signify seconds, minutes, hours, and days (with Monday assigned the number 1); the final ring is used to display battery charge status. Working with such a small enclosure, and not wanting to modify it in any way, influenced many aspects of the design: most obviously the choice a 2.5 mm headphone jack to provide power, and the EFM32 Zero Gecko Cortex-M0-based chip designed for use in