The Future of Wristwatches?

Traditional wristwatches are seen on wrists less frequently these days. Most people opt to use their phones to check the time, and those that still want to wear a watch tend to lean towards smartwatches. From the standpoint of practicality, this makes a lot of sense. Why have an entire device dedicated to nothing more than telling the time in this day and age?

But watches are not only about function — they can also be an important part of one’s personal style. For hardware hacker Sahko, that style happens to be pretty unusual, so he decided to make his own wristwatch. On the surface, his watch may just tell the time, but it also screams, “I just arrived in this quaint era from the distant future.” No phone or commercial smartwatch on the market is going to give off those vibes.

The inspiration for the entire project is the HCMS2901 amber LED dot-matrix display module. After breadboarding a prototype with a Raspberry Pi Pico, Sahko started working on the final hardware design. The idea was to have the display modules cover the entire length of the wristband, so he decided to just make the wristband from a flexible PCB, which greatly simplified the wiring.

Since the RP2040 microcontroller package used by the Pico is on the large side, and it also requires external flash memory and an oscillator, Sahko instead settled on using the STMicroelectronics STM32U083KCU6. This all-in-one package only needs to be supplied with power, so a LiPo battery and charging circuit rounded out the design. The clasp is made from a pin header, which is also used for charging the battery.

With 14 displays, the battery would only last about two hours if they were used continuously. So a set of three buttons was added to turn on the screens and adjust the brightness level.

With all of that screen real estate, something really special needed to be done to make proper use of it. For this reason, Sahko coded a really slick, Matrix-like digital rain effect that shows on all of the screens before the current time is displayed. And anyway, random characters will obviously float all over every screen in the future.

If you want to get your hands on one of these watches, there will be a lot of obstacles standing in your way. First and foremost, the display modules cost about $30 each, which means a typical watch will cost over $400 in displays alone. Aside from that, the flexible PCB is not exactly the best material for a wristband, so solder joints fail frequently and you would be likely to spend more time repairing the watch than actually wearing it. But if that is not enough to deter you, the hardware design and source code are available on GitHub.