Watch Out!

When looking for a new smartwatch, most people go shopping to find the device that best suits them. A select few skip the shopping trip and fire up KiCad to design their own hardware instead. Jonathan Rico is definitely in this latter group, having previously designed Ledwatch, he has now set his sights on building a more practical device that people would actually like to use every day. Sure, Ledwatch is a very cool build, but who really wants to wear a watch that displays the time in binary on a daily basis?

Since we all have different tastes in smartwatch features, Rico decided to build a modular smartwatch platform called M-watch around the Nordic Semiconductor nRF52840 system on a chip (SoC). A minimal system would consist of a core board, where processing and timekeeping take place, and a display board of some sort to present information to the wearer.

The current core board is built with an nRF52840 SoC with a 64MHz Arm Cortex-M4 processor, 256KB of RAM, and Bluetooth Low Energy wireless connectivity. The board also includes an accelerometer, which has many practical sensing applications, as well as a motor driver and LiPo battery charger. For the display board, Rico is starting small with a 24 RGB LED matrix and an ambient light sensor that could be used to adjust display brightness for the current lighting conditions.

Not really what you had in mind for your ideal watch? Well, that is where the fun comes in — the M-watch is modular, so you can pick and choose the types of boards you want to include for the display and other sensing functionalities. Of course this is (for now, anyway) a personal project, so you would have to design those boards yourself, but the M-watch provides a nice, clean framework in which to do so.

Rico imagines another watch option in which the sensor board contains a heart rate monitor and wireless charger, and the display board has a color LCD and NFC transceiver. Or if you are into minimalism and want the battery to last a long time, the display board might contain a segmented LCD, in which case the entire watch could be powered by a coin cell. If you can not make up your mind, you can swap out boards whenever you want by simply snapping the mezzanine connectors together and putting it back in the case.

The case itself is 3D-printed, which may look a little too DIY for some people—but if you happen to be into designing custom PCBs for a smartwatch because nothing off-the-shelf quite floats your boat, then it might be right up your alley. Rico also designed a cradle for the watch to make it easy to recharge the battery and flash the firmware without having to disassemble the device.

Is M-watch usable? In Rico's case, yes. He has been wearing his creation daily for the past two months. Will it work for you? The only way to be sure is to go grab the design files and roll your own M-watch. Go ahead, you know you want to.