The project is still very much in the design phase, and I can't publish any code yet until I've gone through the copyright release process with my employer (this is a purely personal project, and is not associated in any way with my employer).

This project took inspiration from these projects:

• Chronio
• Samson March's Smartwatch

Motivation

I've never wanted a smartwatch, because I never really saw the value proposition. I've worn a Casio G-Shock since I was 11. It's durable, solar-powered, and atomic-set. I'm only on my second one because the first one's rubberized casing started to fail; the watch itself was fine.

Nevertheless, that hasn't stopped me from wanting to design and build one. I consider myself a proficient programmer and competent at designing simple PCBs, but I've never done anything that required low power consumption, nor anything that needed to fit in a space as small as a wristwatch, nor anything with a battery. So this should be fun.

Inspiration

I'm basing this project around a few different points of inspiration. In addition to the two projects linked above, I've been recently fascinated by the power consumption numbers of Sharp Memory LCDs. A display that's always-on and requires tens of microamps to sustain yet requires no complex driver circuitry seems like the perfect blend between e-ink and LCD technology.

Then I came across the nRF52840, which claims a 1.5uA sleep current with RTC wakeups and RAM retention enabled, and an average of ~30uA in BLE advertising mode. I'm sure this is neither the lowest consumption available nor the first to promise these numbers, but coming from the world of the ESP8266 / ESP32, this was staggering. Combined with Memory LCD, it suddenly seemed like wrist-mounted technology was within reach. After all, a 500mAh battery will fit comfortably in a device the size of a typical smartwatch. Even if I assume 500uA average power draw for the system, that's 41 days of life. 

This got me thinking. If I had a completely programmable, BLE-enabled device on my wrist at all times, what would I do? If I paired it with my phone, suddenly that BLE radio can call webhooks into my home automation system. I could pair it with my laptop using an HID profile, and use it as a remote when giving presentations. And I've always believed that watches should have flashlights in them; now I finally had a chance to make that happen.