
JRWatch, a Low-Power BLE Smartwatch
A 36 mm nRF52840 smartwatch board that sleeps at about 15 µA, designed entirely in code.
- Problem
- Most smartwatches last a few days on a charge because low power is an afterthought. I wanted a watch that runs for months on a 150 mAh cell, with every current number justified before ordering the board.
- What I built
- A 4-layer 36 x 36 mm board with an nRF52840, an nPM1300 PMIC with two switched power domains and a 370 nA ship mode, a BMI270 IMU for motion wake, and a Sharp memory-in-pixel display that holds a static watch face at about 4 µA. The schematic is written in SKiDL, placement and routing are scripted through the pcbnew API, and the Zephyr firmware builds in CI with a custom board definition. The OpenSCAD case is dimensioned from the board file.
- Outcome
- ERC and DRC are clean. The firmware fits in 231 KiB of flash and 40 KiB of RAM. The power budget works out to 4 to 8 months per charge, with each line cited in the verification report. Next step is confirming the numbers with a PPK2 at bring-up.
nRF52840 · Zephyr RTOS · SKiDL · KiCad · nPM1300 · BMI270 · C · OpenSCAD
GitHub
