A coin-cell-powered wireless environmental sensor case study — ultra-low-power MCU/radio and sensor selection, a fully worked battery-life calculation, low-power firmware architecture, and RF-aware PCB layout for a multi-year field deployment.
The project brief: a facility needs temperature, humidity, and motion awareness in dozens of locations with no nearby AC power and no appetite for frequent battery changes, so this board runs entirely on a single CR2032 coin cell while reporting readings over a low-power BLE link. Hitting a multi-year battery life target is not a firmware afterthought — it is a whole-system power budget that starts with MCU and radio selection and runs through every sensor, every PCB layout decision, and every line of sleep/wake firmware logic.
This module walks the whole design the way a real low-power embedded engineer would: why sleep current, not active current, is the spec that actually decides battery life, a fully worked calculation combining sleep and active charge into one duty-cycled average current and dividing it into a realistically derated battery capacity, an event-driven firmware architecture built around interrupt wake sources instead of polling, and the RF-aware layout that keeps a noisy digital sensor bus from wrecking the antenna’s performance. The full worked numbers, complete bill of materials, and finished design reasoning are part of the unlocked module below.