12 months of continuous physiological monitoring from a CR2450 coin cell, with BLE connectivity and weeks of onboard data storage.
The Solution
Built around the nRF52832 with a PCB trace antenna (saves cost and board space at the expense of tighter impedance matching and ground plane tuning). Aggressive duty cycling: IMU wakes MCU on motion events, sensor sampling adapts based on activity level, BLE advertising intervals stretch during inactive periods. 64Mbit SPI flash for data logging between sync sessions.
Results
Hit 14 months in accelerated discharge testing. The PCB antenna gets -68dBm at 3m, more than adequate for a wearable-to-phone link.
How a Coin Cell Budget Like This Works
Architecture. The radio, the motion wake-up and the logging all hang off one SoC, so everything except a motion interrupt can stay asleep.Where the average current goes at a 1 second advertising interval. Advertising alone outweighs every always-on block combined, which is why the advertising interval stretches whenever the wearer is inactive.
Estimated battery life against advertising interval, for the baseline above on a CR2450 derated to 80% of its 620 mAh rating. Stretching the interval pays off up to a few seconds, then the always-on blocks set the limit. This baseline leaves out sensor sampling, logging and sync sessions, which in a real wearable take most of the energy and bring the life down to months.Show the numbers
