Rednexing's Compact Espressif ESP32-S2 Smart Home Sensor Board Runs for Three Years on AA Batteries
Designed around the footprint of a three-battery holder, this compact board wakes itself —and connected sensors — once an hour.
UPDATE (3/4/2025): Richard Axelsson is preparing to launch a crowdfunding campaign for a commercial version of his low-power Espressif ESP32-based Internet of Things board, capable of running for three years from a triplet of AA alkaline batteries — and it's now called the PowerTortoise IoT.
"The actual run time depends on the batteries and sleep duration," Axelsson claims of the design, which was launched on Tindie late last year. "Using MQTT, one reading/hour can yield an eight-year lifespan."
The crowdfunding campaign launches soon on Crowd Supply, with interested parties invited to sign up to be notified when it goes live.
Original article continues below.
Engineer Richard Axelsson has built an Espressif ESP32-S2-based sensor board designed for a low enough power draw to run from three AA alkaline batteries for an impressive three years.
"I need to control for risk of mold in areas that are hard to access and with no power, like crawl space, attic, storage building, etc.," Axelsson explains of the idea behind the sensor system. "I wanted a board to measure temperature and humidity, but also be able to hook up other sensors and functions. I only need to measure once an hour, and sleep the rest of the time, which means this board will run for more than three years."
The compact board is designed to sit on the back of a three-battery AA holder, taking up the same footprint — delivering a device robust enough, its creator claims, that it doesn't need any kind of enclosure for indoor use. 3.3V and battery-level power outputs for external sensors, which can be connected to general-purpose input/output (GPIO) pins broken out on 0.1" headers and screw terminals, are switched on only when the board is active to cut down on power drain — though always-on outputs are also available.
A USB Type-C connector is provided for programming the Espressif ESP32-S2-MINI module, which also provides Wi-Fi connectivity, and there's an on-board Aosong ASAIR AHT10 temperature and humidity sensor — plus analog-to-digital (ADC) channels for external analog sensors. The sensor board is designed for use with the ESPHome firmware, allowing it to integrate into Home Assistant with ease — though, Rednexing warns, it does not support over-the-air (OTA) programming.
Axelsson's Rendexing is selling assembled units on Tindie at $40; schematics and sample YAML configurations are available on GitHub under an unspecified license.
