// the find
rbaron/b-parasite
🌱💧 An open source DIY soil moisture sensor
b-parasite is a DIY capacitive soil moisture sensor built around nRF52840/nRF52833, broadcasting readings over BLE using the BTHome protocol for direct Home Assistant integration. It measures soil moisture, air temperature/humidity, and ambient light from a CR2032 coin cell rated for 2+ years. This is for someone who wants to solder their own PCB and actually understands what they're building.
BTHome support is the right call — no custom integration to maintain, just pairs directly with Home Assistant's BLE scanner. The nRF52 choice is solid: deep sleep current in the low microamp range makes the 2-year battery claim plausible, and there's real power profile data in the repo to back it up rather than just marketing numbers. KiCad source files, gerbers, and a calibration dataset are all included, so you can order boards from JLCPCB without reverse-engineering anything. The ESPHome BLE-MQTT bridge is a nice escape hatch if your HA instance isn't close enough to pick up the BLE advertisements directly.
Zigbee support is explicitly labeled experimental and the README warns it's 'educational/exploratory' — don't plan a production deployment around it. Calibration is per-soil-type and the included dry/wet CSV data is a starting point, not a substitute for calibrating in your actual soil; you'll get wildly different readings in peat vs. potting mix vs. clay without doing it yourself. The nRF Connect SDK / Zephyr build toolchain is a genuine pain to set up locally — the Docker build script exists but west workspace management has enough sharp edges that first-timers will lose an afternoon. No OTA firmware update path means physically retrieving sensors from plant pots whenever you want to update firmware.