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README
π Dormouse
A tiny, coin-cell Zigbee climate sensor that hibernates like its namesake β years on a CR2032, and joins Home Assistant with zero cloud.
What it is
Dormouse is a from-scratch, open-hardware temperature + humidity sensor on the
Silicon Labs MGM210LA22JNF2 module (EFR32MG21, Cortex-M33, 2.4 GHz). It's a Zigbee
sleepy end device: it wakes every 5 minutes, reads an external Sensirion SHT40
over IΒ²C, reports temperature, relative humidity and battery level over Zigbee, then
drops back to EM2 sleep. On a single CR2032 that budgets out to multi-year
battery life. No hub beyond your existing Zigbee coordinator, no cloud, no vendor lock-in.
Why "Dormouse"? A dormouse hibernates and briefly stirs to feed β which is
exactly what a Zigbee sleepy end device does: sleep deep in EM2, wake for a few
milliseconds every five minutes, report, and doze off again.
Everything is here: firmware, a ,
a , the , and the
.
π Coin-cell native β sleepy end device, EM2 sleep, TX power capped so a CR2032 never browns out. ~1β3 Β΅A average.
π‘οΈ Real ambient temp + humidity β external SHT40 (Β±0.2 Β°C / Β±1.8 %RH), CRC-checked, one-shot read per wake.
π Zero-config Home Assistant β temperature, humidity and battery auto-expose over ZHA; a ready-made Zigbee2MQTT converter is included.
π Runtime debug mode β flip a switch in HA to drop to 10 s sampling and stream a live log line, over a manufacturer-specific Zigbee cluster. Auto-off on boot so it never drains the cell.
π‘οΈ Self-healing β software watchdog (spans the multi-minute sleep), IΒ²C bus recovery, and a button-less factory reset (power-cycle 5Γ quickly β re-commission).
βββββββββββββββββββββββββββββ every 5 min (10 s in debug) βββββββββββββββββββββββββββββ
β β
wake ββ€ SHT40 read (IΒ²C, CRC) β IADC battery read β write ZCL attrs β reporting β EM2 sleep
β temp + RH VDD via AVDD/4 temp/RH/batt pushes to
β coordinator
ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
ZCL model (endpoint 1, HA Temperature Sensor 0x0302):
Basic Β· Power Config Β· Identify Β· Temperature (0x0402) Β· Humidity (0x0405) Β· MGM Debug (0xFC10)
The .slcp manifest is the source of truth for components, the target part,
sleepy-device timing and TX power. The ZCL data model lives in a ZAP file; the
#defines in src/app.h mirror it. See CLAUDE.md for the full
architecture write-up.
π§ Hardware
Tiny 2-layer, ~36 Γ 25 mm board. The MGM210L sits at the top edge with its
integrated antenna pointing off-board and a copper keepout around it; the
CR2032 holder is on the back; the SHT40 is at the bottom edge for airflow.
Full wiring, pinout and CR2032 power design: docs/hardware.md.
KiCad sources, custom libraries and PCB notes: hardware/README.md.
Manufacturing files (Gerbers, drill, BOM, pick-and-place): hardware/fab/.
π Build & flash
There is no host/unit-test suite β this is on-target firmware. "Testing" means
flashing and watching the join + reports over RTT and in ZHA/Z2M. The toolchain is
installed via SLT (Silicon Labs Tool).
Then put your Zigbee network in join mode (ZHA: Add device; Z2M: permit_join)
and power the sensor. Verified working with SDK 2026.6.0, slc-cli 6.0.22, GCC 14.2.
π Home Assistant
ZHA β temperature, humidity and battery are zero-config (standard clusters).
The custom debug cluster needs a small ZHA quirk to expose.
Zigbee2MQTT β drop integration/zigbee2mqtt/dormouse.js
in as an external converter. It exposes temperature, humidity, battery, and the
debug entities (debug_mode switch, debug_log, debug_status, sample_interval).
ποΈ Repository layout
Path
What
mgm210l_zigbee_temp.slcp
Project manifest β components, target, config. Source of truth.
Nudge the one SDA trace to clear the cosmetic 0.05 mm edge-clearance DRC note
π€ Contributing
Issues and PRs welcome β especially hardware bring-up reports, battery-life data,
and the "help wanted" items above. Please read CLAUDE.md first; it
explains the two-stage build, the .slcp-is-truth rule, and the ZCL/app.h/converter
sync requirement that's easy to trip over.
π License
MIT β see LICENSE. Firmware builds against the Silicon Labs Simplicity
SDK, which carries its own (permissive) license; it is not vendored here β the
build fetches it via SLT.
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