Firmware for a LiFePO4 12V battery monitor with automatic capacity calibration. Voltage range auto-calibrates from actual battery readings.
- Auto capacity calibration using exponential doubling: estimates converge with each discharge/rest cycle
- SOC estimation from voltage lookup + coulomb counting + rest blending
- INA226 current auto-zero eliminates offset drift
- Eco mode (deep sleep) with adaptive wake interval
- OLED display with SOC gauge, voltage, current, power, time remaining
- Configurable cell count (1-16S), nominal capacity, eco mode
- Calibration simulation tool for parameter validation
The system measures energy consumed (coulombs) between two rest voltage readings. It starts with a 2-minute segment and doubles the target each time. Each estimate is weighted by its delta SOC — large segments have more influence. The capacity starts at the nominal value and converges continuously.
A segment is invalidated if sustained charging (>1A for >10s) is detected. Brief current spikes from load cycling (compressor, etc.) are tolerated.
At rest (current < 0.3A for 5s), the SOC blends 8% toward the voltage-based estimate. This corrects coulomb counting drift while avoiding jumps on the flat LFP voltage curve.
Vmin and Vmax converge toward observed rest voltages. This adapts the SOC curve to the actual battery without changing the LFP curve shape.
Requires PlatformIO.
# Prototype (Arduino Nano)
pio run -e nano -t upload
# Production (ATmega328PB + USBasp)
pio run -e prod -t upload| Action | Effect |
|---|---|
| Hold center 0.5s | Open settings menu |
| Hold center 3s | Enter deep sleep |
| Hold any button at boot 5s | Keypad calibration |
| UP/DOWN in menu | Navigate / change value |
| CENTER in menu | Enter edit / save |
| LEFT in menu | Cancel edit / go back |
MIT — see LICENSE.txt