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Battery_Setup is an OpenBeken command that tells a BK7231N-based, battery-powered device how to translate the raw ADC reading on the BAT_ADC pin into a real battery voltage and a “battery-percentage” value. Battery_Setup <vmin_mV> <vmax_mV> [vdivider] [vref_mV] [adcbits]Key points
• vmin_mV – voltage at which the pack is considered empty
• vmax_mV – voltage at which the pack is considered full
• vdivider – ratio of the external resistor divider (default ≈ 2.29)
• vref_mV – ADC reference (BK72xx is fixed ≈ 2400 mV but kept for future chips)
• adcbits – ADC resolution (BK7231N: 4096 counts for 12-bit)
The command is recognised only when at least one GPIO is declared as BAT_ADC.
adc_raw.\[ V{ADC}= \frac{adc_raw}{2^{adcbits}-1}\times V{ref} \]
• Pack voltage
\[ V{BAT}=V{ADC}\times vdivider \]
• Percentage
\[ \%\;=\;\text{clamp}!\left(\frac{V{BAT}-v{min}}{v{max}-v{min}}\times100,\,0,\,100\right) \]
The values are advertised via MQTT/Home Assistant in the sensor.battery entity.
Typical hardware
• A high-value divider (≥ 1 MΩ top resistor) limits sleep current to ≈ 3 µA.
• For ultra-low-power designs add a P-MOSFET or NPN to switch the divider on only during measurement.
Measurement cadence
• Battery_cycle <N> sets the period; default 10 s (= 10 OpenBeken frames).
• On deep-sleep devices you usually disable the periodic task and call Battery_MeasureNow in your wake-up script, saving tens of µA.
Example calibrations
• 2 × AAA Alkaline door sensor
setPinRole 24 BAT_ADC ;GPIO24 wired to divider
Battery_Setup 2000 3100 3.09 ;empty @2.0 V, full @3.1 V, divider 1 M/470 k
Battery_cycle 120 ;measure every 2 min• 1-cell Li-Po with 1 MΩ/330 kΩ divider
Battery_Setup 3000 4200 4.03• Lithium-thionyl (ER14250) 3 V primary
Battery_Setup 2500 3400 2.29• The argument order (vmin vmax …) was unified across OpenBeken builds in Q4-2023; older tutorials show the legacy order.
• Deep-sleep patches (Oct-2023 → Jan-2024) reduced BK7231N sleep current to ≈ 7.5 µA when Wi-Fi/RTC are off, extending coin-cell life to > 1 year in sensor workloads.
• Home Assistant’s MQTT auto-discovery template now recognises the battery device-class automatically when the BAT_ADC role is present.
Voltage-divider design
• Divider ratio
\[ vdivider = 1+\frac{R{top}}{R{bottom}} \]
• Choose R_top ≥ 1 MΩ to keep divider current < 3 µA.
• Measure the exact ratio with a lab DMM; component tolerances easily introduce 2–3 % error, which becomes visible near the low-battery threshold.
Impact on battery life
• A permanent divider of 3 µA drains ≈ 26 mAh/month – acceptable for 2400 mAh AA cells but unacceptable for CR2032 (230 mAh). Use a switched divider there.
• For rechargeable Li-ion/Li-Po cells incorporate proper charge/protection ICs (TP4056, DW01) to meet IEC 62133 and UN 38.3 transport rules.
• Accurate low-battery signalling avoids deep-discharging primary cells, preventing leakage and environmental harm.
Implementation checklist
Battery_Setup with measured parameters. vdivider. Typical challenges & mitigations
• ADC noise → add 100 nF from ADC pin to GND.
• Wrong percentage curve → mis-ordered parameters; confirm with Battery_Show.
• Unexpected drain → divider not switched; confirm with a µA-meter in sleep.
• BK7231N ADC absolute accuracy is ±2 %, so reported SoC is an estimate, not a coulomb count.
• Temperature dependence of alkaline cells can falsify low-battery reporting; compensate in firmware if used outdoors.
• Evaluate integrating a fuel-gauge IC (e.g. MAX17048) for Li-Po packs where precise SoC is needed.
• Study the new BK7236 chip — expected to bring an on-chip LDO with nA-range Iq which may simplify future battery sensors.
• Investigate buck regulators such as TI TPS62840 (Iq = 60 nA) when the product spends > 5 % of the time in Wi-Fi Tx.
Battery_Setup calibrates how OpenBeken running on a BK7231N converts ADC readings into a true battery voltage and percentage. Provide vmin, vmax, and the exact resistor-divider ratio; verify with a meter; tune sampling frequency for the best compromise between accuracy and power. Correct calibration, together with deep-sleep firmware and low-leakage hardware, is the cornerstone of year-long battery life in BK7231N IoT sensors.