Interfacing BH1750 Light with STM32 Blue Pill

BH1750 practical reference

The BH1750 is a 16-bit digital ambient light sensor that talks over I2C and returns a lux value directly — no ADC, no voltage divider, and no manual calibration curve like a raw LDR needs. Internally it uses a photodiode plus an integrating ADC and outputs a number already scaled to real-world lux.

It's the sensor to reach for whenever a project needs an actual lux measurement rather than a rough "bright vs dark" signal — automatic display brightness, greenhouse light logging, or camera exposure decisions. The catch that trips people up is the ADDR pin: leaving it floating gives unpredictable address behavior, so it should always be tied firmly to GND (address 0x23) or VCC (address 0x5C), especially useful when running two BH1750s on the same bus.

Key specifications

• Interface: I2C, up to 400kHz
• I2C address: 0x23 (ADDR to GND) or 0x5C (ADDR to VCC)
• Operating voltage: 2.4–3.6V (many breakout boards add a regulator for 5V tolerance — check yours)
• Measurement range: 1–65535 lux, direct digital output
• Resolution: 1 lux (standard mode), 0.5 lux (high-resolution mode 2)
• Measurement modes: Continuous or one-time, selectable resolution mode
• Conversion time: ~120ms (high-res mode), ~16ms (low-res mode)
• Current draw: ~120µA active, ~1µA power-down

Pinout and connection notes

Always tie ADDR to a defined level (GND or VCC) rather than leaving it floating — a floating ADDR pin can cause an unreliable or wrong I2C address at power-up.

• VCC: Power, 2.4–3.6V (check breakout for 5V tolerance)
• GND: Ground
• SCL: I2C clock
• SDA: I2C data
• ADDR: Address select — tie to GND for 0x23, or VCC for 0x5C. Never leave floating.

Integration checklist

1. Confirm the exact part number and breakout-board revision.
2. Verify supply voltage, current demand, logic levels, and signal direction against the datasheet.
3. Check controller pin assignments and bus address or interface mode against the example code.
4. Power up with external loads disconnected, then test signals before full integration.
5. If readings or communication fail, check power and ground first, then pin mapping, interface settings, and library initialization.

Troubleshooting and reproducibility

Record the board used, wiring, library/version, supply arrangement, and measured behavior. Use the selected board-specific wiring example as the source of truth. Never assume visually similar modules share identical voltage tolerance or pin order.