BMT Flame Sensor Module — Digital & Analog Output, 760nm–1100nm for Arduino & ESP32

Handy Tips

1. Two outputs for two use cases — The module provides both a digital output (DO) and an analog output (AO). Use the digital output for simple flame present/not-present triggering in alarm circuits, and the analog output when you need to measure relative flame intensity or proximity — for example to trigger different alarm levels at different distances.
2. Adjust sensitivity with the onboard trimmer — The blue potentiometer controls the LM393 comparator threshold — turning it adjusts the point at which the digital output switches from HIGH to LOW. Start with the trimmer centred, then fine-tune in your actual environment to avoid false triggers from ambient light or sunlight.
3. Sunlight and incandescent bulbs can cause false triggers — The 760nm–1100nm detection range overlaps significantly with sunlight and warm-white incandescent light output. In outdoor or brightly lit indoor environments, adjust the sensitivity trimmer to its least sensitive position and use the analog output with a software threshold rather than relying solely on the digital output.
4. Digital output logic is inverted — When a flame is detected the digital output goes LOW (0), not HIGH. Account for this in your microcontroller code by triggering your alarm on a falling edge or a LOW state rather than a HIGH — a common source of confusion when first wiring up the module.
5. Detection distance scales with flame size — The 0.8m detection distance is for a small lighter flame. A candle flame will trigger at slightly less, while a larger open flame such as a gas burner or fire can trigger the sensor from several metres away. Characterise the detection distance in your specific environment before setting alarm thresholds.
6. Mount at an angle facing downward for fire detection — For fire alarm applications, angle the sensor face slightly downward toward the expected flame source rather than mounting horizontally. This keeps the sensor face away from dust accumulation on the IR lens and improves response to floor-level ignition sources.
7. Pair with a buzzer or relay for a standalone alarm — The LM393 digital output can directly drive a small buzzer or the input of a relay module without any additional transistor or driver circuit, making it straightforward to build a completely self-contained flame alarm with just this module, a buzzer, and a 5V power supply.