IR flame sensor module (LM393)
IR flame sensor module (VCC, GND, DO, AO) pinout, active-LOW digital output, how far it sees a flame, why sunlight triggers it, and 3.3 V wiring.
Community draft — report a mistake
3.3 V or 5 V? Outputs follow the supply, so power the module from 3.3 V on ESP32 and Pico and from 5 V on Uno. Then DO and AO are always safe for your board.
The module uses an IR photodiode (black LED-like part) sensitive to 760–1100 nm, the infrared that flames emit, and an LM393 comparator with a blue pot to set the trip level. It’s used in fire-fighting robots, stove-left-on reminders and student fire-alarm projects.
The digital output goes LOW when IR crosses the threshold; the analog output (on 4-pin versions) gives a rough strength so you can steer a robot towards the flame. Five-channel arrays exist for wider coverage.
Not a fire alarm. It only sees a flame in its direct line of sight and is easily fooled by sunlight. Use it for robots and demos, and rely on a certified smoke detector to protect people.
Prices are indicative (Nov 2026) and vary by seller.
Pinout
| Pin | What it does |
|---|---|
VCC | 3.3–5 V supply |
GND | Ground |
DO | Digital output from the comparator: LOW when a flame is detected (the DO LED lights) |
AO | Analog output — falls as IR from a flame gets stronger (4-pin modules only) |
Use it with
Common errors
Triggers in daylight or under a halogen lamp
Sunlight and incandescent bulbs are full of infrared. Shade the sensor with a short tube, point it away from windows, and raise the threshold with the pot.
Doesn’t see a candle across the room
Range is roughly 20 cm for a candle and up to about 1 m for a lighter flame, within a ±30° cone. Move it closer or use several sensors.
Logic seems reversed
DO is active-LOW: digitalRead(pin) == LOW means flame.