Hacks & Buildselectronicsthermal-feedbackdiy
This electronic candle needs a real flame to light and a breath to turn off
A thermistor and a transistor let a homemade electric candle mimic a real one. The clever part is the copper that keeps it warm until someone blows on it.
Lighting an electronic candle with an actual flame seems wonderfully excessive. But the flame supplies something this board needs, and the trick only works because the circuit keeps supplying it after the match leaves: enough heat to convince a temperature sensor to stay on. Heat lowers the resistance of an NTC thermistor, switching on a MOSFET and the bulb. The bulb’s current-limiting resistors warm up and keep the thermistor hot after the flame leaves.
The maker’s explanation puts the finishing move plainly: “Once you blow on the PCB, the heat is removed, breaking the cycle and turning off the light.” The board’s copper transfers enough heat to hold the circuit on, while remaining exposed enough for a breath to cool it.
Play the video on YouTubeThe current design uses about 0.1 watts of heater dissipation to hold the thermistor at roughly 55°C. That figure belongs to the maker’s tuned implementation; copying the schematic without its physical layout could leave a candle that refuses to extinguish.
Four board variants are available. The minimal board uses a miniature bulb and explicitly doesn’t work with LEDs; the recommended basic board includes power regulation. Someone copying the project has an actual choice to make before ordering parts.
The design leaves room for experimentation in its custom PCB, where brightness can be adjusted while maintaining flame detection. That opens a better next experiment than another animated flicker: how much can the light change before the candle forgets how to blow out?