An Electronic Candle You Light with Fire and Blow Out

The Skeuomorphicer Candle turns on when heated by a flame and turns off when you blow on it. A thermistor responds to the heat and switches the circuit on. Once lit, warmth from nearby resistors keeps it on; a puff of air cools the circuit and turns it off.

Maker Marek designed it without a microcontroller, using a single transistor, a thermistor and a handful of passive components. Keeping the thermal feedback reliable required careful tuning, and battery voltage can affect its behavior.