This project is a simple heat detector built with only 5 electronic components. A thermistor senses changes in temperature, and a transistor circuit activates an active buzzer when the thermistor is exposed to sufficient heat.
How does it work ?
A thermistor is a resistor whose resistance changes with temperature. It acts as the sensor in this circuit, responding to the heat from a nearby flame.
When the thermistor becomes sufficiently hot, the change in resistance causes the transistor circuit to switch state. This activates the buzzer.
The exact temperature at which the buzzer starts sounding depends on the thermistor, the resistor values and the characteristics of the transistor.
An active buzzer contains its own oscillating circuit, so it produces a sound when the appropriate supply voltage is applied.
Electronics component Fun Kit (with breadboard & power supply module)
General purpose transistors - BC547 (NPN) & BC557 (PNP) pack
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