Circuit Project Electronic

Here’s a cheap fire alarm circuit for building one. When there is a fire breakout in the room the temperature increases. This ultra compact and low-cost fire alarm senses fire breakout based on this fact.
Transistor BC177 (Q1) is used as the fire sensor here. When the temperature increases the leakage current of this transistor also [...]

In this fire alarm circuit, a thermistor works as the heat sensor. When temperature increases, its resistance decreases, and vice versa. At normal temperature, the resistance of the thermistor (TH1) is approximately 10 kilo-ohms, which reduces to a few ohms as the temperature increases beyond 100°C. The circuit uses readily available components and can be [...]