Fire Alarm Circuit Schematic Diagram

This circuit will sound the speaker when smoke is detected. In normal state, the light from the bulb will be absorbed by the LDR. This thing caused the LED resistance value low. This will cause the current flow from VCC to transistor basis BD148. This high current will cause the IC COB inactive. On the other hand, if the light is blocked by smoke, IC1 and IC2 will be active and the sound will generated. The sensor sensitivity of LDR can be controlled by changing the value of VR1.

Fire Alarm Circuit Schematic

Fire Alarm Circuit Schematic Diagram

Components :
Resistor R1-R2 : 220 ohm
Resistor R3 : 2.2 ohm
VR1-VR2 : 100k ohm
Polar capacitor C1 : 470uF/25V
Polar capacitor C2 : 1000 uF/25V
Transistor : BC148
IC2 : TDA2002
Speaker : 8ohm 0.5W
9V power supply
9V light bulb

Estimated price : $20

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