This is a simple Smoke Detector circuit based on a LDR and lamp pair for sensing the fire. It uses a very simple approach to detecting smoke in the air. The alarm works by sensing the smoke produced during fire. The circuit produces an audible alarm when the fire breaks out with smoke.
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Smoke Detector Circuit Using LDR
Password : asinan
When
there is no smoke the light from the bulb will be directly falling on
the LDR.The LDR resistance will be low and so the voltage across it
(below .6V).The transistor will
be OFF and nothing happens. When there is sufficient smoke to mask the
light from falling on LDR, the LDR resistance increases and so do the
voltage across it.Now the transistor will switch to ON.This gives power
to the IC1 and it outputs 5V.This powers the tone generator IC2 to play
a music.This music will be amplified by IC3 to drive the speaker.
The diode D1 and D2 in combination drops 1.4 V to give the rated voltage (3.5V ) to UM66 .UM 66 cannot withstand more than 4V.
