We bring forth efficient Smoke Detector, which alerts people as soon as it detects smoke anywhere in the building. The sensor assembly consists of white LED D1 and Photodiode D2, which are mounted face to face in an enclosure such that when smoke passes through this enclosure, a noticeable alarm is raised. We offer Smoke Detector in different specifications in order to meet divergent demands of the clients.
About the Circuit :

• The circuit is designed around IC1, which is wired in monostable mode. Photodiode D2 is connected in reverse bias mode. In presence of light, it has very low resistance. But, when light falling on it gets interrupted, its resistance increases to a very large value. This feature is used to trigger IC1.
• Diode D1 is used to fall light on D2. The intensity of light is controlled using preset P1. In absence of smoke, transistor T1 does not conduct and reset pin 4 of IC1 remains high. Output of IC1 at pin3 is low and transistor T2 remains in cut-off state and alarm is not raised.
• As soon as the smoke passes through the enclosure, light falling on D2 gets interrupted, transistor T1 conducts and reset pin4 goes low. As a result, IC1 gets triggered and pin3 goes high. Transistor T2 conducts and buzzer raises the alarm. At the same time LED D3 lights, which gives visual indication.
• Diodes D4, D5 are used to rectify the 12V AC signal and capacitor C3 is used as a filter capacitor.

We bring forth efficient Smoke Detector, which alerts people as soon as it detects smoke anywhere in the building. The sensor assembly consists of white LED D1 and Photodiode D2, which are mounted face to face in an enclosure such that when smoke passes through this enclosure, a noticeable alarm is raised. We offer Smoke Detector in different specifications in order to meet divergent demands of the clients.
About the Circuit :

• The circuit is designed around IC1, which is wired in monostable mode. Photodiode D2 is connected in reverse bias mode. In presence of light, it has very low resistance. But, when light falling on it gets interrupted, its resistance increases to a very large value. This feature is used to trigger IC1.
• Diode D1 is used to fall light on D2. The intensity of light is controlled using preset P1. In absence of smoke, transistor T1 does not conduct and reset pin 4 of IC1 remains high. Output of IC1 at pin3 is low and transistor T2 remains in cut-off state and alarm is not raised.
• As soon as the smoke passes through the enclosure, light falling on D2 gets interrupted, transistor T1 conducts and reset pin4 goes low. As a result, IC1 gets triggered and pin3 goes high. Transistor T2 conducts and buzzer raises the alarm. At the same time LED D3 lights, which gives visual indication.
• Diodes D4, D5 are used to rectify the 12V AC signal and capacitor C3 is used as a filter capacitor.