Thursday, May 26, 2011

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Smoke Detector

           Small change of light the smoke detector will be activating. Initially photo-conductor resistance shall have to high value. Total Circuit designing. Smoke Detector is a detector which is activating by the smoke. It is another practical application of a voltage-level detector. Smoke Detector is working with the change of voltage. This circuit can be used in fire alarm.

          Smoke Detector of Figure the lamp and photo-conductive cell are in an enclosed chamber that admits smoke or dust but not external light. The photo-conductor is a light-sensitive resistor. In the absence of smoke or dust, very little strikes the photo-conductor and its resistance stays at some high value, typically several hundred kilohms. The 10-kΩ sensitivity control is adjusted until the alarm turns off.

          Any particles entering the chamber cause light to reflect off the particles and strike the photo-conductor. This, in turn, causes the photo-conductor resistance to decrease and the voltage across R1 to increase. As Ei increases above Vref, Vo switches from –Vsat to +Vsat, causing the alarm to sound. 
           In initial condition photoconductor resistance must contain high resistance otherwise the detector will be always activated. When the voltage of inverting terminal and non-inverting terminal are same output show 0 V. 

           Output voltages not more then supply voltage. The resistive network at the input of the op-amp forms a Wheatstone bridge. This circuit can be used to monitor the level of dust particles in a clean room.


  1. A smoke detector are undoubtedly important to have in every home. Keeping them in good shape will ensure that you and your family remain safe from fire and smoke inhalation.

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  2. Good work…unique site and interesting too… keep it up…looking forward for more updates.
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