Electro Lab: Smoke Detector Project

A smoke detector is a device that detects the presence of smoke. It can be made by the following circuit in figure-01. An Operational amplifier comparator is used here. When light falls on the light dependent resistor (LDR)’plate, resistance decreases and resistance increases with decreasing intensity of light. Smoke detector is made by using the working principle of the LDR.

Component:
1) Micro amp -741
2) Resistor (10 kilo ohm)
3) LDR
4) LED
5) Potentiometer
6) Battery
7) Battery cap
8) Buzzer

Connection: 

Working and Design of Circuit components:
Operational amplifier can be used as comparator. Here an IC op amp voltage comparator is used. Connect the potentiometer’s middle terminal to the inverting input and the others to ground and with positive terminal of battery respectively .Connect a 10k resistor between the non- inverting input terminal and the positive terminal of battery. Connected a LDR between the ground or negative terminal of battery and non-inverting input terminal.
A led is used just for lighting. Make a cylindrical box and it’s bottom should be opened. Set a LED and a LDR on the two terminals of the cylindrical box. The LED is always switched on and light falls on the surface of LDR’s plate. When light decreases on the surface of the LDR’s plate, the resistance of the Light dependent resistor increases and when light increases resistance decreases. When smoke enters into the cylindrical box at the opened bottom surface, light decreases on the surface of LDR because smoke impedes the light flow. As a result, the resistance of the LDR increases. Operational amplifier comparator indicates the non-inverting input terminal as of high voltage. So the output will be positive.
LED permits current to flow in only one direction, so the LED turns on and buzzer will also signaling. But when smoke does not enter the LED and buzzer turns off.