IR sensors are composed of an IR emitter and an IR receiver.
IR emitter is simply an IR LED (Light emitting diode) which emits infrared light when supplied with a voltage. You can check this in action using a camera phone and looking into the LED. You will see a purple colored light coming out of the LED.
IR LED is connected in forward biased as shown in the figure.
IR receivers are photo diodes, that is they show more diode characteristics when more light falls on them. And because of this property IR receivers are connected in reverse biased. How this is helpful ?
Well these sensors are used with microcontrollers and microcontrollers understands voltage levels.
The voltage developed across IR receiver will change if its resistance changes (use simple voltage division rule with the current limiting resistor).
Initially the IR receiver has some resistance when connected in reverse biased due to ambient light. However when IR rays from IR emitter fall on the receiver, the receiver will show more diode like characteristic, that is its resistance will increase (reverse biased ). So voltage developed across it increases. This voltage is detected by microcontroller. Now we can use this to implement certain logic in the code.
IR emitter is simply an IR LED (Light emitting diode) which emits infrared light when supplied with a voltage. You can check this in action using a camera phone and looking into the LED. You will see a purple colored light coming out of the LED.
IR receivers are photo diodes, that is they show more diode characteristics when more light falls on them. And because of this property IR receivers are connected in reverse biased. How this is helpful ?
The voltage developed across IR receiver will change if its resistance changes (use simple voltage division rule with the current limiting resistor).
Initially the IR receiver has some resistance when connected in reverse biased due to ambient light. However when IR rays from IR emitter fall on the receiver, the receiver will show more diode like characteristic, that is its resistance will increase (reverse biased ). So voltage developed across it increases. This voltage is detected by microcontroller. Now we can use this to implement certain logic in the code.
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