Here is a small & easy to make project to learn how IR transmission works.
Things you need to know:
(1). IR(Infra red) : Like light rays IR is also a type of ray. But since it has longer wavelength than visible light, we can't see them with our eyes. It has many applications like thermal Imaging, IR communication etc.
(2). Photodiode : A photodiode is like a simple diode, but the main difference is that the reverse resistance of a photodiode changes with respect to intensity of light falling on it. Thus we can say that resistance of a photodiode in reverse bias depende on the light falling on it. But the characteristic of a photodiode which I have used in this circuit is that photodiode's resistance also changes when IR(Infra red) rays fall on it. Thus I have used photodiode as a detector to detect IR rays in this project.
(3). IR LED : It is same as a simple LED but it emits IR rays rather than light. The intensity of IR rays depend on the voltage applied to it.
Circuit diagram1. Transmitter
2. Receiver
3. Transmission Medium
1. Transmitter : In this project I have used a simple IR LED to transmit IR rays. I have given input signal(It can be any type of electrical signal. I used sine wave of 5v amplitude) to battery and then to IR LED. Thus IR LED will emit IR rays whose frequency is same as frequency of input signal & its intensity depends on amplitude of the input signal.
2. Receiver : As I have mentioned above, a photodiode's resistance changes when IR rays fall on it. Thus we can use photodiode as a IR detector. I have applied reverse biasing to photodiode & connected a 500 ohm resistor. Now when IR rays fall on photodiode, its resistance changes,depending on the intensity of IR rays falling on it. So the current through the 500 ohm resistor changes. Thus this circuit acts as a IR detector.
3. Transmission Medium : It is clear that this circuit uses IR rays as a transmission medium.
Now when the receiver is given any sort of electric signal & IR LED is placed in front of photodiode the same signal as applied to receiver is produced accross the 500 ohm resistor. We can see the output with the help of a C.R.O.
I have tried this circuit & as you can see in the video , as soon as I place the photodiode in front of the IR LED we get the output(sine wave,which is input on transmitter side) same as the input as seen on C.R.O.
