I am Designing a project to use An IR remote and i am confused about the receiver. I noticed some have two legs such as this
And others have 3 legs as seen in this one
Can someone tell me the difference?
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The Ebay one is an IR Photodiode, a diode that is sensitive to IR input.
A photodiode is a semiconductor device that converts light into current. The current is generated when photons are absorbed in the photodiode.
The Sparkfun one is an IR Receiver, for Modulated IR. It takes a modulated IR signal, and strips the modulation, passing any digital signal inside to another IC. Typically used in Remote Control setups. The wiki page for the RC-5 Remote Control protocol provides a good explanation of how an IR Receiver works.
An Photodiode is a dumb analog part. A IR Receiver is a digital part (though it may have analog circuits inside).
For a remote code receiver, you need a IR Receiver. It requires a modulated signal in order to tell the difference between an intentional signal like a remote, and noise from lights in the room.
Your 'this' and 'one' link are both to standard 3-legged IR receiver modules, the ebay link is (most probably, you never know on ebay) an IR LED (tranmitter).
Now that you edited the question: your 'one' is a standard 3-leg receiver, 'this' is most likely an IR emitter LED (but it could be an IR receiver diode, which is not what you want to receive a remote control signal).