One is power (+5 or +3.3 usually), the other ground. The third will be
the recovered signal. Usually, it will be a low when an IR rcvr sees a
modulated stream at its base frequency (38kHz, 40KHz, etc.),and when it
is absent it output is high. But there's no guarantee without knowing
the specs of the particular device. Does it have a part number on it?
Here's a popular one you might look at for comparison
Randy M. Dumse
Caution: Objects in mirror are more confused than they appear.
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