Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!orstcs!guille!liud
From: liud@guille.ece.orst.edu (Dongtai Liu)
Newsgroups: sci.electronics
Subject: RE: Infrared remote controller decoding
Message-ID: <12459@orstcs.CS.ORST.EDU>
Date: 12 Sep 89 04:38:00 GMT
Sender: usenet@orstcs.CS.ORST.EDU
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References: <1209@clmqt.marquette.Mi.US> <12457@orstcs.CS.ORST.EDU>
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Reply-To: liud@guille.ECE.ORST.EDU (Dongtai Liu)
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Organization: Oregon State University, E&CE, Corvallis
Keywords: IR sensor make big difference! 

I guese the IR sensor you have used is a photo transistor instead of a
photo diode. The rise/fall time of a photo transistor is around 30-1000
us, depending on the sensitivity and load condition. Usually IR remote
controller use PCM modulation with carrier frequencies varying from
30kHz to 80 kHz square pulse trains. You mentioned you have seen sine
wave signal, that means your circuit filtered out the high frequency
components of the signal and the resulting signal lost details.

I suggest that you try a PIN photo diode. Since the sensitivity of PIN
diodes are much lower than photo transistors, an op-amp stage would be
necessary to amplify the signal.

Another way to decipher the coding is to check the data sheet of the
chip used in the controller unit. Signetics and Motorola data book
have detailed description about typical IR controllers. As I remember,
the mechanisms are similar although there are two types of modulation
scheme: PCM and FM. Good luck.