liud@guille.ece.orst.edu (Dongtai Liu) (09/12/89)
Summary: Expires: References: <1209@clmqt.marquette.Mi.US> <12457@orstcs.CS.ORST.EDU> Sender: Reply-To: liud@guille.ECE.ORST.EDU (Dongtai Liu) Followup-To: Distribution: 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.
psfales@cbnewsc.ATT.COM (Peter Fales) (09/12/89)
In article <12459@orstcs.CS.ORST.EDU>, liud@guille.ece.orst.edu (Dongtai Liu) writes: > > 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. I can second this one. When I was experimenting with IR receivers I found that "typical" bipolar phototransistors and photodiodes (i.e. from Radio Shack) were both too slow for this application. PIN diodes worked fine however. There is chip made by Motorola, the MC3373, that is designed to connect directly to a PIN photodiode and provide all the necessary buffering and amplification. I have never used it, but from looking at app. notes, it should be very easy to use. I believe it is sold by other manufacturers as the 1373. -- Peter Fales AT&T, Room 5B-420 2000 N. Naperville Rd. UUCP: ...att!peter.fales Naperville, IL 60566 Domain: peter.fales@att.com work: (312) 979-8031