I have found that there are many "methods" to decode the streams of pulses that represent the data burst of an IR transmission. In looking around the WEB I have seen quite a few schemes in particular for decoding Philips RC/5 codes. I can say that many of the schemes that people have made are less robust than they could be. Here are some things I have learned that make it possible to be able to decode IR in a way to eek maximum performance out of your remote control and the detection system.

1) Use direct edge detection (interrupts are best for low overhead) as opposed to a sampled system.

2) Use a rather tight tolerance on the timing measurement of the lead in sequence of the IR burst. This may be for just the first pulse but could include two periods.

3) Once the leadin pulse is qualified try to use the widest tolerance possible to measure the pulses. If you do this carefully you can extend the detection distance for a IR control by more than 25% to 35%.

4) Always measure pulses in a non windowed or celled manner. IE, always measure from the previously qualified edge. A common RC/5 decoding scheme that I have seen some use tries to decode the RC/5 via a timed bit cell definition after the lead in pulse. This makes the the timing much more subject to decoding error than if a pulse to pulse measurement is done. This scheme can extend usable range of a remote control a considerable amount.

I can share RC/5 decoding logic, albeit not in 8051 but in TPU code, that uses a pulse to pulse scheme that has proven to be very reliable. You can either see the TPU code link in the previous posts I made or send me email to request RC/5 code specifically.

Michael Karas