remote code learning

[dhouston]

Bruce,

Many of the IR protocols go back 40 years or more when both remotes and receivers were less refined. The overall length of the code is not as important as the bit times. For both PPM (e.g. NEC) and PWM (e.g. Sony) the difference between a 1-bit and 0-bit depends solely on the time between rising edges and the duration of a 1-bit is usually twice the duration of a 0-bit so differentiating them is very easy. The NEC protocol is detailed in the datasheet for their µPD6121.

I haven't tested every protocol but have tested several using either a Pronto or a device I designed a few years back (when early PDAs had a CF slot) that sent IR codes. I found the receivers were very tolerant. I've done similar tests with various RF devices (X10, ceiling fans, garage door openers, etc.) with similar results. And, while not much of a factor for this discussion, most consumer IR receivers also have a fairly wide bandwidth (±5kHz) and this does come into play as many protocols are defined using cycles of carrier rather than time.

Even biphase protocols like Philips RC5, etc. are forgiving as their timing is contained within the code..

That said, when designing transmitters, I tried to keep them within ±10%.