Stanley.......It it not particularly effective to do IR communications with an 8051 UART. A UART modulates with simple high/low levels that stay valid the whole bit cell. IR signals of the type typically received by the types of receiver that you have shown in the huge picture are modulated with a carrier frequency. Typical carrier frequencies used in the remote controls business are 36 KHz, 38 KHz and 40 KHz. The carrier is keyed on and off to represent the highs and lows of the transmitted envelop of the signal. The typical IR receiver module has an internal decoder circuit that responds to the carrier frequency and strips it out of the IR signal from the transmitter and outputs just the envelope signal. The decoder circuits used in the receivers have a nasty habbit if distorting the leading and trailing edges of the envelope signal in several ways. One way is that the leading into carrier response time is different from from the trailing out from carrier response time. The response time will also very depending how long the carrier has been present or absent. I mean that fast cell times will respond with different delay times through the part than slow cell times. Ambient light level will also affect the resonse times of the IR receiver including injecting line frequency characteristics that are most apparent from flourescent lighting.

Most IR remote protocols that are used have been carefully designed to make them workable despite the factors I have talked about. There are other factors too such as IR bounce (reflections), range from transmitter, and type of filtering lens put in front of the receiver. For example, Philips has a protocol called RC5 that is a biphase encoding (manchester) in the envelope signal such that the cell times within the message are controlled within a restricted 1x -> 2x time per/cell. With a good robust decoding scheme this biphase output from the receiver can be "self clocking" to a degree. There are other types of protocols used too including the SONY, NEC, and RECS80 formats.

About 12 years ago I experimented with a scheme to use a UART with a IR transmitter and a receiver module. I implemented it by using the UART transmit pin combining the UART output with the 16X baud rate clock through an AND gate to produce the on/off gated carrier signal to the IR LED driver. I used a baud rate of 2400 baud and thus the carrier was 38.4KHz. Using an IR receiver with a 38KHz type decoder I was able to recover the 2400 baud signal at the output of the IR receiver. Upon feeding this signal back into the UART receive pin at the destination end I was able to receive correctly part of the time. Characters with bit patterns with codes of 0xAA and 0x55 would work way better than codes like 0x81 or 0x7E. All in all the error rates under indoor conditions with flourescent lights and sending about 10 meters I was able to manage about 80 -> 85 % of characters getting through correctly. I deemed this unusable so I lowered the baud rate to 1200 baud and the modulation was now at 32X baud rate for still the same 38.4 KHz carrier. This lowered the transmission error rate to about 2%.
At 600 baud I was able to achieve an error rate of less than 0.5%. After all the experimentation I abandoned the idea of IR comm using the UART and went to an RF system for that project.

I have found that there is a significant difference in quality of product and functional performance if IR receivers from various vendors. (Not to be mean to the vendors .. but Sharp and Everlite brands were the worst products). I found the IR receivers from what used to be TEMIC to be the best of all brands. TEMIC now is the VISHAY brand and you can get data sheets at this link: http://www.vishay.com/ir-receiver-modules/

If you were to do a simple Google search using terms such as IR PROTOCOL, IR REMOTE, RC5, RECS80 you can gain a bunch more info on IR transmission.

Michael Karas