eirikr said:
1. What are the advantage and disadvantage of using 38kHz? 56kHz?
I don't think it matters which you use, the usual frequencies are around 38KHz, 56KHz is just an alternative.
I've always assumed the IR modulation frequency (38-40KHz) was chosen because it was already in use for driving ultrasonic remote controls - so they simply changed the transducers from ultrasonic to IR, and carried on using the same chips.
56KHz isn't commonly used, presumably it was added so you could have two systems working at the same time without causing too much interference. The old B&O TV's actually used a 100KHz carrier, which is why old OFA remotes wouldn't work on them.
3. What factors determine the transmission speed between two PICs communicating via IR serial signal? The clock speed of the crystal? Does higher MHz crystal means higher transmission speed can be achieved?
The clock speed doesn't matter, you can do very high serial speeds with a 4MHz clock - the main limit is the reliability of the transmission medium, the higher the data rate, the lower the reliability.
4. For my experiement, I want to send a single ASCII character (N-7-1)from one PIC via IR to another PIC. The second PIC will then send the received character to a PC via RS232 and then echo the character back to the first PIC as acknowledgement and pause the transmission for a couple seconds. The encoding scheme is similiar to SONY's SIRC: 1-bit is 1.2ms, 0-bit is 0.6ms, a 0.6ms space between pulse and a 2.4ms header. I'd like to experiement with different transmission speed, but I am not sure how to calculate the transmission speed. I am using a 12F629 with a 4MHz ceremic resonator.
There should be no problem with doing that, the SIRC system is simple and reliable.
5. How do I increase the reliability of this transmission while maintaining a high speed transmission rate?
Any scheme to increase reliability is going to reduce data rate, simply because you are sending more redundant data. As you have a two way path, you can send acknowledgements, and requests to resend, but it all slows things down.
6. If I want to achieve the highest possible transmission speed, should I use a FIR irDA transceiver like those here? (
https://www.vishay.com/ir-transceivers/)
I was under the impression that the range of these was very low (which allows a high data rate - short range, strong reliable signal path).
What are you trying to do?.