Electronics > Projects, Designs, and Technical Stuff
IR communication protocol/design for low latency/fast response - ideas?
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pwlps:

--- Quote from: Marco on May 24, 2019, 12:54:19 pm ---Now whether frequency division multiplexing is a better way to share the spectrum than time division here is debatable.

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Of course, but here we were not talking about how to optimize a standard for best spectral efficiency, the question was rather how to make a simple but robust system with a few channels, focusing on the ease and robustness of the actual implementation. TDMA will work with simpler electronics but will need a more robust software protocol (collision detection etc.), FDMA needs more analog stages but eliminates many problems too. Consider such an annex problem like the AGC training: in FDMA this is handled by the analog stage IC, but in a direct carrierless coding you don't have it and I don't even know how it is achieved, do we need to append long preambles ?
pwlps:

--- Quote from: ogden on May 24, 2019, 01:53:44 pm ---Well, then explain your phase modulation principles of IR LED light which does not allow phase (of the light) modulation.

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I don't have time to give a course on modulation now but note that there is nothing new here. Carrier modulation is used in IR remote control standards like Sony SIRC or Philips RC-5 : https://en.wikipedia.org/wiki/RC-5. In RC-5 "the command data is a Manchester coded bitstream modulating a 36 kHz carrier". As you see the carrier has nothing to do with the optical frequency. NB. In the standards I'm citing only amplitude modulation is used but there is no reason a phase modulation (BPSK, QPSK etc.) could not be used as well. Please try to understand all this before your next post.
pwlps:

--- Quote from: Buriedcode on May 24, 2019, 02:04:11 pm ---Lads, the OP hasn't returned, can we at least keep on topic.

--- End quote ---

As long as the discussion is entertaining who cares about the OP  :D
ogden:

--- Quote from: pwlps on May 24, 2019, 06:43:37 pm ---I don't have time to give a course on modulation

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Don't even try please.


--- Quote ---"the command data is a Manchester coded bitstream modulating a 36 kHz carrier". As you see the carrier has nothing to do with the optical frequency.

--- End quote ---

When you properly tell what actually is carrier - then sure. Look... I do not deny possibility of signal double-modulation, nor possibility to transmit QPSK-modulated baseband using amplitude modulation of IR light. What you propose is indeed possible to build, but it is pointless overengineering. It is already said multiple times here - pointless.


--- Quote ---NB. In the standards I'm citing only amplitude modulation is used but there is no reason a phase modulation (BPSK, QPSK etc.) could not be used as well.

--- End quote ---

IR remotes do not use amplitude modulation but OOK (on/off keying), even for "modulation of the carrier". BTW IR receivers have pathetic selectivity - if you point interfering (transmitting) 56KHz remote to 36KHz receiver, it can't decode 36KHz transmission aimed at it. That "carrier modulation" for TV IR remotes does not create parallel transmisison channels, it is just smart balance between design complexity and protection against false triggering from ambient IR noise and other kind of TV IR remotes.
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