Electronics > Projects, Designs, and Technical Stuff
IR communication protocol/design for low latency/fast response - ideas?
pwlps:
--- Quote from: ogden on May 14, 2019, 02:56:33 pm ---IRDA association did not pick phase modulation but PPM instead for a good reason.
--- End quote ---
No, you still don't get it. I give up.
grifftech:
visable light, 1 wavelength per pair
ogden:
--- Quote from: pwlps on May 14, 2019, 03:20:58 pm ---
--- Quote from: ogden on May 14, 2019, 02:56:33 pm ---IRDA association did not pick phase modulation but PPM instead for a good reason.
--- End quote ---
No, you still don't get it. I give up.
--- End quote ---
No. *You** don't get it - that it is pointless to double-modulate signal.
pwlps:
--- Quote from: ogden on May 23, 2019, 04:17:28 pm ---No. *You** don't get it - that it is pointless to double-modulate signal.
--- End quote ---
I get it perfectly. It might be pointless for a single channel but the OP precised it has to handle independent communication channels. Buriedcode suggested using different carriers and I tried to develop the idea.
Here is the (basic) point you don't get yet. The direct OOK modulation such as used in IrDA (with various coding schemes, NRZ etc.) has a broad spectrum(fundamental defined by the bitrate+harmonics +possibly some subharmonics depending on the coding scheme) and it is not possible to define isolated channels by just using different modulation frequencies. The purpose of double modulation (carrier) is merely to shift the entire spectrum to some high frequency band, then choosing a large enough spacing between carriers you can have completely isolated channels. I hope it was clear this time.
ogden:
--- Quote from: pwlps on May 24, 2019, 08:30:03 am ---OP precised it has to handle independent communication channels.
--- End quote ---
Please be so kind and show quote where he said so.
--- Quote ---Buriedcode suggested using different carriers and I tried to develop the idea.
--- End quote ---
You did not develop idea of different carriers. Different carriers in optical communications means different wavelengths. https://en.wikipedia.org/wiki/Wavelength-division_multiplexing
--- Quote ---The purpose of double modulation (carrier) is merely to shift the entire spectrum to some high frequency band, then choosing a large enough spacing between carriers you can have completely isolated channels. I hope it was clear this time.
--- End quote ---
LOL, no. You suggest to use same carrier frequency - same wavelength of light, same type of IR LED to transmit multiple channels? :-//
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