IR Remote Encoding Algorithm

[last updated: 2025-01-17]
IR Remote - home page
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This page is in process ...

• The IR signal sent out by your IR sender is a series of pulses of a 38 KHz carrier wave (usually 38KHz, but not always).
  The pulses vary in length, very roughly on the order of 500 - 2000 microseconds.
• Different device manufacturers (Sony, NEC, etc.) use different data protocols ("encoding algorithms") for the signals sent from their IR remotes.
  Main differences between protocols from different manufacturers:
  • total number of data bits used to encode a given key press
  • number and length of pulses to define the "starting sequence"
  • more complicated configuration patterns, eg. how many data sets sent per button press,
    whether inverted data is sent,
    whether bits (1's & 0's) are correlated to simple pulse length or to more complicated patterns,
    presence of "toggle" bits to discriminate between multiple button presses vs. a held-down button
• Pressing different buttons on your remote will always send out a 38 KHz pulse train.
  The pulse train is composed of some number of pulses of different lengths.
  A given button-press is identified by the unique pattern of pulses and their lengths.
  Measuring the number and lengths of the received pulses is therefore necessary to differentiate between different button-presses.
• The pulse train that is sent when you press a button on the remote
  often consists of a "start sequence" followed by data.
  The entire pulse train, start + data, may be sent 2 or 3 times, to guarantee accurate reception, depending on the device and manufacturer.
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• So Far, So Good ...
  • The above is the total of the general information that I'm pretty sure of.
  • If you want to "look at" and deeply investigate the encoding algorithm of a pulse train,
    you have to look at the "raw data" that is put out when you press a button on the remote.
        See "Getting Raw Data" section here.
  • I have found 3 Arduino methods to do that:
    the Adafruit method, which uses clever programming without added libraries,
    using the IRLib2 library,
    and using the IRremote library
  • My problem is, I have not been able to reconcile the two of those methods that both give "raw data."
    That is, the data they output are different from each other.

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• So where to go from here?
  • One could dig deeper into the protocol and format of the raw data,
    and presumably, hopefully, eventually, come to an understanding and explanation of
    precisely how the signals are encoded.
  • Or, one could just wave their hands at the mystery,
    and proceed to use the libraries to do the heavy lifting,
    and just make a project that works.
  • That's what I'm going to do at this time.
    I may come back to it at some later date, but ... later.

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• ... proceed to decode the raw data ...
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eof