Infrared Transmission Decoding

Alright class, quiet down and open your books to the chapter on Manchester Encoding. [Brian J Hoskins] did just that when building this RC5 decoder. This protocol is commonly used in television remote controls. You use them on a daily basis, don’t you think it’s time you understood what’s going on? Check out his writeup and learn the dark art of invisible light communication. Or just skip the learning and follow our how-to.

[Thanks Tim]

12 thoughts on “Infrared Transmission Decoding

  1. Ir control simply is a joke. Most device makers half-ass their control (Why no discreet on/off/input codes? Why??) or they hire retarded engineers that change the IR codes for a product on every revision.

    Honestly I wish that Ir control was one of those things that was regulated and FORCED upon all manufacturer’s to not only follow a standard and include all functions in the control, but PUBLISH the codes in the user manuals.

    I’d like it to be a death penalty or at minimum any user wanting them get’s a $2500.00 fee paid to them from the manufacturer per device they own that they don’t have all control and codes in the manual.

  2. @fartface: I can see that being a problem if you lose the original remote control, but reverse engineering the protocol is usually pretty simple, at which point you can write a program to run through all of the possible commands and see what they do. Whilst I agree that it would be nice if manufacturers were more open, it doesn’t really take that long to work around the lack of information.

  3. In addition, if you *do* lose the original remote control, a pound-shop universal remote control with a code search feature can be used to identify the protocol, at which point you can work out the command codes.

  4. Nice find HaD; but check this out too…

    Dangerous Prototypes USB-IR-Toy, Links:

    BTW, I’m not affiliated in any way with Dangerous Prototypes or SeeedStudio.

    The venerable Bus Pirate is also indispensable for sniffing IR stuff.

    Regards, Drone

  5. I am impressed with this Hack’s style. It’s more impressive if viewed against the background of TV Remote history. Not all IR systems are possible to Hack on the same “hardware” either. That being due to vastly different carrier freqs and modulation schemes etc. Even weirdly strange IR ranges!

    Pre-IR “Remotes” used incredibly diverse implementations of signal transmission/coding etc. Ranging from literal hammer struck Ultrasonic “Tuning Fork” transmitter to Ultrasonic Piezos used both in the TV and Hand Unit. And one tangent of Hand Unit transmitter where a plastic bellows forced air thru “Galton Whistles” to produce Ultrasonic signals. Well, there’s a REASON for this history review. IR Carrier Freqs are often damned close to the Acoustic Ultrasonic Freqs of the past. Doing the research on those details might be a valuable learning adventure.

  6. I hope people will not mind me using this comment thread to ask a question on the topic of IR protocols.

    I am wondering if anybody knows if the standard for RC6 (and its various modes, specifically mode 6) are available anywhere one the web.

    I’d be grateful for any help.


  7. @fartface “Honestly I wish that Ir control was one of those things that was regulated”

    there used to be an acronym around here: DC-FIY (“dee see fi”)- don’t complain, fix it yourself. Seriously tho, maybe this is an area for some good open source standardization.

    I’m with you btw, I have an IR controlled lamp across the room that turns on every time my lcd monitor wakes up.

    Now for a note about the actual article: Manchester Encoding is used on magstripes too. I’ve been planning a project to do exactly this, plus decode the signal from a magswipe. Now i’m halfway done! Thanks, Brian!

  8. @fartface – IR control codes were/are regulated. Go to the NEC site or the philips RC-5 site and you will find the registered brands and their code that was assigned. The problem was there was no way to enforce the rules. RC-5 information wasn’t tightly controlled so anyone could use it.

    RC-6 changes that. You will not find published documentation on RC-6 on any manufacturer site. People have reverse engineered it and it is generally understood how it works, but it is nowhere near as public as RC-5 to prevent anyone from just using it on a device.

    Here is a library you can add to an arduino that will decode most protocols.

    Its great for learning the different protocols.

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