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Understanding IR Remote Controls - Part 3

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We talked about the basics of IR (Part 1) and the SIRC protocol (Part 2). Now let's see how RC 5 protocol works.

RC 5

RC 5 was introduces by Philips. It uses IR pulses modulated to 36 KHz. The logic level encoding is simpler than in SIRC.

RC 5 Logic Levels
Logic '0' is represented by an IR pulse of 0.9ms and then waiting 0.9ms. Logic '1' is the complete opposite, 0.9ms waiting and then 0.9ms pulse. Therefore, both '0' and '1' have a similar 1.8ms pulse width.

As in SIRC, a command in RC 5 is also sent as a data packet. Its structure is as follows.

RC 5 Data Packet

As you can see, RC 5 has 2 start bits, which are always '1'. The address part and the command part are 5 bits and 6 bits respectively. Their function is similar to those of SIRC. The bit marked as 'T' has a special purpose. If you press the same button of the remote several times, the 'T' bit will toggle between 0 and 1. If you press and hold the button, the value of the 'T' bit will remain the same as the command repeats.

The RC 5 protocol is especially popular among inventors because it's easier to implement. Remote control systems based on the RC 5 protocol are both common and cheaper than others. If you have a basic understanding of microcontroller programming, you will note that RC 5 is easy to implement using microcontrollers, which I will be testing out soon....

I will do a post on how IR sensors work soon.

Special thanks to Vidusara newspaper, from which I gained this knowledge.
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Comments

  1. Sandeep EllawalaJanuary 11, 2011 at 5:03 PM

    Do you think that having 'T' bit would make a significant difference in application of RC5 protocol compared to the SIRC protocol? If so, in what ways?

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  2. Thimira AmaratungaJanuary 11, 2011 at 5:28 PM

    Well, using the 'T' bit, we can identify if a button was simply pressed and released or pressed and hold. So, a single button on the remote control can be assigned two different functions - one for simply pressing the button and one for pressing and holding. That effectively doubles the potential functionality of the remote.

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