Newbie Manchester Coding question
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  1. #1
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    Default Newbie Manchester Coding question

    So, I have a temperature sensor that reports in Manchester code. I need to decode it. Looking through the various examples on here leaves me confused about how to tackle this. Most of the code examples do bit conditioning/math to decode with no reliance on timing, but they all appear to rely on the assumption they're also providing the encoding process.

    eg. http://www.picbasic.co.uk/forum/showthread.php?t=198


    There's one example that decodes a 'foreign' device but that notably relies on timing as a central part of the process.

    eg. http://www.picbasic.co.uk/forum/showthread.php?t=10768

    I was under the impression that to successfully decode my device, I also need to rely on timing as there are short and long pulses of data?

    Thanks,

    Troy

  2. #2
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    Default Re: Newbie Manchester Coding question

    Usually there should be a preamble of time p in a known state, say low and then data pulses in the manchester encoding.

    Also the preamble could be a train of specific pulses, most often 50% square and then data pulses in the manchester encoding.

    Manchester encoding, since it is pulses of variable width, is based on timing also.

    So the short answer is yes. You need to measure time, then if within specs, keep the data bits and then try to decode them. Else reject the data as noise or wrong spec pulses and start over.

    Not an easy task especially if the pulses are fast (micro seconds). You may need asm routines to be quick enough and Interrupts might be one way.

    Ioannis

  3. #3
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    Default Re: Newbie Manchester Coding question

    After sending a number of pulses to the transmitter to condition the receiver data slicer you should send a high pulse of a specific length to use as a start of frame. After this pulse has completed (end of start of frame) then send the Manchester data bits and after the correct number of bits are received (2 per data bit), process the data. It is a standard practice to include a CRC of some type to validate the data stream.
    Dave Purola,
    N8NTA
    EN82fn

  4. #4
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    Default Re: Newbie Manchester Coding question

    Dave, he has already the sensor that outputs data in manchester encoding but has not said, yet, how the data are sent. Maybe RF or cable?

    Ioannis

  5. #5
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    Default Re: Newbie Manchester Coding question

    Ioannis, I use the LINX TXM-433-LR transmitter and the LINX TXM-433-LR-S receiver to send digital data (2 ports) and temperature data from my green house to the main house. I also use another transmitter for a MOLE detector in my front yard. The method has been used for ASK tire and remote keyless entry systems for vehicles for years. I have written numerous software for my former employer about 10 years ago to decode and encode ASK and FSK transmissions from the products we built for the automotive industry.
    Last edited by Dave; Yesterday at 18:43.
    Dave Purola,
    N8NTA
    EN82fn

  6. #6
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    Default Re: Newbie Manchester Coding question

    I am sure you know very well what you are doing (I am doing the same thing also).

    But Troy has not given more details for his project.

    Ioannis

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