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Designing a circuit to sample magneto ignition signal.

Discussion in 'General Electronics Discussion' started by dandy1, Jan 27, 2020.

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  1. dandy1

    dandy1

    3
    0
    Jan 26, 2020
    I want to capture the signal from a magneto ignition to interpret the rpm of a small engine.

    with reference to this thread: https://www.electronicspoint.com/forums/threads/magneto-kill-terminal.288631/ these are the types of ignitions which are common on small engines.

    and this output:
    (courtesy of Debe)
    [​IMG]
    this is not my output but illustration for what I am looking to achieve.


    I am trying out this circuit:

    Ign1.GIF

    which works with some conditioning in software but there is a lot of noise encountered on the signal line which is totally erratic.

    Its a bit hit and miss because the software is implemented to ignore pulses shorter than
    X and longer than Y to avoid the erroneous readings which really limits the bandwidth at which i want to sample: 600-6000 RPM or 10-100 Hz.

    On the other hand sometimes the circuit completely misses a pulse so at 3000 RPM i will get a reading of 1500,

    I use this circuit because it is really simple and I want it to be compact. But I am willing to bet there is better way to do do it, maybe with better spec'd components or a different circuit altogether?

    ideally i would also like to implement some filtering too, I've tried out some caps before and on the signal line but really that is a step beyond what i understand about electronics.

    Any advice much appreciated

    A
     
  2. debe

    debe

    276
    72
    Oct 15, 2011
  3. dandy1

    dandy1

    3
    0
    Jan 26, 2020
  4. debe

    debe

    276
    72
    Oct 15, 2011
    They are $13 Australian & they are all you need if you want engine RPM & hours run.
     
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