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How do you capture this long waveform?

  1. Jan 20, 2009 #1
    I have a 1sec serial data stream and my cheap PC based oscilloscope cannot capture it with good enough resolution where I can read the data.

    What can I do to capture this serial data stream with good resolution? My scope has only edge trigger function.

    I'm thinking of building a circuit that will output a delayed trigger pulse. I hope that this will allow me to capture the stream part by part. Is this a good idea or is there a better way?
  2. jcsd
  3. Jan 20, 2009 #2


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    Science Advisor

    Can you decrease your sampling rate? Alternately, if it's serial data, why not just capture it using a terminal program (for instance, TeraTerm if you're using Windows)
  4. Jan 20, 2009 #3
    when you say decrease sampling rate, you mean increase the time/div? I can capture the whole serial stream but then I can't zoom in enough to read the serial data.

    I can't use a terminal program because it is not your typical rs232 serial data. It's some weird format that I haven't figured out yet. It's about 30-40 bit long per frame.
  5. Jan 20, 2009 #4


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    Staff: Mentor

    Sounds like you're trying to reverse-engineer something, without much equipment... :devil:

    Your idea of multiple delay-triggers sounds like the best alternative. You may have to do some hand-alignment of the boundaries, depending on what the data looks like, and how accurate your delayed triggers are.
  6. Jan 20, 2009 #5
    yeah, you might want to add a delay timer, then play around with resolution until you see something significant. if it's really "weird", then it may be some kind of manchester encoding where you've got a sync bit at the beginning of a transfer. and this is confusing at first because, iirc, the sync looks like two bits but is over a three bit time period. once you figure out the encoding, you might want to look into buying a special purpose bus analyzer, which probably won't be cheap.
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