trying to help a developer (Ben Levitt) to track down a bug on my UavDevBoard system, it was hard to explain by email the strange behavior.

After he suggested me to try with a sound card oscilloscope, I decided to try something I was planning from sometime now : a soundcard oscilloscope.

I build a voltage divider to scale down PWM voltage (3.3V) to about 0.7V, which is more suitable for a PC audio input.

I crimped a couple of cables with servo connectors on one side and a stereo mini jack, from a boken headphone on the other side.

The interface is double channel capable, but some PC (like my laptop) only has mono input.

On the picture above you can see a double channel PWM signal from two different UavDevBoard outputs.


As soundcard oscilloscope I use Zelscope, which is ridiculously cheap, and Visual Analyser, which is free instead.


Here you can find a little tutorial, with schematics and pictures, I did about all that.


Best regards,



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  • Hi Riccardo,


    Both links work perfect now. So perhaps it was me who did something wrong.

    I never knew it is this simple, i will test it right away!



  • wow ! great software, its working well....and good tool at ur desktop itself.
  • Hamish,

    if you read carefully instructions on the link you provided, under hardware, you can see that they say :
    1) transmitters are usually overload protected by a fuse
    2) sound cards are usually protected for overvoltage
    3) they recommend a 1/10 resistors ratio, which steps the voltage down to 0.3V.
    They are really more conserative than me :)
    Up to everyone how to risk their equipments ...

    Best regards,

  • I've been using smartpropoplus http://www.smartpropoplus.com/dnn/ for a while to fly sims using my Tx

    It takes a PPM soundcard input and decodes everything and sends it to a virtual joystick, and comes with a couple of PPM analyses utils


    I crudely tap the Tx ppm straight into the line-in and it works, and my soundcard hasn't been fried yet despite frequent use.

  • Hi Bill,

    thank you very much !
    Considering only the free software, this costed me the couple of servo connectors, say few cents.
    It was nice to see how fast Ben was able to catch the bug after he received those files.
    ... and I learned something new again.

    Best regards,

  • Roel,

    thank you :)

    About the tutorial that's very strange, because I set it public on the web. I checked it again to be sure. I checked the link in the post also and all is working for me. Please let me now if you still have problems.
    The full link is this :

    Best regards,

  • T3

    Hi Ric,

    That is super. It is going to be a big help to the community.

    Sometimes when I am trying to help someone, I wish they had a scope to look at the waveforms, but the "real ones" are rather expensive. With your approach, you can get basic scope functionality without spending a lot of money.

    Thank you.

    Best regards,


  • Great work! I always wanted to make one of those.

    I'd like to know a bit more on the subject so i tried to open the tutorial, but it says it is unable to retrieve the document, probably because you didn't set the permissions right.

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