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Same waveform when change from 1usec to 10ms — Parallax Forums

Same waveform when change from 1usec to 10ms

irvirv Posts: 14
edited 2010-02-28 17:45 in Accessories
When wiewing a 1 megahertz square wave (ch1 looks good) ,(1 usec/div), then change the rate to 10ms/div,,I see almost the same waveform ???....Irv

Comments

  • HannoHanno Posts: 1,130
    edited 2010-02-22 18:53
    Hi Irv,
    If you sample a signal too slowly, you'll get artifacts. There was a good discussion here: http://forums.parallax.com/showthread.php?p=883088
    Hanno

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Co-author of the official Propeller Guide- available at Amazon
    Developer of ViewPort, the premier visual debugger for the Propeller (read the review here, thread here),
    12Blocks, the block-based programming environment (thread here)
    and PropScope, the multi-function USB oscilloscope/function generator/logic analyzer
  • irvirv Posts: 14
    edited 2010-02-22 20:31
    Yes ,,,I understand about the "Alias",,but you will have to post a warning or something on the panel or do something in software or most folks (students) will not understand...Most digital scopes( Tektronix or Hp) that I have worked with do not have problem with this...Irv
  • HannoHanno Posts: 1,130
    edited 2010-02-28 04:31
    Hi Irv,
    Scopes that quickly sample into a big memory buffer can "average" the data to prevent these artifacts. Unfortunately there is no way to do this with the Propeller. This is documented see section 3 of the Getting Started Guide:
    "Tips:
    - Select the right timescale
    Digital oscilloscopes sample the input signal at configurable rates. (The PropScope samples up to 25 Million times/second) Sampling a signal too slowly will yield artifacts- so always look at a new signal with a faster timescale first."
    Hanno

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Co-author of the official Propeller Guide- available at Amazon
    Developer of ViewPort, the premier visual debugger for the Propeller (read the review here, thread here),
    12Blocks, the block-based programming environment (thread here)
    and PropScope, the multi-function USB oscilloscope/function generator/logic analyzer
  • irvirv Posts: 14
    edited 2010-02-28 17:45
    So far the scope has been very good..I can work around the "alias"..good work..Irv
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