sound car scope output

Discussion in 'General Electronics Chat' started by jut, Jun 8, 2009.

  1. jut

    Thread Starter Senior Member

    Aug 25, 2007
    224
    2
    Hello,

    I'm using a dsPIC from Microchip for the first time, and just for fun, I've got an old quartz crystal with two electrodes and a glass enclosure. I'm not sure if the nominal freq. printed on the side (4.8 MHz) of it is accurate/correct. I've configured the PIC to give me a working freq. of 10 MHz. To test this, I'm toggling a digital output whose period is 60 ms.

    I don't have a real scope, so I've been experimenting with sound card pc oscilloscopes. Of the many out there, I've found Zelescope to be the best (not free, $10).

    Anyways, here is a screen capture. The square wave starts to decay to zero after it switches levels. So there is a high pass filter inside the sound card blocking DC? Can someone offer more insight here?

    [​IMG]
     
    Last edited: Jun 8, 2009
  2. S_lannan

    Active Member

    Jun 20, 2007
    247
    2
    looks like it. Try it at 500hz and 1Khz. see what happens
     
  3. jut

    Thread Starter Senior Member

    Aug 25, 2007
    224
    2
    Looks like it can resolve a 10 kHz, barely. I'm sampling at 96 kHz.

    [​IMG]


    Not to shabby :D
     
    Last edited: Jun 8, 2009
  4. S_lannan

    Active Member

    Jun 20, 2007
    247
    2
    yeah not too surprised. I've never really been a fan of PC soundcard scopes, but I'm sure there are plenty of things you can use them for even with the extremely limited bandwidth.
     
  5. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,535
    And there are lots of free packages out there. The USB versions are better, but they have problems too.

    Keep your eyes out for a deal. You never know, I sure didn't expect to find mine for $10, but they were in quantity, so I made sure I had enough for my friends too. (working $10, dead $5). The scope is pretty low value, but it has HP stamped on the front, so where it does work it's OK.
     
  6. jut

    Thread Starter Senior Member

    Aug 25, 2007
    224
    2
    Bill, where did you get it? Ebay? What's the mfg/model? I'm curious b/c I'd be interested a cheap scope, but something better than the sound card.

    thanks.
     
  7. jut

    Thread Starter Senior Member

    Aug 25, 2007
    224
    2
    Turns out this sound card scope is slightly useful. Here is a shot of the SPI bus from the PIC18f2520 to a serial EEPROM (25AA1024).

    [​IMG]

    I should mention the PIC is running at Fosc = 125kHz and the SPI Clock is Fosc/64 = 1950 Hz.
     
  8. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,535
    Hams are a great source, I went to a HAMfest (amature radio). I got mine from what used to be a regular HAM flea market. eBay is also a good resource.
     
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