Comments needed for a USB oscilloscope project

Discussion in 'The Projects Forum' started by cyberfish, Jun 5, 2010.

  1. cyberfish

    Thread Starter New Member

    Jun 3, 2010
    10
    0
    I just finished the schematics for my project - a 100Msps, ~50MHz USB Oscilloscope based on a FPGA.

    http://cyberfish.wecheer.com/blog/?p=441

    Comments much appreciated! I'm sure there are oversights everywhere :p.

    Many thanks
     
  2. Acce

    New Member

    Mar 4, 2010
    4
    0
    Hey man, it looks great just looking at the specs! I'm afraid I'm not someone who is able to do much checking on it though, for now.

    As for software side, I have a suggestion:
    Do (or get someone else to) use already existing code; I'm talking about xoscope (based on GTK+ 2.0) or Osqoop (based on qt4). Another option could be adding device to Comedi -library. For example, xoscope already supports comedi (atleast I got that impression).

    I'm interesting in building my own PC oscilloscope too, but I think for now I'm going to try and do something simpler than your cool device is.
    I'm not that much of a coder myself yet, but I could maybe help with something and I'm sure someone active with the projects I mentioned would be interested in your hardware.
     
  3. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    Hey, that looks cool. What is the cost of the parts? I am starting to think about building this :)
     
  4. windoze killa

    AAC Fanatic!

    Feb 23, 2006
    605
    24
    Well done.

    Just remember to follow all the rules for making the PCB. If yo are working at frequencies up to 50Mhz then you will need to apply a bit of impedance matching to some of the track. I assume if you have gotten this far you have already thought of all those things.
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,119
    3,043
    If simple means low frequency (ie. audio), then you can just use your computer's mic or line in port and some of the great oscilloscope software out there. I've recently done this with great success, for a project where I only needed frequencies from almost DC up to ~10K.

    The only problems I've run into are noise and ground loops, and the OP should learn about this plague on all oscilloscopes. Noise is easy to get rid of using shielded cables, but ground loops are forever. Basically, the 'scope and the device under test need to be grounded to each other, but this is a problem if their power supplies are not completely isolated from each other. Current can flow from one ground to the other.

    In practice this means being extremely careful to protect your inputs from unexpected currents caused by the ground loop. Don't even think about using AC mains as a handy source of a sine wave! If your power supplies are isolated, eg. device under test is battery powered, no worries.
     
  6. Acce

    New Member

    Mar 4, 2010
    4
    0
    @Wayneh:
    Yeah, I have been reading a lot about them, and it could serve well at first, but I was thinking about later making one using schematics from DPScope, only changing the microcontroller from PIC to MSP430 or AVR.
    (sorry this is kind of offtopic)
     
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