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Thread: DIY O-Scope for tuning OpAmp..

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    Default DIY O-Scope for tuning OpAmp..

    Quis custodiet ipsos custodies?
    Solid State Builders Group

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    Quote Originally Posted by keeperx View Post
    You already have the Oscope, and its laser based.

    there is a bit more to it then this, quite a bit that you would have to do before the ramp, but we used to do this for accelerator 124s and g120s with tropel amps.. Usually we'd start with a 30 hz, four point square.

    To rough tune a Y galvo, input a ramp to the x galvo, in the middle of the ramp, send a long square wave pulse 1/4 the length of the ramp and centered on the ramp to the Y axis. pulse Amplitude is about 5 degrees, and the pulse is just upwards off the zero line and back down. This really just does the damping. It doesnt let you match scanner velocities.

    Sadly the AT Mega based scope doesn't sample fast enough to tune a modern scanner, 12K yes, maybe. 30K, no....

    Sorry, find a faster DSO.

    like this one:

    http://www.fpga4fun.com/Hands-on_Flashy.html

    cheaper to make, too, as the boards are done.

    then read scope tuning method here:
    A good person hosts this for me, it would be appreciated if someone would copy it and host it elsewhere as well:

    http://www.skywise711.com/lasers/scanner/scanner.html

    disclaimer:
    note, I cannot be held responsible if you don't know what your doing when tuning your galvos.

    Before the Benner Unit chimes in, these days you can get a signal source that actually dumps a ilda pattern cheap.
    Even just a laser media pattern off a sound card dac may be preferable for beginners to a scope and square wave method. The reason I'm saying this is I havent tuned a Chinese amp from up from zero, and have no idea when they will oscillate.

    Ideally you use the scope tuning with a 30 hz square wave, a good ilda test pattern, and the other patterns such as laser media and grid.

    However for those times you just cant get a poor grade amp to load up, the scope rules. Provided you dont set the amp into oscillation. You really do want a real time scope for this.

    one more thing, it is best if you have internal or external triggering on the scope, a sound card scope that "free runs" without triggered sync would actually set you back on the tuning.

    Steve
    Last edited by mixedgas; 12-01-2008 at 07:35.

  3. #3
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    Smile More Scopes for your pc

    Hi both,

    Here are some more (free) examples of making a scope:
    (OK, not quite fast but if will give some pictures)

    http://www.circuitsonline.net/download/download/135
    or
    http://www.relisoft.com/freeware/freq.html
    or
    http://www.zelscope.com/
    or
    http://www.circuitsonline.net/download/download/155



    Grz,
    Vince

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    At a time I used a Pangolin's LSD built-in abstract generator to simulate o-scope display for scanners tuning verification. All I did was using a sawtooth at ca.10Hz to one output and a square waveform at double to freq. at the other.
    It nicely shown the over and undershoot in an oscilloscope style view.
    Piotr.K

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    mixedgas's Avatar
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    as long as the sample rate at a minimum is at least 2.1 x times the point rate, ie for 30K galvos, you'd need a 60.2 Khz sample rate, you can get started with scope tuning

    Additionally, some DSOs have roll mode for recuring waveforms, , aka equvalent time sampling, where they build a picture up over a long period of time using a lower sample rate, at the cost of you tearing your hair out waiting for the view to update.

    really if I'm tuning at 30K, I'd want a 90K sample per second, 32,000 sample depth machine.
    60K and 2K sample depth dont cut it, its like looking at the scope through a 320x480 screen.

    This makes a older sound card at 44k Sample per second, suspect when you use it as a scope.
    Aliasing and Nyquist show up just as much in digitizing scopes as they do in audio.

    Or just buy a used 100Khz response old analog scope on the bay for 40$ and not have to worry about anything but shipping and the crt breaking.

    Steve
    Last edited by mixedgas; 12-01-2008 at 15:06.

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    mixedgas's Avatar
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    Last edited by mixedgas; 12-01-2008 at 15:10.

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