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Simple triggered sweep.

Discussion in 'Electronic Basics' started by Steven Swift, Nov 22, 2005.

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  1. Steven Swift

    Steven Swift Guest

    Greetings.

    A short while ago, I posted a request for links to simple triggered
    sweeps for older recurrent timebase oscilloscopes. I spent a fair
    amount of time looking in old magazines and circuit handbooks, but
    didn't find what I thought I was looking for.

    So I decided to cobble-up a homebrew of my own. This circuit probably
    has been done before, but it met my criterion of being really simple.
    I used already on-hand parts, so the design is far from optimum. It
    works fine on an Eico 460 up to about 1MHz. No attempt was made to make
    a calibrated sweep. You could use a 5v rail and an HC4538 to make a
    nice high speed triggered sweep.

    Have a look at:

    http://novatech-instr.com/Fun/trig.pdf

    Thank you to all of you who sent me emails and posted comments on these
    boards.

    Steve.
    Seattle,WA.
     
  2. I think you could use an LM361 comparator in place of the front opamp.
    It produces high going and low going digital outputs that you can
    enable separately, so you can choose whether you want to sync on
    positive going or negative going edges, without changing the switching
    threshold.

    It will also clock the flip flop a lot faster than an opamp will.

    http://www.national.com/ds.cgi/LM/LM161.pdf
     
  3. Steven Swift

    Steven Swift Guest

    Yup, good call! I actually have a 361 based circuit I built a long time
    ago. It works to about 50MHz. It is overkill for this purpose, but
    would be the right choice, along with an HC4538, if someone wanted to
    modify this and go to higher frequencies. You actually have to move
    some pins around on the 4538 to make it non-retriggerable.

    On the 361 board, I use long-tailed pair miller integrators to get near
    perfect sweeps. But that was a complete homebrew scope I designed in 1978
    or so.

    Thanks.

    Steve
     
  4. Yukio YANO

    Yukio YANO Guest

    It would seem to me relatively easy to replace the horizontal sweep
    oscillator with a 555 chip ! and trigger it with a sample of the
    vertical Amp. signal !

    Yukio YANO
     
  5. And as I pointed out in the previous thread, that wave thirty years
    ago of adding triggered sweep to older scopes did all use 555s for
    the ramp generator.

    I cleared off the scanner, and
    http://www.cam.org/~blackm00/ramp.jpg
    is the scan out of Howard Berlin's "The 555 Timer Applications Sourcebook
    with Experiments" from 1976. The actual circuit was originally in Electronics
    magazine for October 11, 1973, which I likely do have (at least
    the part with the circuit) somewhere but can't be bothered looking.

    And as I said, this basic circuit did seem to be the basis of
    all those "add triggered sweep to your oscilliscope" articles
    from thirty years ago. As I recall, they were all basically like
    this one.

    Michael VE2BVW
     
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