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A lump in cord design...

Discussion in 'Electronic Design' started by Howhurley, Sep 22, 2007.

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  1. Howhurley

    Howhurley Guest

    I've got a situation I hope one of you wonderful circuit designers can
    help me with. In a three wire (+24VDC, DC GND, and a 12-24 signal
    from a PLC, perhaps 100 ms in length) I need to come up with a
    monostable ramp signal from 0 to 10 volts, no more than 10-15 mA,
    approximately 1 sec in duration, adjustable in slope.(gain)

    Three thoughts I had were:

    1. A simple RC circuit, (non-linear, I know, but buffered with a
    cheap op-amp front and back to even things out)

    2. A 555 timer/oscillator to charge a cap until it hit a certain
    point on an op-amp comparator which discharged the cap...the voltage
    level would then be tracked by a unity gain follower and actually be
    my output.

    3. A simple 8 bit d-a, charged by a oscillator circuit,

    4. Of course, a simple rabbit or pic microcontroller...but that's for
    the future.

    Any ideas? I'm a sales guy that sells industrial stuff, and some of
    the things I sell are ideas on how to do things. I quoted a job,
    assuming that this type of thing was available, and, well, you know
    about assuming things.

  2. Joel Kolstad

    Joel Kolstad Guest

    I'd use an op-amp as in integrator (like your RC idea, but you'll get a linear
    output) and then either build the monostable "part" out of discrete
    transistors or use some 555-like device if you can get one for 24V. I'm
    trying to avoid your needing a voltage regulator here, although if your 24V
    isn't that well-regulated, it'd affect the ramp rate... which could actually
    be good or bad, depending on whether you want the adjustment to be in
    volts/second or percent of full voltage output/second.

    The Art of Electronics has all you need to know about building op-amp
    integrators if you don't already have a reference.

  3. Fred Bloggs

    Fred Bloggs Guest

    Well you need to tell us the relationship between the "12-24 signal"
    from the PLC and the slope/duration of the ramp output, dontcha think?
    And what does "lump in chord" have to do with anything? We can't read
    your mind.
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