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ramp time to voltage

Discussion in 'Electronic Design' started by [email protected], Apr 28, 2005.

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  1. Guest

    I have a bunch of x y flatbed recorders and I want a simple rising
    volatge to simulate passing time on the x axes. I can work from a
    diagram and know some basics. HP made this in a small package.... HP
    17108A.... anybody have one?
    I can take MV or volts 1-10.
  2. Dan Hollands

    Dan Hollands Guest

    Two approaches of many

    1. Use a binary counter with appropriate weighted summing resistors
    connected to the outputs
    Adjusting the clock rate into the counter determines the rate of rise. The
    number of stages in the counter determines the resolution.

    2 Use a microcontroller with an analog output such as Analog Devices ADUC812


    Dan Hollands
    1120 S Creek Dr
    Webster NY 14580
  3. Dual 12-bit voltage-output DACs. One of the few with such a
    peripheral, but rather slow and power-hungry.

    Best regards,
    Spehro Pefhany
  4. Rock

    Rock Guest

    You could keep it simple by using an LM334 constant current IC (3 pin
    device) by National and discharge it into a capacitor. You can tweak
    the current on the LM334 with a pot, and make a nice linear ramp. This
    is a 3 part solution, not including any power supply.

  5. Add an opamp to make an integrator and you get a buffered output.
  6. Guest

    Thanks everybody, most of you are over my head. I would like at least
    one hour at one shot. I would like a diagram,( I could build heath
    kits) I'm not in the electronics trade.
  7. John  Larkin

    John Larkin Guest

    Most of the flatbeds had high (often infinite) input impedance on the
    low voltage ranges. So a simple resistor-capacitor will make a nice


    *--------100K res------10meg pot----------*--------*---------to recorder+
    | | |
    | | |
    + | + |
    9v battery capacitor switch
    - | - |
    | | |
    | | |
    *-----------------------------------------*--------*--------- recorder -

    The capacitor size depends on how fast you want to sweep and which
    range of the recorder you're on. Try 10 microfarads to start, 1 volt
    range maybe. Stay at 1 volt range or preferably less, otherwise the
    sweep will get nonlinear.

    Open the switch to run the ramp.

    Ignore all the complicated electronics suggestions.

  8. Jim Thompson

    Jim Thompson Guest

    And that guy behind the curtain ;-)

    ...Jim Thompson
  9. For one hour, you'll probably do best with a CMOS 555 feeding a
    74HC4040 feeding a R-2R ladder network. Maybe someone feels like
    drawing it up.

    Best regards,
    Spehro Pefhany
  10. He said "an hour at one shot". 3600 uF cap or giga-ohm resistors?

    I would say attach the minute hand of a clock to a rotary pot; use a
    multi-turn pot for a multi-hour delay.

  11. Joerg

    Joerg Guest

    Hello Dan,
    Or a DAC08, or two of them for more precision. These should be found in
    the bins of any decent lab and would save a lot of resistor matching and

    Regards, Joerg
  12. Joerg

    Joerg Guest

    If you are in a lab look around whether one of the function generators
    allows for really long timing. Sometimes they will indicate in
    "milli-Hertz", sometimes as period times. Only digitally controlled ones
    will be able to do that. That way you may not have to build anything.

    Regards, Joerg
  13. Fred Bloggs

    Fred Bloggs Guest

    Will this be running off the line? Maybe two opamps and an 6-bit counter
    at the core...Do you know enough to build a small DC power supply, or
    any other construction techniques?
  14. John Larkin

    John Larkin Guest

    10,000 uF isn't a huge cap. Or use one of those 0.47F ultracaps.

  15. How fast will that 0.010 F electrolytic self-discharge? The tolerance will
    not be so nice either.

    I see a lot of +80%/-20% with the double-layer capacitors. A mechanical
    clock and a pot would be much more accurate. The error is all due to the
    nonlinearity of the pot, and that doesn't accumulate. Or use a PIC.

  16. Ken Smith

    Ken Smith Guest

    I suspect it would be easier to find a complete DAC than an R-2R ladder,
    but the idea is a very good one.
  17. Guest

    Thanks John, NOW, I understand.
  18. Guest

    The flatbed is line voltage. I can build but not design. Can do vdc.
    Is a discharging cap more linear? I can run my flat bed x axis
    backwards if this helps.
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