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How to set automatically unknow trigger levels?

Discussion in 'Electronic Design' started by [email protected], May 10, 2007.

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  1. Guest

    Does somebody know how can I solve this problem?
    I need to find out electronically the highest and the lowest voltage
    in order to set automatically
    two trigger levels of a unknown signal with range +10 and -10V,

    For instance, once the unknown signal amplitude reaches 8V as the
    maximum value and 2V as the minimum, hence
    I need to set the trigger levels of a comparator for activating other
    devices with relays at the max and min. But the next
    time it will reach 7V and 1V respectively.

    Because the input signal and the trigger thresholds are not constant,
    I do not know how I can solve this in the cheapest way as possible.

    Any advice is appreciated.

  2. What do you mean with "the next time", how much delay between itterations?
    How fast does the signal change?
    It would seem that two DACs controlled by a micro could the set the input
    levels for the comparators depending upon how fast this all has to work.
  3. Why use a mainframe computer when an analog integrator will work?

  4. Sure, and by what signal ist the integrator
    controlled ? Meaning what is the input of
    the integrator ? There might be multiple
    trigger density maxima between the voltage

  5. Mainframe? The OP didn't even describe an algorithm explaining how the
    levels would be chosen, how do you know that an integrator will suffice?
  6. MooseFET

    MooseFET Guest

    Basically what you want looks a little like this:

    IN-------!+\ D1 U2
    ! >----->!----+-----!+\
    ---!-/ ! ! >---+--OUT
    ! C1 === --!-/ !
    ! ! ! !
    ! GND --------+
    ! !

    If the input goes above the output, the output of U1 swings positive
    and charges up C1 to bring it to a matching voltage. When the input
    starts to fall, U1 swings back down, the diode back biases and the
    output remains at the positive value.

    Now all you need is a voltage divider and comparitor to make the
    signal you want.

    This design has some serious problems, however. There is no path for
    C1 to ever discharge. If the frequency is more than a few KHz, U1's
    job is near imposible. D1 has to be a very good diode. U2 has to
    have low bias current but be fast.

    Each of these can be solved in specific cases so if we know more about
    the frequencies etc, we may be able to go further or perhaps just this
    little push start will have you see how to solve it.
  7. D from BC

    D from BC Guest

    Perhaps...check out the min-max detector,
    Patent 4315220
    4 diodes, 1 op amp and a capacitor
    See google patents for sheets.
    D from BC
  8. JeffM

    JeffM Guest

  9. Automatic setting of unknown values is best done in programming using
    random number generator(s) and praying.
    Note: can drive anyone loco, including working hardware.
    BTW this is "design" gathering, try to fit.

    Have fun

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