Auto adjusting op amp circuit

Discussion in 'The Projects Forum' started by 7Arrows, Feb 14, 2010.

  1. 7Arrows

    Thread Starter New Member

    Feb 14, 2010
    11
    0
    Hello to every one
    Can anyone help me with this circuit? What I need is to null an op amp with a sample and hold circuit. The circuit will be running at 1KHZ it needs to sample at the first part of the cycle and null the op amp for environmental conditions then hold through the rest of the cycle when the op amp receives its main signal. This is for the final receive stage of a pulse Induction metal detector. Will this circuit work or am I going down the wrong road.
    7Arrows
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Without doing a detailed analysis, it looks to me that the zeroing signal is attenuated by ~1/100 by the R23/R3 voltage divider. I don't think that is what you intended.
     
  3. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    My first impression of the circuit is that IC7.4 is a transmission gate that is used to reset the integrator formed out of U8A. You take the control line of U7.4 active and the integrator capacitor is discharged to prep the integrator for the next cycle.

    Can you supply us with more details of what you are trying to accomplish?

    hgmjr
     
  4. 7Arrows

    Thread Starter New Member

    Feb 14, 2010
    11
    0
    IC7.4 is a Bilateral Switch that closes at the start of the cycle to samples IC8.A to charge a sample and hold circuit C20 and IC8.B that is needed to null IC8.A then IC7.4 opens. The rest of the cycle is used to process a signal from the search coil. In a normal circuit IC8.A would be set with a potentiometer on the control panel. The problem with adjusting IC8.A manually is that ground conditions can change quite fast there for needing frequent adjustments. I’m trying design the circuit to automatically adjust IC8.A.
    Thank you for the help.
    7Arrows
     
    Last edited: Feb 15, 2010
  5. 7Arrows

    Thread Starter New Member

    Feb 14, 2010
    11
    0
    This is the original circuit I trying to modify. I want to replace VR4 with some kind of circuit that will do the same as VR4 during part of the cycle then hold through the rest of the cycle.
    7Arrows
     
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