Need Help With Circuit Explanation

Discussion in 'General Electronics Chat' started by sonic007, Mar 28, 2012.

  1. sonic007

    Thread Starter New Member

    Feb 26, 2012
    I am a beginner Electronics enthusiastic and I am trying to build a circuit and I kind of know how to go about assembling the circuit but I do not understand purpose of some of components in the circuit. I have attached an image of the circuit for your reference.

    - The Purpose of the 6.8k, 100 nF and 680k ?
    - The Purpose of the combination of 100 nF and 680k in the first op-amp and 2nd op-amp ?

    -The Purpose of the combination of 1uF and 68k ?

    Also note shown on this circuit what will be the Purpose of a Comparator and how does it generate square pulse if attached to the two stage op-amp at the IC2 pin 7 ?

    Thank you So much.
  2. SlowCoder

    New Member

    Mar 25, 2012
    * watches with interest ... *
  3. SgtWookie


    Jul 17, 2007
    The opamps are configured as noninverting amplifiers. The 6.8k resistor is R1, the 680k is R2. The formula for the gain of a noninverting opamp with divided feedback is:
    Av = (R2/R1)+1
    This means that each stage has a gain of 101. Since you have two stages in series, and the gain of one stage is multiplied by the other, you will have a net gain of 101*101=10,201.
    Read up here:

    This will tend to decrease the response (lower gain) with rapidly changing (higher freqency) signals.
    Capacitors block DC, and pass the effects of AC. (That's a very important concept; write it down and remember it.) So, the voltage on one side of a capacitor can be quite different than the other side, yet if the signal changes value on one plate of a capacitor, that change can be seen on the other plate.

    The 68k resistor keeps the noninverting (+) input of the opamp's input potential average at ground.

    Opamps are really made for analog applications; where the input and output is a continuously variable signal. Comparators are best used where you want the output to be a "yes" or a "no". Very generally, comparators are much faster to respond to changes in the input signal, as they are not internally compensated as opamps are.

    Sometimes, you can adequately use an opamp as a comparator. However, it's rather like using a hammer to install screws; while it might work, the results would be so much better had you used a drill and a screwdriver.

    If your only tool is a hammer, everything starts to look more or less like a nail. Try to select the most appropriate tool for the job.
    absf and sonic007 like this.