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  1. lespaul

    Signal Conditioning Problem

    I forgot about one of the signals. There will be a 700 mV p-p square wave signal that will be riding below vehicle voltage which is about 12-14 V. If I amplify that signal, it will run an amp right to the positive rail and never leave. Thats the reason for the differentiator.
  2. lespaul

    Signal Conditioning Problem

    Max frequenecy is negotiable, but it must be able to do at least 30K. Min frequency is 24 Hz. Max amplitude is 50V and min amplitude is 50 mV. This circuit must also be able to convert square waves with amplitudes .7-1.54 V, 0-4.2V, and 0-12 V. Same frequenecy requirements.
  3. lespaul

    Signal Conditioning Problem

    Skogs, if you are just going to attack me than please do not post anymore in this thread. I've let it go long enough. I don't need your help that bad that I need to take flak from you. Log, The AMP is powered by +/- 15 V. Like I said before I think the problem is with the comparator circuit...
  4. lespaul

    Signal Conditioning Problem

    By decoupling the power supply are you referring to placing a cap between the powers and ground? If thats what you mean, the PCB version of the circuit has those caps.
  5. lespaul

    Signal Conditioning Problem

    The problem is mainly with the passive sensor which produces a sine wave that varies in amplitude as the frequency increases. The active sensors produce square waves that have a steady amplitude as the frequency changes. Those work well for the most part. The comparator should have 30 mV of...
  6. lespaul

    Signal Conditioning Problem

    The circuit that was on the breadboard works in a car, no idea if the pcb version works because I don't have access to a vehicle for testing at this time. I don't see how the connection of the signal source affects anything. In my last post I stated that the signal out of the differentiator is...
  7. lespaul

    Signal Conditioning Problem

    I think the problem is in the back part of the circuit after the differentiator. The signal coming out of the differentiator looks pretty good, but the signal out of the comparator is awful at low frequencies.
  8. lespaul

    Signal Conditioning Problem

    Well, this is eventually going to be used in an automotive DA system. So the signals will be coming from sensors that either have no ground or are referenced to vehicle ground. The DA box will be connected to vehicle ground through the lighter plug.
  9. lespaul

    Signal Conditioning Problem

    The instrument amp has a reference pin that is grounded. When you say I should put a cap across the zeners, do you mean in parallel? The requirements for the circuit are that it has to operate at 27 Hz and 100 mV for the low amplitude sine waves. The upper limit is not of concern as 20K or so...
  10. lespaul

    Signal Conditioning Problem

    Here is the schematic.
  11. lespaul

    Signal Conditioning Problem

    With a larger amplitude (about 500 mV or higher) the output signal is a fairly clean square wave from 0-5V no matter that the input signal. But with smaller amplitudes, the output is still from 0-5V but there are noise spikes all over the place. When the amplitude is decreased beyond a certain...
  12. lespaul

    Signal Conditioning Problem

    It's possible the circuit was on the edge of stability. The original circuit I built was placed into a cabinet and left alone. Not a part on the circuit was touched. When I used the circuit a few months later I had problems. Thats what I don't understand. The circuit is comprised of a...
  13. lespaul

    Signal Conditioning Problem

    Thanks for the help guys, appreciate the courtesy.
  14. lespaul

    Signal Conditioning Problem

    I developed a circuit for a module that transforms several types of signals into a digitally compatible signal. I tested this circuit on a breadboard in January and it worked perfectly over the required range of amplitudes and frequencies. I had some PCBs fabricated about a month ago with the...

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