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  1. #1
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    ultrasonic op amp

    Hi! I desperately need help concerning the circuits I've attached below. Basically, it is an ultrasonic receiver circuit, with two ultrasonic receivers connected. The first circuit shown is just for one ultrasonic receiver.



    The op-amp labelled A is used to amplify the signal while the second op-amp labelled B acts as a comparator. It's a simple concept but for some reason, the circuit does not work. I've tried to test op-amp A by itself and have disconnected all connections to op-amp B. However, the output from opamp A is not amplified at all. So far, I've been using a signal generator to supply a 40kHz signal in place of my ultrasonic receiver. There is definitely nothing wrong with my circuit connections or the breadboard as I've reconnected everything, had a lecturer check the connections and changed breadboard several times already.

    I've tested three different types of op-amps, including OPA2340 (as suggested in the circuit), LM833N and UA741 and none of them work. I've even bought new op-amps but I still don't get an amplified signal. What I do get is either the exact same waveform, or a waveform with smaller amplitude. Also, whether or not there are signal inputs in place of the ultrasonic receivers, the DC output of Op-amp A is the same as the voltage supplied at Vcc for the opamp chip.

    This is the full circuit:



    Theoretically, the circuit is sound (to me at least). Is there something opamps require that I'm not aware of? I would be grateful for any suggestions or help at this point as I've been troubleshooting this circuit for two weeks. Also, if instead, any of you have a suggestion of replacement components or circuits that works the same way, I would also be grateful to have them!

    Please help! I need a solution ASAP!

    Thank you!

    •   Alt30th June 2005, 13:15

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  2. #2
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    ultrasonic receiver circuits

    Configuration of components around opamp A indicates inverting amplifier and the inputs labels show that you connected input (+) to where input (-) should be connected and opposite way around.
    Swap the inputs and you should be OK..
    Regards,
    IanP



    •   Alt30th June 2005, 13:37

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  3. #3
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    ultrasonic opamp

    Unfortunately, I have tried switching the connections to the input pins but it doesn't work either. I forgot to mention that. Could there be any other possible mistakes with the circuitry?



    •   Alt30th June 2005, 16:04

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  4. #4
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    ultrasonic opamp

    Clearly the inputs of opamp A are swapped. I understand you have corrected that.
    Other than that, there is no reason why the circuit would not work.

    Check the connections and part values carefully.
    Check the voltage at pin 3 of opamp A (after you swap the pins). It should be about 5V. If not, one of the resistors R11, R12, R14 is bad, is the wrong value or the connections are bad.
    Check the DC voltage of opamp A. It should be about 2.5V. If it isn't, check the resistor R15 and the connections. (Also, make sure C11 is not shorted).

    Apply the signal and measure the output of opamp A. It should be 75 times the input signal. If not, check the values of R14, R15, C11. Check C11 is not open.

    Good luck!



  5. #5
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    Re: ultrasonic opamp

    any help regarding usin tl072 instead of 2340

    ---------- Post added at 17:55 ---------- Previous post was at 17:54 ----------

    any help regarding usin tl072 instead of 2340



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