Measurement conversion

NarrenNarren
in Technical questions
I had an old openQCM unit which broke. Then I built a custom one with a DDS and AD8302. That is running successfully. The only issue is that I get response like an impedance curve. I showed that as the black curve in the attached image. I would like to convert that to a peak (red one in the image) so that I can fit Lorentz function on that. Can someone please explain how to do that. Appreciate your help


Comments

  • raffaele.battagliaraffaele.battaglia
    Hi Narren,
    The reason why we obtain a curve like the red one is due to the use of an additional component: AD8302 (https://www.analog.com/media/en/technical-documentation/data-sheets/ad8302.pdf), using the configuration shown in Fig. 4. Basically, we perform a comparison between the signal output from the DDS (INPB) and the one output from the quartz sensor (INPA). I'm attaching a screenshot of the circuit section to be inserted.
  • raffaele.battagliaraffaele.battaglia
    Sorry, I hadn't noticed that you had already included the AD8302. Did you follow the same circuit that I attached? It could be that the calibration (peak detection) intercepted a secondary peakRetry
  • NarrenNarren
    Hi Raffaele

    I really appreciate your response. Below is a brief image showing AD8302. It is pretty close to what you shared except the capacitor values on the input. I do have buffer/amplifier OpAmps after the DDS and QCM to keep signal stronger.



  • raffaele.battagliaraffaele.battaglia
    You are welcome and thank you too, for your interesting question. I believe that the best way is to share with you the circuit schematic of openQCM Q-1, so you can verify all the differences.
  • NarrenNarren
    Thanks Raffaele. I'll get some inspiration from your schematic. Does this provide the resonance frequency peak by default from the AD8302 or do I need some data processing in the microcontroller or my pythong .
  • raffaele.battagliaraffaele.battaglia
    It is a pleasure. You should elaborate the data via firmware and software. Both are open-source, so, you can analyze them freely: https://openqcm.com/openqcm-q-1-software
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