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FDC2214EVM: Connection for Custom designed sensor with FDC2214EVM

Shantanu Pal
Prodigy 110 points
Part Number: FDC2214EVM
Other Parts Discussed in Thread: FDC2214

Hi,

I am using a custom-designed PCB as a sensor along with the FDC2214EVM. The sensor I am using having one circle at the center and two concentric rings with bigger diameters. Here, I am using the circle at the center and the outermost ring as two plates of a capacitor. According to the datasheet of FDC2214 to measure an unknown capacitance, one terminal of the capacitor has to be connected to one of the channels of the evaluation board and the other terminal of the capacitor has to be connected to the ground. Hence, at present I am connecting the circle at the center of the PCB to CH0 and the outermost ring to the ground point on the EVM pcb.I have shown the connection in the attached figure. The logic I am trying to implement is that as the sensor PCB moves across a surface with considerable change in material permittivity, it will show a change in capacitance at the output. Kindly let me know whether the type of connection is used  to implement my idea is correct or not.If this is not the right approach, please suggest me the correct configuration.KindlyFDC2214_Connection.pdf see the attached figure for further clarification.

with warm regards,

Shantanu

  • 0
    TI__Expert 8050 points
    Hi Shantanu,

    Instead of using ground, you can connect the outer ring to the other input of CH0, i.e. connecting the two electrodes to IN0A and IN0B.

    What is the purpose of the middle ring in your current setup?

    Alternatively, you can try connecting the inner circle and outer ring to one input, and connecting the middle ring to the other input.

    Regards,
    Yibo
  • 0 in reply to Yibo Yu
    Prodigy 110 points
    Hi Yibo,
    Thank you so much for your reply and useful suggestions. I have a small doubt here, initially I have connected the inner circle of the sensor to IN0A and the outer ring of the sensor to ground just to emulate an variable unknown capacitor one plate of which is connected to the ground and the other plate is connected to Cap Sensor 0 (as mentioned in the circuit given in the datasheet). Now if I connect the inner circle of the pcb to IN0A and the outer ring of the pcb to IN0B, I believe it will act as a variable unknown capacitor which is connected in parallel with the Cap Sensor 0 (but not connected to ground). Can you please comment on any specific advantage in using the configuration that you have proposed compared to the last one? I will be really interested to know about it more.

    To answer your question: here I have tried to develop concentric coplanar capacitive sensor using circular and ring structures. To implement this basically the inner circle and one concentric ring outside the circle is enough. But, I have used another ring in the middle to exercise some additional control over the generated field profile, which I am planning to use at later stages of the experiment.

    Also "connecting the inner circle and outer ring to one input, and connecting the middle ring to the other input" - is one configuration among various permutation and combination of the circle and two rings that I am planning to use for my experiments to find out which configuration works best for me. Your suggestion have made me more optimistic in this regard.

    Eagerly looking forward for your further comments on my questions.

    with warm regards,
    Shantanu
  • 0 in reply to Shantanu Pal
    TI__Expert 8050 points
    Hi Shantanu,

    The two inputs are driven by half sine waves. When IN0A is active, IN0B is grounded, and vice versa. If you connect one of the inputs to GND, then during half of the cycle both inputs are effectively grounded. In general, you can get a greater frequency shift by measuring the capacitance between IN0A and IN0B.

    Regards,
    Yibo
  • 0 in reply to Yibo Yu
    Prodigy 110 points
    Dear Yibo,
    Thank you so much for your time and valuable response.

    with warm regards,
    Shantanu