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FDC1004EVM: Issues with Capacitance reading using GUI

Ishan Panchal
Intellectual 640 points
Part Number: FDC1004EVM
Other Parts Discussed in Thread: FDC1004

Hi There,

I am using FDC1004EVM with the GUI to measure the capacitance. Please see attached files for Register and Configuration in GUI. The CIN1 remains around 7pF at the boot-up. When I move finger close to left pad the reading doesn't change but when I touch it then it goes to 12pF. There is no change in CIN4 at all even after touching it. I am expecting that as soon as I start moving finger close to pad the capacitance reading should start to increase, please let me know if this is not the case.

We have an application where we need to measure oil level without contact, so I am trying to understand the basic functionality of FDC1004. 

Attached are the images of EVM connected, I did made sure the 1-to-1 connectivity of pins. Please let me know if I need to configure the EVM under GUI.

Thanks..!!!

  • 0
    TI__Mastermind 40295 points

    Ishan,

    Bringing up one of our EVMs with default GUI settings and without any nearby objects shows CIN1 = 0.58pF and CIN4 = 3.07pF as shown below.
    CIN2 and CIN3 are N/C and should show little or no change if you touch the sensors.

    Laying a stack of papers over the sensors increases CIN1 and CIN4 by by about 0.1pF, which is as expected.

    A large copper plate only 0.5cm from the sensors increases CIN1 to 1.21pF and CIN2 to 4.34pF.

    It sounds like the CIN1 behavior you have observed is consistent with a working EVM.

    For CIN4, take a look at the sensor waveform with a high impedance probe, and it should look something like below,
    where the waveform period should correspond to a 25kHz frequency, and the peak-to-peak voltage is about 2V.
    The signal was sampled with an attenuating hi-impedance probe, so multiply the amplitude by 10x.

     

    For liquid level detection, you will most likely need a different sensor topology.
    For an example, please take a look at `Capacitive-Based Liquid Level Sensing Sensor Reference Design.

    For more info on the FDC1004 - including liquid-level sensing - please take a look at our E2E FDC1004 Frequently Asked Questions page.

    regards,
    John