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Original question:

FDC1004EVM: sensor for water level

FDC1004EVM: sensor for water level

SRIPRIYA A
Prodigy 60 points
Part Number: FDC1004EVM
Other Parts Discussed in Thread: FDC1004


We have a board with I2C interface. we have made a small PCB with FDC1004 on it, taking FDC1004 Evaluation Module as reference (schematics taken from  TI website).
We have programmed the registers as per register settings given in section 3.7 of "EvaluBd FDC 1004 snau165.pdf" . And making calculations as per document eqaution 1 in SNOA958 (How to Calibrate FDC1004 for Liquid Level Sensing Applications ).
please tell -
1. what should be the value of (Hrl) as given in the equation 1 of SNOA958 (How to Calibrate FDC1004 for Liquid Level Sensing Applications ). We have taken a small cup(few centimeters) for the experiment.
2. As we are using PCB with FDC1004 Evaluation Module as reference, LEVEL sensor & REFERENCE sensor is connected to which of the Cin inputs? Coz i perceive that only 2 sensors have been used as the said documents.



  • 0
    TI__Mastermind 23810 points
    1. Hrl simply adds units to the calculation, so in your example, Hrl could be 1cm. During the next step of the calibration procedure, you will perform the gain and offset correction.

    2. It doesn't matter which inputs you connect to. For instance, if you are only using two single-ended channels, then you could use CIN1 and CIN2.

    I recommend also reading the FDC1004 level sensing TI design:
    www.ti.com/.../TIDA-00317
  • 0 in reply to Clancy Soehren
    Prodigy 60 points

    Used the following formula as per the document,

    Capacitance (pf) = ((Two's Complement (measurement [23:0])) / 2^19 ) + Coffset  (Coffset considering as 0)

     For our measurements, MEAS1_MSB [15:12] always shows to be "0000", making its 2's complement as 0xF. Do we need to take the 2's complement of the nibble even if it shows "0000"?

    And i am getting following values (as i have taken the 2's complement of complete "measurement [23:0] ", its MSB nibble being "0000":

    30.79466

    30.40891
    30.82048
    30.43596
    30.81271
    30.42488
    30.82192
    30.39911
    30.174
    26.17909
    21.85927
    23.19591
    19.86252
    20.8754
    17.9673
    18.34058
    16.66826
    16.72945
    23.87392
    29.08479
    30.54924
    30.2471
    30.69105
    30.25835
    30.70168
    30.27787
    30.72763
    30.30702
    30.73638
    30.31944

    When bringing palm closer to the sensor, the capacitance is decreasing and increasing when palm driven away from the sensor. But the increment is 

    not consistent,It is fluctuating. What could be the reason. Why i am not seeing consistent increment/decrement?