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How to detect rain with FDC1004?

shanqing liu
Intellectual 635 points
Other Parts Discussed in Thread: FDC1004

Hi,

   I am reading FDC1004 datasheet . It  mentions that it can be apply to  "Rain/Fog/Ice/Snow Detection".

   My company have an project to detect rain and haven't found solution.

   When I read TI's  sensor product manual ,I found the similar application in FDC1004 datasheet.

   Can you give me some application case?

   I think this kind of capacitive sensing can work must have a conductor medium with earth(e.g. human body).

   If it can detect rain, what is the conductor medium with the earth?

Thank you.

Best regards,

Liu.

  • 0
    TI__Expert 7400 points
    HI

    Yes it is possible to detect rain with the FDC1004 and capacitive sensing. Typical application is for automotive windshields used for automatic windshield wiping controls. A comb structure sensor is often used to maximize sensitivity based on the size of the water droplets. The gap between the finger of the combs and the width of the fingers are system dependent and should be sized accordingly to get the appropriate sensitivity. usually, the sensor is placed on the backside of the windshield so the water droplets will not directly hit the sensor, it will hit the windshield which is on top of the sensor.

    One comb will be CINx and the other comb will be GND. A shield can be placed on the backside of the CINx/GND layer. Please google comb rain sensor and you will see the structure.

    Thanks
    -David Wang
    Capacitive Sensing Applications
  • 0 in reply to David Wang11
    Intellectual 635 points
    Hi David ,
    Thank you .
  • 0 in reply to David Wang11
    Prodigy 10 points
    Dear David,

    I am currently designing a wetness sensor using the same comb structure (CIN1 and GND) that you described above.
    My question regards to the shielding:
    1. Should I make the same comb structure for shielding (SHIELD1 and GND) on the bottom side of the PCB as on the Top side (so SHIELD1 below CIN1 and GND below GND) or a solid SHIELD1 copper pour would be better?
    2. I need two separate sensor areas so for the second one I will connect the signals to the FDC1004 using coax cables. I will definately shield CIN1 with SHIELD1, but should I also shield GND with SHIELD1?
    3. Should I consider using the Out-of-Phase approach (so using SHIELD2 instead of GND)? Is this method works for detecting rain drops? In this case is the comb structure of the shields (SHIELD1 below CIN1 and SHIELD2 below SHIELD2) a must?

    Thank you very much for your help in advance.
    Peter
  • 0 in reply to Peter Nemeth46
    TI__Expert 7400 points

    HI:

    1. You can have a solid SHLD electrode underneath the comb structure on the top layer. Depending if the application is a floating or grounded system, having the SHLD underneath the ground will create direct coupling to the SHLD thus adds capacitive load to the SHLD pin. The SHLD drivers can only handle up to 400pF, after that, it will be ineffective and saturate. With this in mind, you could possibly only SHLD the CIN electrode.
    2. Shielding ground is not necessary unless it's a floating system in which an interference (ie: a human hand) can cause the ground potential reference to shift.
    3. yes you can use the OOP method, the only benefit is that it will help reduce any non-static parasitic capacitance within the system (ie: hand interference).

    Thanks

    -David Wang

    Capacitive Sensing Applications