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FDC2214: ground isolation for FDC module

Hendrik Steenland
Prodigy 80 points
Part Number: FDC2214


Hi there, I have been working with the FDC2214 and developed a pretty nice arduino connection to the chip and send the data via serial to a computer to be displayed in VC#

I have noticed that when i touch the mouse of the computer that the sensors are activated even when i am not touching them. I have found the TI application note on this (http://www.ti.com/lit/an/snoa952/snoa952.pdf,and how isolated earth and a ground plane can improve things, and i have observed this myself as well. 

1) I decided that i would try to implement a DCDC isolator (for power ground isolation) and a I2c isolator (for signal isolation,www.ti.com/.../iso1541.pdf). Rather surprisingly i still see that moving the computer mouse is impacting the sensor. 

2) I then tried complete galvanic isolation with a 9V battery and blue tooth and this solution produced perfect isolation from moving the computer mouse. However the batter supply doesn't last longer than 3 hours so its back to the serial cable solution(1) for now.

So is solution 1 wrong? is there any way to use isolator modules to separate the parasitic capacitance of the serial port USB connection from the sensor itself , am i conceptually missing something?

H

  • 0
    TI__Mastermind 23810 points
    Hendrik,

    I'm glad that you were able to find that app note and that you've proven that you can solve the problem with galvanic isolation. Have you tried the "Earth Ground Referenced" solution referenced in the app note? I'm not sure why your solution 1 is not working correctly; we have not tried that ourselves, so I cannot comment about potential pitfalls. Is it possible that there is still capacitve coupling despite the isolator?
  • 0 in reply to Clancy Soehren
    Prodigy 80 points

    Thank you for your reply Clancy

    now that you mention it, i think that isolator for the I2C is a cap based isolator (originally i was looking for opto, but haven't seen anyone make these).

    Perhaps i can get a better effect with a magnetic field based I2C isolator. Ill give it a try, meter around a bit and let you know what i find.

    Any idea as to whether a Faraday mesh might have a protective effect against coupling?

    Cheers

    Hendrik

  • 0 in reply to Hendrik Steenland
    TI__Mastermind 23810 points
    Hendrik,

    That might help. Normally we look at physical shielding to protect from outside influences. It is also important that the shielding be grounded.