Two capacitive input for AD7747

I need two capacitive input for my application in using AD7747 for grounded sensing. The AD7747 only has one input and I wander if I can use the AD7746 instead. However, I'm unable to shield my setup well enough for floating sensing using AD7746 which makes it unsuitable for my application.

Is there a way I can use the AD7746 for grounded sensing perhaps by connecting the excitation pins to the input pins?

Or is there another device used for grounded sensor (similar to the AD7747) that has two capacitive input?

Thanks for your support!

  • 0
    •  Analog Employees 
    on Sep 8, 2014 7:25 PM

    Hello Idowu,

    The AD7746 cannot be used for single electrode sensing; shorting the Excitation pins to the CIN pins will saturate the readings of the sensor.

    The AD7747 is the only single ended device in this family, but you could look at the CapTouch family: AD7143, AD7148, AD7147/A, AD7142.

    Regards,

    Sean

  • Thanks for your quick response!

    My application is for liquid level sensing in a small container therefore AD774x seem to be most suitable. In that case, is there a way to shield my capacitor - that varies based on liquid level (for liquid level sensing) from capacitive touch? I have tried to insulate and cover the two plates with a grounded metallic shield, however, I still get substantial interferences due to touch or motion using AD7746. On the other hand, it works for the grounded version using AD7747.

    Is there a better way to shield the plates or sensor from artefacts due to touch or motion?

    What is the advantage of using a floating setup/sensor (AD7746) over a grounded sensor (AD7747) for liquid level detection?

    Thanks again for your help; best!

  • 0
    •  Analog Employees 
    on Sep 9, 2014 1:46 PM

    Hello Idowu,

    The grounded metallic shield is the recommended method. The CDC is sensitive to "all" capacitance changes, so the "art" is restricting the changes to only the ones that you are interested in.

    The grounded sensor tends to have more sensitivity for a given sensor area than the floating sensor.

    Regards,

    Sean

  • Are there any references on board designs for interfacing arduino and AD7142?  How did you interface the AD774x to your microcontroller? Please let me know. Thanks.