Capability of EVAL-AD7147

I'm new to analog circuits so forgive me if this is a simple question. I'm interested in using a EVAL-AD7147 to measure some external capacitors. From what I saw in the data sheet the CIN pins have already been linked to the example capacitors on board. Is it possible to connect them to external capacitors?

Thank you for your assistance.

  • 0
    •  Analog Employees 
    on Mar 14, 2014 8:43 PM

    Hi,

    The EVAL-AD7147 does not have a facility to connect an external capacitive sensor without modifying the board. The there is an option to connect the power and I2C lines from the board to an external device, so in this case you could build up a small AD7147 board with your required sensors, and connect through J1 or J2 to the EVAL-AD7147's ADUC841 microprocessor. You will need to set the switch on LK1 to OFF, to disconnect the on board AD7147 from the system.
    When you connect this way, you will be able to carry out your evaluation of the AD7147 on your board using the EVAL-AD7147 board's microprocessor and the supplied evaluation software.

    Can you share what your application is?

    Regards,
    Darragh

  • Thank you for your informative answer.

    I believe the AD7147 I am referring to has a SPI-interface instead of a I2C one (the I2C model is called EVAL-AD7147-1).

    I know that the sensor capacitor would be grounded on one electrode and the other connected to one of the CIN pin of the chip. Is that what J1 or J2 does? How about the shield line?

    My application is an array of capacitors which is formed with liquid metal embedded in polymer film. My goal is to read these noisy capacitors. They have bare wirings coming out of each electrode. Each has a representative capacitance of 1 uF. I am also looking for a way to properly connect them to the PCB.

    Thanks!

  • 0
    •  Analog Employees 
    on Mar 25, 2014 2:53 PM

    J1 or J2 are only for connecting to the communications lines between the AD7147 and the ADUC841. The AD7147 currently does not have a method to interface your sensors to the onboard AD7147. I would recommend that you use an external custom pcb with an AD7147 and your design of sensor, which you can then connect to the EVAL-AD7147 via J1 or J2, so that the ADUC841 can be used as an interface to the pc.

    For your system I would recommend this method, as it is not possible to interface these capacitors directly to the EVAL-AD7147 without modifying the board (cutting the existing traces and soldering them), this will not give a good connection or a reliable result.

  • Hi DarraghCorrigan,

    Your reply makes a lot more sense when I am looking at the board myself and play with it for a while. Thank you for your detailed answer. I am a rookie in analog circuits and it's starting to make sense for me now. Thank you!

  • 0
    •  Analog Employees 
    on Mar 25, 2014 9:29 PM

    Hi yin.padfoot, that's great, I'm glad I could help. Let me know if you have any more questions.

    Regards,
    Darragh