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MSP430FR2633: Configure pin for shield electrode

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Replies: 2

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Part Number: MSP430FR2633

Hi,

I'm trying to create a proximity sensor and have been looking at the reference design, CAPTIVATE-PROXIMITY, described in the MSP-CAPT-FR2633 Development Kit documentation. https://www.farnell.com/datasheets/2003068.pdf

Especially, I'm trying to figure out how to configure the CAP1.3 in this text:
"The module's 4 electrodes are connected to CAP0.3, CAP1.3, CAP2.3, and CAP3.3. CAP1.3 is used for the shield electrode, which is a solid plane across the bottom layer of the PCB and a ring around the 3 zones on the top layer of the PCB"

Would be very thankful for any guidance for how to do that. 

Kind Regards,
Grigory

  • Hello Grigory,

    It's simple.  The proximity sensor is configured as a 4-button sensor. CAP0.3, CAP2.3 and CAP3.3 are the channels of interest and CAP1.3 is the guard channel.

    What this means is when the sensor is scanned, all 4 channels are measured.  In a user's callback function you would look at the readings of the 3 channels of interest to determine if there is a proximity and what you want to do.  The guard channel you don't do anything with.  It's purpose is only to drive the shield on the backside of the PCB to the same potential as the 3 channels of interest, thereby isolating those channels from the ground parasitics caused by the table, or whatever, the PCB is sitting on.

    That proximity PCB in the pdf has been obsoleted and the example code for it is no longer available.  However, I have a copy from back then and will post here.  The zip contains the MSP430 source code as well as the Captivate Design Center project.  Note, if you open this project in a recent (newer) version of the design center you will see a message saying the project is old. You can ignore that if you just want to take a look at the settings.  If you have this PCB and want to program your target and communicate with the design center, then yes, you will need to create a new project in your version of design center.

    This may help you see how it all works.

    CAPTIVATE-PROXIMITY.zip

    Dennis Lehman

  • In reply to Dennis Lehman:

    Hi Dennis

    Thanks a lot for so quick and detail reply. It's very helpful. I'm using my own PCB, but it's pretty clear how I should configure it.

    Kind Regards,
    Grigory

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