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Design Guide for Capacitive Sensing Sliders & Wheels

Chad Kidder
Intellectual 455 points

After dredging through the TI document library and here on e2e, I have to ask, where is the design guide/examples for implementing captouch sliders and wheels on a PCB?  There are guidelines for a single button (space between the button and ground 1/20th of the radius of the button) but I don't see any for sliders or wheels.  Since there is a board available for the Launchpad to demonstrate this, I assume there is one out there.  The shapes on the add-on board for the LaunchPad (430BOOST-SENSE1) are not intuitively obvious.  Did I just miss a tech note somewhere?

  • 0
    TI__Genius 9990 points

    Chad,

    One source on this is described here:

    http://focus.ti.com/lit/an/slaa363a/slaa363a.pdf

     

    The new Experimenter board using F5529 implements cap touch and they work very nicely. It's not completely out yet but hopefully will be soon:

    http://focus.ti.com/docs/toolsw/folders/print/msp-exp430f5529.html?DCMP=OTC-MCU_Newsflash&HQS=Other+NL+mcunf-march11-msp430-tf2

     

    Gustavo

  • 0 in reply to Gustavo L
    Intellectual 455 points

    Gustavo,

     

    slaa363a is where I got the 1/20th design guideline from.  It does not address scroll wheels at all and does not address any differences in PCB layout between a slider and multiple buttons (other than ground).  Looking at both the documentation for the 430BOOST-SENSE1 one can easily see that the inter-button spacing is tighter than button to ground.  Nothing is mentioned about that in its documentation or slaa363a.  If I had to cut a PCB with a scroll wheel today I'd either take the GERBERs from the 430BOOST-SENSE1 and copy that or try to apply someone else's design guide.  I'm surprised that there isn't more out there on this topic, with as well documented as TI products tend to be... or is capacitive sensing something that TI has only recently gotten serious about?  I didn't even realize you could do it with a MSP430 until I had worked with them for over a year and I had a TI employee correct me when I said something.

  • 0 in reply to Chad Kidder
    TI__Genius 9990 points

    Chad,

    For the 430Boost I'd be very careful. If you touch the sides (the black connectors) you will create some capacitance and it will give some erroneous readings Otherwise, if integrated into a PCB it should work.

     

    Gustavo

  • 0 in reply to Gustavo L
    Intellectual 455 points

    SLAA490, the Capsense Library Programmer's guide provides a bit more detail on how to lay things out.  There is supposed to be a SLAA491, Getting Started with  the Capsense library, according to the TI press release, but the given link does not link to anything at this time.  Do any of the TIers out there know when a more comprehensive PCB layout design guide for capsense will be released?

  • 0 in reply to Chad Kidder
    TI__Prodigy 450 points

    Please visit the following link to access the Getting Started With Capacitive Touch Software Library (SLAA491): http://www.ti.com/litv/pdf/slaa491

    Regret any inconvenience for the broken link.

    Thanks,
    Abhi

  • 0 in reply to Abhi99
    Intellectual 455 points

    Sorry, that doesn't answer my question either.  It gives an example of physical layout, but no guidelines for actually implementing it.

  • 0 in reply to Chad Kidder
    Expert 1535 points

    You can search in SLAA576.

    I hope is not too late.

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