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MSP430FR2633: Minimum electrode size of button using CapTIvate

U-SK
Genius 5840 points
Part Number: MSP430FR2633

Hello.

I would like to use CapTIvate powered by battery.

I would like to know the number of buttons and the minimum size that can be implemented when powering by battery because the board size is limited to 80 x 80 mm.

Could you give me something advice about this?

 

According following document, buttery application reduce sensitivity of CapTIvate.

http://software-dl.ti.com/msp430/msp430_public_sw/mcu/msp430/CapTIvate_Design_Center/latest/exports/docs/users_guide/html/CapTIvate_Technology_Guide_html/markdown/ch_design_guide.html

Regards,

U-SK

  • 0
    TI__Guru 68011 points

    Hello U-SK,

    You are correct.  Operating on battery can significantly reduce a sensor's sensitivity.

    For non-battery powered applications the recommended button size ranges from 8-12mm (10mm typical).  For battery powered applications you may consider increasing this by 50% if it is a self capacitive sensor.  This means a 10mm typical size button for battery application could be 15mm.  With self capacitive buttons you will have to be careful of nearby grounds, such as ground planes on the PCB, as these will greatly reduce the self capactive sensor's sensitivity.

    For mutual capacitive buttons (typical for keypads) you should be able to use 12mm.  Mutual sensing relies less on the coupling to ground (as does self capacitive sensor) and more on the coupling between the sensor's RX and TX electrodes.  This means a mutual capacitive sensor will have somewhat better sensitivity for the battery powered application.

    To determine the number of buttons that can be placed within the 80mm2 area you should have at a minimum the width of one finger spacing between buttons to prevent cross coupling of touch signals from neighboring buttons.  So for example using 12mm mutual capacitive buttons and 12mm spacing between buttons it looks like you can get about 9 buttons.

    As a closing comment a very important recommendation when designing a battery powered device is to prototype and test the design to ensure you get the expected performance.

  • 0 in reply to Dennis Lehman
    TI__Guru 68011 points

    Hello U-SK,

    I haven’t heard from you for a couple of days now, so I’m assuming you were able to move forward with your design.
    If this isn’t the case, please click the "This did NOT resolve my issue" button and reply to this thread with more information.
    If this thread locks, please click the "Ask a related question" button and in the new thread describe the current status of your issue and any additional details you may have to assist us in helping to solve your issues.

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