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MSP430: Using Cap touch to trigger start up

Alyssa Chatten
Prodigy 275 points

Hi E2E,


I am working on an application using cap touch with the MSP430. My system requires very low power and the MSP430 will be in standby mode a majority of the time. I would like to use the cap sensor to trigger the MSP430 out of standby. Is this a feasible solution and how would you recommend implementation?


Thank you,


Alyssa Chatten

  • 0
    Guru 58965 points

    It is possible to do so. But the power consumption may not be very low.

  • 0 in reply to old_cow_yellow
    TI__Prodigy 275 points

    A quick follow up question: How would you recommend implementation for this application? How much power would it consume?

    Thanks,

    Alyssa Chatten

  • 0 in reply to old_cow_yellow
    Guru 227245 points

    I don’t think it is possible to have a CapTOuch sensor directly wakin the MSP from LPM. CapTouch works with measuring the oscillation frequency. Then the frequency is compared to a reference by the code, deciding whether it is a touch or not. There is no hardware frequency check that could generate a waking interrupt. You would need an external frequency filter that detects the change of the oscillation frequency due to the touch and triggers a normal port pin interrupt.
    However, OCY is correct: this will be quite energy-consuming. Having the oscillator on all the time will likely consume more than waking form LPM by a timer every now and then and do a CapTouch check with active CPU. Not to mention the external hardware.

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