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MSP430 Captivate Delta calculation

Hi,

With respect to the MSP430 Captivate design, the Users Guide
don't have details of some parameters like Delta.
Could you please let us know how if there is any equation to find out delta.

Can we use below equation from previous Capacitive guide?

delta = base - measurement

The config.c has definition for sensorpad as shown below,
but we couldn't understand how the Delta and Base values are calculated
in this function.
u
// Sensor: keypadSensor, Element: E00
uint16_t keypadSensor_E00_RawCnts[CAPT_SELF_FREQ_CNT];
tCaptivateElementTuning keypadSensor_E00_Tuning[CAPT_SELF_FREQ_CNT];
tElement keypadSensor_E00 =
{
    .ui8RxPin = 0,
    .ui8RxBlock = 0,
    .ui8TouchThreshold = 10,
    .pRawCount = keypadSensor_E00_RawCnts,
    .pTuning = keypadSensor_E00_Tuning,
};


Please let us know if there is more details on Delta and Base calculations.

Best Regards
Kummi

  • Dear Kummi,
    Thank you for the feedback regarding the documentation. I will submit a request to update the documentation per your comments. The delta is the difference between the filtered count (software-dl.ti.com/.../ch_Glossary.html and the long term average (software-dl.ti.com/.../ch_Glossary.html.

    There are two thresholds, a proximity threshold (software-dl.ti.com/.../ch_Glossary.html which is defined in the sensor and a touch threshold (software-dl.ti.com/.../ch_Glossary.html which is defined in the element structure.

    Fundamentally the CapTIvate solution is still a relative solution, but the CapTIvate has significantly more HW and SW features. If you look in CAPT_Type.h you will find the structure definition of the element where the filter count and LTA reside.

    Thanks and Regards,
    Chris
  • Hi Chris,

    With regards to the delta calculation,
    we are trying to access the filtered count and the long term average(LTA)
    with the TI's sample code, but we don't understand how to do it.

    Could you please let me know how to access these raw data(filtered count & LTA) in the sample code?

    Best Regards
    Kummi

  • Kummi,
    The LTA and filtered count are part of the element definition (tElement) and are not made available in the examples to the main.c file. If you want to add them, then add the appropriate 'extern' to the element prototypes. You will find the sensor definitions there already. For example " extern tElement keypadSensor_E00"

    Alternatevely you can access the data via the sensor structure. But this requires you know the cycle and element count. For example "keypadSensor->pCycle[0]->pElements[0]->filterCount" points to the first element in the first cycle of the keypadSensor.

    The same can be done for the LTA.

    Regards,
    Chris

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