Insight into capacitive sensing parameters meaning

Hello Gianluca,

I would be happy to  help you these concepts.

Count - Think of a A/D converter, where a measured voltage is converted and quantized into measurement counts, N.

Example: 8-bit A/D using a 3v reference will convert a 1.5v input signal to a measurement of 128 counts.

CapTIvate is a capacitance to digital converter and works the same way, converting the measured capacitance into measurement counts.

LTA - CapTIvate is a relative measurement system.  This which means the system first performs a calibration on the sensor (when power is first applied) and feeds the resulting measurement count into a configurable beta IIR filter whose output is the LTA (long term average).  This LTA is used to provide a baseline or reference for subsequent measurement counts are compared to.

It's also important to note that in a perfect world the LTA should never change, but in the real world, environmental changes in temperature and humidity do affect the sensor's baseline capacitance.  This means the LTA will slowly go up or down, tracking these slow moving changes.

Delta - When the sensor experiences a rapid change in capacitance, like a finger touching the sensor, the count value will be higher or lower than the LTA and the difference is the delta.  The direction depends on if self or mutual capacitance method.  You can read more about those in the tech guide.

Touch threshold - This is a level (certain number of counts above or below the LTA) determined by the engineer during sensor tuning that when a finger touches the sensor, the delta is greater than this threshold and indicates a "touch" event in software.  Because of the environmental changes described above, you want this threshold to "track" with the LTA otherwise the system is useless across temperature.  So as the LTA goes up the touch threshold goes up too.  Make sense?