Sensor Configuration Options

Apart from kit configuration options as mentioned in the section above, each sensor's configuration can also be fine tuned editing different options.

This section explains the settings that are specific to each sensor. For example, sensor 0 can have a detect threshold (one of the sensor specific setting) that is different from sensor 1.

• Detect threshold

  A sensor’s negative (detect) threshold defines how much its signal must drop below its reference level to qualify as a potential touch detect. The final detection confirmation must however satisfy the Detect Integrator (DI) limit. Larger threshold values desensitize sensors since the signal must change more (i.e. requires larger touch) in order to exceed the threshold level. Conversely, lower threshold levels make sensors more sensitive.

  Threshold setting depends on the amount of signal swing that occurs when a sensor is touched. Thicker front panels or smaller electrodes usually have smaller signal swing on touch, thus require lower threshold levels.

  Table 1. Detect threshold

  Setting	Variable name	Data Type	Unit	Min	Max	Typical
  Threshold	threshold	uint8_t	counts	3	255	10-20

• Hysteresis

  This setting is sensor detection hysteresis value. It is expressed as a percentage of the sensor detection threshold setting. Once a sensor goes into detect its threshold level is reduced (by the hysteresis value) in order to avoid the sensor dither in and out of detect if the signal level is close to original threshold level.

  • Setting of 0 = 50% of detect threshold value (HYST_50)

  • Setting of 1 = 25% of detect threshold value (HYST_25)

  • Setting of 2 = 12.5% of detect threshold value (HYST_12_5)

  • Setting of 3 = 6.25% of detect threshold value (HYST_6_25)

    Table 2. Hysteresis

    Setting	Variable name	Data Type	Unit	Min	Max	Typical
    Hysteresis	detect_hysteresis	uint8_t (2 bits)	Enum	0	3	3

• Adjacent Key Suppression (AKS)

  In designs where the sensors are close together or set for high sensitivity, multiple sensors might report detect simultaneously if touch is near them. To allow applications to determine the intended single touch, the touch library provides the user the ability to configure a certain number of sensors in an AKS group.

  When a group of sensors are in the same AKS group, then only the first strongest sensor will report detection. The sensor reporting detection will continue to report detection even if another sensor’s delta becomes stronger. The sensor stays in detect until its delta falls below its detection threshold, and then if any more sensors in the AKS group are still in detect then the strongest will report detection. So at any given time only one sensor from each AKS group will be reported to be in detect.

  The library provides the ability to configure any sensor to be included in any one of the Adjacent Key Suppression Groups (AKS Group).

  Table 3. Adjacent Key Suppression (AKS)

  Setting	Variable name	Data Type	Unit	Min	Max	Typical
  AKS Group	aks_group	uint8_t (3 bits)	Enum	0 (off)	7	0 (off)