CAP1214 Datasheet, PDF (26/107 Pages) SMSC Corporation – Multiple Channel Capacitive Touch Sensor and LED Driver

Multiple Channel Capacitive Touch Sensor and LED Driver
Datasheet
5.4 Capacitive Touch Sensing
The CAP1214 contains 14 independent Capacitive Touch Sensor inputs. Each sensor input detects a
change of capacitance due to a touch. Additionally, each sensor can be configured to be automatically
and routinely re-calibrated.
5.4.1 Multiple Button Presses
If multiple sensor buttons (with a programmable threshold - see Section 6.23) are simultaneously
detected, only the first N buttons that are detected are flagged. All other buttons are ignored.
Furthermore, the device remembers which buttons were legitimate so new touches are not detected
so long as N buttons are pressed.
Likewise, if too many (based on the programmed threshold - see Section 6.23) grouped sensor
presses are detected, the device will block all press detections on the grouped buttons and cancel any
current presses as if the sensor had been released.
5.4.2 Lid Closure
To detect lid closure or other similar events, lid closure sensor thresholds can be set. A Lid Closure
Event can be flagged based on either a minimum number of sensors or on specific sensors
simultaneously exceeding the lid closure threshold. An interrupt can also be generated. During a Lid
Closure Event, all touches are blocked.
5.4.3 Grouped Sensors (CS8 - CS14)
Capacitive Touch Sensors 8 through 14 may be grouped as a single entity (which is the default state).
Each sensor is sampled independently; however, for purposes of activation, recalibration, and repeat
rates, all of them are treated as one group. The Group also has different controls and allows for
different behavior such as sliding, tapping, or press and hold.
The grouped sensors may be ungrouped as described in Section 5.6.
5.4.4 Sensing Cycle
Each Capacitive Touch Sensor has controls to be activated and included in the sensing cycle. When
the device is active, it automatically initiates a sensing cycle and repeats the cycle every time it
finishes. The cycle polls through each active Sensor starting with CS1 and extending through CS14.
As each Capacitive Touch Sensor is polled, its measurement is compared against a baseline “Not
Touched” measurement. If the delta measurement is large enough, a touch is detected and an interrupt
generated.
5.4.5 Proximity Detection
Sensor CS1 can be configured to detect changes in capacitance due to proximity of a touch. This
circuitry detects the change of capacitance that is generated as an object approaches, but does not
physically touch, the CS1 sensor. When proximity detection is enabled, the signal is boosted by 8x to
detect very small capacitance changes. Separate controls determine averaging and sensitivity for
proximity (see Section 6.35, "Proximity Control Register").
5.4.6 Recalibrating Sensors
Each sensor is regularly recalibrated at a programmable rate. By default, the recalibration routine
stores the average 256 previous measurements and periodically updates the base “Not Touched”
setting for the Capacitive Touch Sensor input. This routine is disabled automatically if a touch is
detected so the touch does not factor into the base “Not Touched” setting.
Revision 1.0 (08-30-10)
26
DATASHEET
SMSC CAP1214