5 and 6 Channel Capacitive Touch Sensor
Datasheet
4.2
Capacitive Touch Sensing
The CAP1005 / CAP1006 contains six (6) (CAP1006) or five (5) (CAP1005) independent Capacitive
Touch Sensor inputs. Each sensor has dynamic range to detect a change of capacitance due to a
touch. Additionally, each sensor can be configured to be automatically and routinely re-calibrated.
4.2.1
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 CS6. As
each Capacitive Touch Sensor is polled, its measurement is compared against a baseline “not touched”
measurement. If the delta measurement is large enough, then a touch is detected and an interrupt
generated.
The sensing cycle time is programmable (see Section 5.10).
4.2.2
Recalibrating Sensors
Each sensor is regularly recalibrated at an adjustable 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.
It is possible that the device loses sensitivity to a touch. This may happen as a result of a noisy
environment, an accidental recalibration during a touch, or other environmental changes. When this
occurs, then the base untouched sensor may generate negative delta count values. The device will
detect this condition based on a programmable number of consecutive negative delta readings. When
it detects the condition, the CAP1005 / CAP1006 will automatically re-calibrate the base-count settings.
During this recalibration, the device will not respond to touches.
4.3
ALERT# Pin
The ALERT# pin is an active low output that is driven when an interrupt event is detected.
Whenever an interrupt is generated, the INT bit (see Section 5.1) is set. The ALERT# pin is cleared
when INT bit is cleared by the user. Additionally, when the INT bit is cleared by the user, status bits
are only cleared if no touch is detected.
4.3.1
Sensor Interrupt Behavior
The sensor interrupts are generated in one of two ways:
1. An interrupt is generated when a touch is detected and when a release is detected (see Figure 4.4).
2. If the repeat rate is enabled (see Section 5.6), then, so long as the touch is held, another interrupt
will be generated based on the programmed repeat rate (see Figure 4.3).
When the repeat rate is enabled, the device uses an additional control called MPRESS that determines
whether a touch is flagged as a simple “touch” or a “press and hold”. The MPRESS[3:0] bits set a
minimum press timer. When the button is touched the timer begins. If the sensor is released before
the minimum press timer expires, then it is flagged as a touch and an interrupt is generated upon the
release. If the sensor detects a touch for longer than this timer value, then it is flagged as a “press
and hold” event. So long as the touch is held, interrupts will be generated at the programmed repeat
rate and upon a release.
SMSC CAP1005 / CAP1006
Revision 1.1 (08-05-09)
DATA2S5HEET
SMSC [ SMSC CORPORATION ]
