SX8635I05AWLTRT SEMTECH [Semtech Corporation], SX8635I05AWLTRT Datasheet - Page 15

• Manufacturer Part Number: SX8635I05AWLTRT
• Description: Low Power, Capacitive Button and Wheel Touch Controller with Enhanced LED
• Manufacturer: SEMTECH [Semtech Corporation]

ADVANCED COMMUNICATIONS & SENSING
3.6 Button and Wheel Information
3.6.1
The touch buttons have two simple states (see Figure 11): ON (touched by finger) and OFF (released and no
finger press).
A finger is detected as soon as the number of ticks from the ASI reaches a user-defined threshold plus a
hysteresis.
A release is detected if the ticks from the ASI go below the threshold minus a hysteresis. The hysteresis around
the threshold avoids rapid touch and release signaling during transients.
Buttons can also be used to do proximity sensing. The principle of proximity sensing operation is exactly the same
as for touch buttons except that proximity sensing is done several centimeters above the overlay through the air.
ON state means that finger/hand is detected by the sensor and OFF state means the finger/hand is far from the
sensor.
3.6.2
In case sensors are arranged in a wheel configuration the ON, OFF information remains available as if it would be
a single sensor button.
Wherever the wheel is touched the information will be set to ON. If no finger is present the wheel information will
be OFF.
Due to the 2 dimensional character of the wheel more information can be derived by processing the ticks.
During a touch a finger will influence most of the time the charge on one or two sensors but never all of the
sensors at the same time. Some sensor ticks will be larger than others based on the finger position.
The processing algorithms can therefore determine where the finger is positioned on the wheel.
Interpolation between sensors increases the resolution beyond the number of sensors in the wheel.
The interpolation can be done already on the PCB sensor structures (analog, like the wheel in Figure 10) and as
well by SX8635 digital processing of the ticks using center of gravity calculations.
The position of the finger on the PCB structures varies between the minimum zero and a user defined maximum
(Figure 13).
Revision 7_8, October 10
Button Information
Wheel Information
(12 sensors) with Enhanced LED Drivers and Proximity Sensing
Figure 12
© 2010 Semtech Corp.
Low Power, Capacitive Button and Wheel Touch Controller
Figure 11
Wheel ON, OFF
15
Buttons
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SX8635