User guide

20 Document No. 001-64846 Rev. *A Getting Started with CapSense®
Features of a design based on springs/gaskets/foam:
 Electrical field coupled from PCB to overlay using a compressed spring, or conductive gasket or foam
 Conductive material itself acts as capacitive sensor pad
 No mechanical moving parts. Springs and foam do not move
 Coupled to touch sensor surface via nonconductive overlay
 Any conductive overlay serves as the button touch surface
 Ideal topology for curved, sloping or otherwise irregular front panels
 Ideal for designs where touch sensor surface is physically separated from silicon or mother board
 Ideal for designs where CapSense and mechanical button combination is desired
2.6.3 Field Coupled via Printed Ink
Features of a design based on printed ink:
 Electric field coupled with printed patterns on a flexible substrate using conductive ink
 High series resistance due to higher ohms-per-square of printed ink compared to copper
 High parasitic capacitance due to thin PCB
 No mechanical moving parts, but substrate is flexible
 Coupled to touch sensor surface with a nonconductive overlay
 Ideal topology for flexible front panels
 Flexible PCB can be one-layer or two-layer film
2.6.4 Field Coupled via ITO Film on Glass
Features of a design based on ITO film:
 Electric field coupled with printed or deposited patterns on glass
 Higher series resistance of ITO films compared to copper and printed ink
 No mechanical moving parts
 Ideal topology for graphical front panels
2.7 CapSense Feedback
Effective user interface designs include some type of feedback to the user when they are using the capacitive touch
sense buttons. There are various forms of feedback, including visual, audio, and haptic (tactile). Depending on the
user interface design multiple types of feedback can be used in combination.
2.7.1 Visual Feedback
LEDs and LCDs provide visual feedback to the user.
2.7.1.1 LED-based Visual Feedback
LEDs are used to indicate the status of buttons, sliders, and proximity sensors. LEDs can implement different effects
when the sensor status changes.
2.7.1.1.1 LED ON/OFF
In visual feedback’s simplest form, LEDs are turned ON or OFF in response to a finger touch. General-purpose I/Os
are used to drive LEDs in either a sourcing or sinking configuration, as shown in Figure 2-20 on page 21.