Cypress CapSense CY8C20x36 Betriebsanweisung PDF herunterladen (Seite 31)

Getting Started with CapSense

Document No. 001-64846 Rev. *I 31

2.8 Water Tolerance

Capacitive touch sensing is effective in applications where the touch sensing zone is exposed to moisture, rain, or

water drops. Such applications include automotive applications, outdoor equipment, ATMs, public access systems,

and portable devices such as cell phones, PDAs, and kitchen and bathroom applications. Two common triggers are

water droplets on sensors and the flow of water on the PCB. Shield electrodes and guard sensors (see Shield

Electrode and Guard Sensor for layout) help in achieving a water-tolerant capacitive sensing design. For more

information on the working of guard sensors and shield electrodes, see the CY8C21x34 Design Guide.

 Water droplets: Use a shield electrode to prevent false triggering of buttons due to water droplets. Device

operation is guaranteed (sensors respond to finger touch) in case of water droplets.

 Water stream: Use a shield electrode and guard sensor to prevent sensors from being triggered because of

water streams. Sensors do not respond to finger touch in the presence of water streams; only false triggering is

prevented.

2.9 CapSense System Overview

CapSense touch sensing solutions include the entire system environment in which they operate. This includes:

 Hardware component, such as PCB and guard sensor

 Firmware component to process the sensor data

2.9.1 Hardware Component

The CapSense controller resides within a larger system composed of a specially printed circuit board (PCB), and a

touch-surface called the overlay that protects the PCB.

Figure 2-32. Exploded View of the CapSense Hardware

The capacitive sensor pads of a sensor board are formed by the PCB traces. The most common PCB format is a two-

layer board with sensor pads and a hatched ground plane on the top, and the electrical components on the bottom.

The electrical components include the CapSense controller and associated parts that convert the sensor capacitance

into digital counts. Figure 2-33 shows a cross-sectional view of a two-layer board stack-up.

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Cypress CapSense CY8C20x36 Betriebsanweisung Seite 31