Cypress CY8C20xx7/S CapSense Series, Design Manual

Page: 59 / 75

Liquid-Tolerant Design Considerations
CY8C20xx7/S CapSense
®
Design Guide Doc. No. 001-78329 Rev. *E 59
Figure 6-2. Capacitance Measurement with Liquid Drop
C
LD
= Capacitance between the liquid drop and shield electrode
The purpose of the shield electrode is to set up an electric field around the touch sensors that helps attenuate the
effects of water. The shield electrode works by mirroring the voltage of the touch sensor on the shield.
Follow these guidelines to ensure proper shield operation:

Schematic

Layout

Firmware development
6.1.1.1 Schematic
Select the proper pin to drive the shield electrode out signal. The following pins should be used to drive the shield
electrode out signal.

Port pins: P0[0], P1[2], P0[2], P2[2], or P2[4]
6.1.1.2 Layout
Follow the layout guidelines given in Getting Started with CapSense.
6.1.1.3 Firmware Development
There is a shield drive GUI, as shown in Figure 6-3 , to minimize firmware development.
Figure 6-3. Driven Shield GUI (Shield Inactive)
Step 1: Enable the CapSense Shield Signal from the GUI.
Click on “Ebuf0”, which is the EnableShieldDriver switch, as shown in
Figure 6-4 ;
the “Disable” option is selected by
default. Select CapsenseShieldSignal to enable the shield driver.