Liquid-Tolerant Design Considerations
CY8C20xx7/S CapSense
®
Design Guide
Doc. No. 001-78329 Rev. *E
62
Figure 6-8. Capacitance Measurement with Large Liquid Spills or Water Stream
C
LD
- Capacitance between the water stream/liquid spill and shield electrode
C
ST
- Capacitance between the water stream/liquid spill and the system ground
C
WG
- Capacitance between the water stream/liquid spill and the guard sensor
The guard sensor should be implemented in firmware. One CapSense pin and a counter (hardware/software) are
required to implement the guard sensor.
When a water stream or a large liquid spill is present on the board, the guard sensor detects this event and disables
the touch sensor processing logic. Additional guard sensor "dead" time prevents unlocking the sensor prematurely.
When the liquid is gone, the guard counter suppresses touch processing for a short time (guard sensor counter). This
eliminates false touch detection from any water/liquid that remains on the board.
is a flow chart that shows how the guard sensor should be implemented in firmware.
