Datasheet

48 Document No. 001-66271 Rev. *B CY8C21x34/B CapSense
®
Design Guide
Figure 6-7. Flow Chart to Implement the Guard Sensor
Start of main function
End of main function
Initialize CapSense block and other blocks
Scan all sensors including Guard sensor
Update baseline of all sensors
Is Guard Sensor ON? Turn off all the sensors
Guard sensor
counter elapsed?
Report sensor status normally
Yes
No
No
Yes
6.2 Design Recommendations
The following system-level and PCB layout recommendations apply to CapSense systems that will be exposed to
water:
 Shield-electrode copper-hatch recommendations:
 Top layer – 7-mil trace and 45-mil grid (15-percent fill)
 Bottom layer – 7-mil trace and 70-mil grid (10-percent fill)
 The shield electrode between buttons should be at least 10 mm wide
 Only areas surrounding sensor pads and the CapSense controller should be grounded
 Place sensor surface vertically or at an angle to the horizontal so that water drops naturally move off the sensors
and large water drops do not accumulate.
 Use water-repellent and nonabsorbent overlay material. This minimizes water streaks and films on the device
panel. This is especially important if the water is highly conductive, such as seawater.
 You must use a guard sensor in situations where the application may be subjected to continuous water streams.
A guard sensor is not required if the device will be subjected only to rain.