CY8C20xx7/S CapSense
®
Design Guide
Doc. No. 001-78329 Rev. *E
64
7. Proximity Sensing Design Considerations
Proximity sensors detect the presence of a hand or other conductive object before it makes contact with the
capacitive touch surface. Imagine a hand stretched out to operate a car audio system in the dark. Proximity detection
enables the system to light up with the approach of a finger. For example, the buttons of an audio system will glow
with its backlight LEDs when the user's hand is near.
7.1 Types of Proximity Sensors
7.1.1 Button
A button with large C
P
and small difference counts can work as a proximity sensor. The sensitivity of a proximity
sensor implemented as a button is much higher than a regular capacitive touch-sensing button.
7.1.2 Wire
A single length of wire works well as a proximity sensor. Because detecting a hand relies on the capacitance change
from electric field changes, any stray capacitance or objects affecting the electrical field around the wire will affect the
range of the proximity sensor. Using a wire sensor is not an optimal solution for mass production because of
manufacturing cost and complexity.
7.1.3 PCB Trace
A long PCB trace can form a proximity sensor. The trace can be a straight line, or it can surround the perimeter of a
system‟s user interface, as shown in
. This method is appropriate for mass production, but it is not as
sensitive as a wire sensor.
Figure 7-1. Proximity Sensor Using PCB Trace
7.1.4 Sensor Ganging
Another way to implement a proximity sensor is to gang sensors together. This is accomplished by combining
multiple sensors into one large sensor, using firmware to connect the sensors from the internal analog multiplexer
bus in PSoC Designer. Be careful not to exceed the C
P
limit of your design when using this method.
Proximity Sensor
