Best-in-Class Detection Range of up to 25 cm

Capacitive touch-sensing is by definition proximity detection. For standard buttons, the thickness of the overlay is the proximity setting. The sensor response is highest when a finger is pressing on the overlay. In true proximity sensing, no contact is required between the sensor overlay and the user's finger or hand. In this application, it is necessary to increase the sensitivity of the sensor over that required for buttons. Increased sensitivity is realized by acquiring data from the sensor for a greater time. Longer acquisition times allow very small changes in capacitance that arise from more distant conductive objects to be magnified.

Obviously, when the acquisition time is increased for such applications, the update rate is slower. However, proximity detection applications require that sensors only detect presence, not fine, rapid movements. Therefore, it is possible to detect conductive objects over greater distances while achieving the kind of update rate and response time that proximity sensing requires.

There are also some changes that can occur in hardware to increase the sensitivity of a proximity sensing apparatus. Larger sensors have greater sensitivity to larger conductive objects, such as a hand. Removing the ground plane from the underside of the sensor PCB increases the sensitivity, but allows the field lines to direct themselves toward the user, rather than toward a ground plane. Increasing the space between the sensor and the surrounding ground plane also directs field lines toward the user.  

For more information:

30-minute interactive video on how to design CapSense Proximity sensing using the CY3270 PSoC FirstTouch Starter Kit.  The video also showcases the best-in-class detection range of 25 cm.  Go to support > online courses and select "Building a Proximity Detector Using PSoC Designer".

Application Note: Proximity Detection in the Presence of Metal Object - AN42851.