CapSense Technology
AN64846 - Getting Started with CapSense
®
Doc. No. 001-64846 Rev. *X
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Figure 2-45. Proximity Sensing Based on CapSense in a Soap Dispenser
2.9.2 Proximity Sensing with CapSense
The proximity-sensing technique based on CapSense involves measuring the change in capacitance of a proximity
sensor when a target object approaches the sensor. The target object can be a human finger, hand, or any conductive
object. Proximity sensors can be constructed using a conductive (usually copper or indium tin oxide) pad or trace laid
on a nonconductive material like PCB or glass. In essence, a proximity sensor is like any other sensor but designed
with very minimum ground near the sensor and tuned for maximum sensitivity.
For detecting the target object, the
should be greater than or equal to 5:1. Therefore, you
can detect the proximity of the target object without error up to a certain distance from the sensor. This distance is
called the proximity-sensing distance. Refer to
to learn the various ways of constructing a
proximity sensor and to learn the various parameters that affect the proximity distance.
2.10 User Interface Feedback
Effective user interface designs include feedback to the user when they are using the capacitive touch sense buttons.
There are various forms of feedback, including visual, audio, and haptic (tactile). Depending on the user interface
design, multiple types of feedback can be used in combination.
2.10.1 Visual Feedback
LEDs and LCDs provide visual feedback.
2.10.1.1 LED-Based Visual Feedback
Visual feedback is widely used in user interfaces. LEDs are used to indicate the status of buttons, sliders, and proximity
sensors. LEDs can implement different effects when the sensor status changes as listed below.
LED ON/OFF
– GPOs are used to drive LEDs in either a sourcing (GPO supplies current to the LED) or sinking
(GPO sinks current from the LED) configuration.
LED Brightness Control - For user interfaces that require sophisticated visual effects, a single hardware PWM or
timer can be used to drive the LEDs. By varying the duty cycle of the PWM output, you can adjust the LED
brightness. This enables adjusting your user interface brightness in response to ambient lighting conditions.
LED Fading - By gradually changing the duty cycle between LED states, you can achieve a fading effect. For
example, t
he LED appears to “fade in” (from OFF to ON) when the duty cycle is increased in a series of small
steps.
LED Breathing - Gradually increasing and decreasing the duty cycle between two levels on a continuous basis
makes the LED appear to “breathe”. LED breathing is useful when a system is in idle or stand-by mode. For
example, a power button can appear to breathe to alert the user that it is active and can be operated.
2.10.1.2 LCD-Based Visual Feedback
LCDs provide visual feedback for CapSense buttons and sliders. The main advantage of using an LCD is that it can
provide more information along with the feedback for each button press event. Depending on the device family,
