CapSense Technology
AN64846 - Getting Started with CapSense
®
Doc. No. 001-64846 Rev. *X
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3. Tune the guard sensor (if implemented) such that it is triggered only when there is a liquid stream. In the firmware,
ensure that the sensors are not scanned when the guard sensor is triggered.
Refer to the individual CapSense design guides for detailed procedures of how to tune the CapSense parameters to
achieve liquid tolerance. The application note,
– Proximity Sensing with CapSense
, shows how to implement
a proximity-sensing system with liquid tolerance for PSoC 4 devices.
2.9 Proximity Sensing
Proximity sensing is the process of detecting a nearby object without any physical contact. Proximity sensors use an
electromagnetic field, beam of electromagnetic radiation, or changes in ambient conditions to detect the proximity of a
nearby object. There are various types of proximity sensors such as capacitive, inductive, and magnetic, Hall effect,
optical, and ultrasonic sensors; each has its own advantages and disadvantages. Capacitive proximity sensing has
gained huge popularity because of its low cost, high reliability, low power, sleek aesthetics, and seamless integration
with existing user interfaces. This section presents an introduction to CapSense-based proximity sensing. Refer to
– Proximity Sensing with CapSense
for the complete proximity design guidelines.
2.9.1 Proximity-Sensing Applications Based on CapSense
Proximity sensing based on CapSense is used in a variety of applications as explained below.
Face detection in mobile phones and tablets:
Face detection is a feature in mobile phones that disables the phone’s
touchscreen and dims the brightness of the display when a user answers a phone call, as
detection prevents false touches when the phone is placed on the ear and optimizes the device’s power consumption.
Using proximity sensing based on CapSense in this application offers advantages over IR proximity sensing because
it does not require cutouts in the overlay material, which reduces the tooling cost and improves the aesthetics of the
end product.
Figure 2-41. Face Detection in Mobile Phones
SAR regulation in tablets and mobile phones:
SAR is a measure of the rate at which energy is absorbed by the
human body when exposed to an RF electromagnetic field. Regulatory bodies, such as the Federal Communications
Commission (FCC), require devices to limit the absorption of RF energy by reducing the
device’s RF transmit power
when the device is in close proximity to the human body, as
shows. Proximity sensors based on CapSense
can be used to detect the proximity of the human body and reduce RF power.
Figure 2-42. SAR Regulation in Tablets
Wake-on-approach:
This feature activates the system from the sleep or standby mode when an object approaches
shows. Wake-on-approach is also used to control the backlight LEDs when the user
approaches the system. This feature reduces system wakeup time, improves device responsiveness, reduces device
power consumption, and improves aesthetics. It is useful in battery-operated applications such as mice and keyboards.
Figure 2-43. Wake-on-Approach Implemented in a Mouse
