AN3150 Datasheet, PDF (1/25 Pages) Freescale Semiconductor, Inc – Soldering Recommendations for Pressure Sensor Devices

AN3150
Application note
Guidelines to optimize proximity detection
with STM8T141 and STM8T143 capacitive sensors
Introduction
The STM8T14x capacitive sensors open up a new dimension in capacitive sensing by
detecting user proximity up to a few centimeters. This is a key feature for many end-
applications such as personal navigation devices (PNDs) or stove tops which are equipped
with backlighting that switches on as soon as a user is detected. Proximity detectors are
also implemented in white goods, automotive devices, palm tops, and on any type of kitchen
or office appliance where the display needs to be turned on to allow some parameters to be
adjusted by the user.
To enhance their application appearance and ease-of-use, designers can choose to add
proximity detection as an extra feature. Another motivation to add a proximity detection, in
particular for portable devices, is energy saving. The product usually remains in sleep mode
and only wakes up when it detects a user in its proximity.
One of the key features of capacitive sensors versus conventional proximity detectors (such
as infrared light sensors), is the low power scheme. Capacitive sensors consumption is in
the range of µA, versus mA for conventional sensors. Such a low power scheme is a
fundamental characteristic for power sensitive applications.
The phenomenons described in this document exist in all capacitive sensing
implementations. Because of the high sensitivity required by proximity detection, their
impact seems amplified compared to touch sensors and therefore must be considered with
great care.
A set of tools are provided to develop touch sensing applications based on STM8T141 and
STM8T143. This includes :
• Hardware tools: STM8T141-EVAL, ST8T143-EVAL, ST-TSLINK, STM8T14X-SB
• PC application: STM-STUDIO, STVP
Type
Microcontrollers
Table 1. Applicable products
Applicable products
STM8T141, STM8T143
May 2013
DocID17048 Rev 3
1/25
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