May 2013

DocID17048 Rev 3

1/25

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

Table 1. Applicable products

Type

Applicable products

Microcontrollers

STM8T141, STM8T143

www.st.com