Application note

How to design surface sensors for touch sensing applications on STM32 MCUs

Rev 10 - February 2025

Introduction

This document describes the layout and mechanical design guidelines used for touch sensing applications with surface sensors.

Capacitive sensing interfaces provide many advantages compared to mechanical user interfaces: modern look and feel, easy to clean, waterproof and robust.

Capacitive sensing interfaces are used in a wide range of applications. The interface is based on surface sensors made of small copper foils. The sensor acts as a capacitor that is alternatively charged and discharged. The capacitor value depends on the presence of the user's finger, as well as the sensor design. This application note introduces various sensor designs and recommendations to achieve optimum performance, keeping in mind that none of the sensor elements must interfere with each other.

This document provides guidelines on printed circuit board (PCB), overlay and panel materials plus all other items in the capacitive sensor environment.

Table 1. Applicable products
TypeProducts series
Microcontrollers
  • STM32F0 series, STM32F3 series
  • STM32L0 series, STM32L1 series, STM32L4 series, STM32L4+ series, STM32L5 series
  • STM32U0 series, STM32U3 series, STM32U5 series
  • STM32WB series, STM32WBA series

Capacitive sensing technology

STMicroelectronics offers different capacitive sensing technologies for Arm-based STM32 microcontrollers.

The technology covered by this application note is based on the charge transfer acquisition principle and is supported by all microcontrollers listed in Table 1.

Note: Arm is a registered trademark of Arm Limited (or its subsidiaries) in the US and/or elsewhere.