STMicroelectronics AN2869 Capacitive Sensing Application Guidelines

About this manual

This document outlines the layout and mechanical design guidelines necessary for developing touch sensing applications. It covers three main aspects: Printed Circuit Board (PCB) design, overlay and panel materials, and environmental factors that may interfere with sensor performance.

The note details four specific acquisition principles available in STMicroelectronics product families: RC acquisition, charge transfer acquisition, surface ProxSense™ acquisition, and projected ProxSense™ acquisition. It provides specific recommendations for designing surface electrodes (touchkeys, linear, rotary) and projected sensors.

What's inside

• Capacitive sensing technology
• RC acquisition principle
• Charge transfer acquisition principle
• Surface ProxSense acquisition principle
• Projected ProxSense acquisition principle
• Main capacitive sensing guidelines
• PCB and layout considerations
• Panel materials selection
• LED placement near sensors
• Power supply requirements

Frequently asked questions

Which microcontroller families are applicable to this application note?

The note applies to STM8A, STM8S, STM8L, STM8T14x, STM8TL5x, and various STM32 FO and L1 series microcontrollers.

What microcontrollers are applicable for this application note?

The document lists STMBA automotive, STMBL ultra-low-power, STM8S mainstream, STME8T touch-sensing, and STM32 FO entry-level Cortex-M0 or L1 ultra-low-power ARM Cortex-M3 based microcontrollers as applicable products.

What are the advantages of capacitive sensing interfaces compared to mechanical ones?

Capacitive sensing interfaces offer a modern look and feel, are easy to clean, waterproof, and robust.

What is the main difficulty in designing capacitive sensing interfaces?

The main difficulty is ensuring that none of the items interfere with each other.