Key facts
- Brand
- STMicroelectronics
- Model
- AN2927
- Industry
- Industrial
- Documents
- 2
- Languages
- EN
- Last added
- 2012-08-07
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STMicroelectronics AN2927 RC Acquisition Principle Application Note
This document explains the RC acquisition principle used to detect human touch in capacitive touch-sensitive controls. It details how the method measures small variations in electrode capacitance by charging and discharging a network formed by a resistor and the touch electrode. The note covers the underlying physics, the hardware implementation using a single resistor, and the firmware implementation within the ST touch sensing library.
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How to use the product for one specific task, with worked examples.
Questions answered in these manuals
What is the typical capacitance variation caused by a human finger touching an electrode?
The capacitance variation is typically a few picofarads, specifically around 5pF.
From: STMicroelectronics AN2927 RC Acquisition Principle Application Note
How many successive measurements are required for STM8 microcontrollers to span all possible input voltage values?
Eight successive measurements are necessary to span all the possible values.
From: STMicroelectronics AN2927 RC Acquisition Principle Application Note
How does the RC acquisition method detect human touch?
It detects human touch by measuring the small variation of the touch electrode capacitance (C) caused by a finger, which changes the charge time of an RC network.
From: AN2927 RC Acquisition Principle for Touch Sensing Applications Application Note
How many resistors are needed per touch channel?
Only one resistor is needed per touch channel to enable this function.
From: AN2927 RC Acquisition Principle for Touch Sensing Applications Application Note