This application guide explains how to design an RC‑type capacitive single‑touch sensor using the MSP430 microcontroller.
The guide describes the operation principle of an open‑capacitance sensor, where a finger perturbs the electric field of a PCB‑mounted capacitor. It details the RC charge‑discharge method for measuring capacitance, the required high‑value resistor (~6 MΩ) and the low‑leakage I/O ports (≤50 nA) that enable ultra‑low‑power operation.
It also covers techniques for improving noise immunity, such as pseudo‑differential measurement and software low‑pass filtering, and provides guidance on building an experimental board (MSP430F2013 on the EXP430FG4618 platform). System resource usage is listed (1950 bytes ROM, 96 bytes RAM), along with PCB layout and cover‑layer considerations for reliable touch detection. This manual is written in Chinese.
| Recommended resistor value for sensor | ≈6 MΩ |
|---|---|
| Charging current with 6 MΩ resistor | ≈500 nA |
| Maximum I/O port leakage current | 50 nA |
| ROM usage of example application | 1950 bytes |
| RAM usage of example application | 96 bytes |
A high‑value resistor of about 6 MΩ is recommended, which limits the charging current to roughly 500 nA.
The example uses 1950 bytes of ROM and 96 bytes of RAM.
The MSP430 I/O ports have a maximum leakage current of 50 nA, making them suitable for low‑power capacitive sensing.