This application note describes how to implement a driven shield on STM8T and STM8TS capacitive sensors. Driven shields can be used to reduce the influence of metal objects, ground planes or nearby traces, thereby increasing the detection range of capacitive sensors.
The document addresses interference issues affecting the proximity detection range of STM8T and STMS8TS capacitive sensors, particularly when used near metal enclosures or ground planes. It details how metal objects and stray capacitances can reduce sensitivity and detection distance.
To mitigate these effects, the note describes the use of a driven shield feature available on selected devices. It explains the connection requirements for the SHLDIN and SHLDOUT pins, recommending the use of coaxial cables and specific resistor values to ensure the shield operates at the same potential as the sense antenna, thereby enhancing performance and reducing environmental interference.
The sensors can detect a user's proximity up to 30 cm.
A resistor with a typical value of 2 kΩ should be connected to the CX pin.
The pull-up resistor should be between 100 kΩ and 1 MΩ.