This application note introduces the AD7142 capacitive-to-digital converter IC and the PCB sensors used to construct a capacitance sensing solution.
This document explains the factors influencing capacitance sensing technology, specifically focusing on the AD7142 capacitive-to-digital converter IC. It analyzes how the size and type of the sensor element, the size of the object touching the sensor, and the properties of the covering material impact sensor performance.
The text provides specific recommendations for designing button and slider sensors, including optimal sizes and plastic thickness limits. It includes data on dissipation factors for various plastic polymers and guidelines for ensuring reliable sensor activation and position data output.
| Excitation Signal Frequency | 240kHz |
|---|---|
| Capacitive Field Extension | about 4 mm |
| Button Sensor Minimum Size | 5 mm x 5 mm |
| Recommended Plastic Thickness | maximum of 2mm |
Materials such as plastic or glass are suitable covering materials, but metal cannot be used.
The covering plastic should have a maximum thickness of 2mm to ensure proper sensor operation.
A smaller object, such as a small finger or probe, can only decrease the measured capacitance by a small amount, resulting in a smaller sensor response.