Products with capacitive touch sensor interfaces are more common than ever and typically feature a few button sensors or maybe a collection of buttons, such as a keypad. The button sensors provide a simple "touch" or "no touch" user input and their typical round or square shape can be created easily with a PCB CAD design tool. As product interfaces evolve, interfaces are beginning to include more complex sensor types, such as a slider, wheel, or touchpad. Designing these types of capacitive touch sensors shapes with a PCB CAD design tool can require a considerable amount of time, even for the best engineers and PCB designers. And even after the design has been completed, changes in product requirements often force the designer to make modifications to the design or completely start the design over. Automating the design steps can all but eliminate this time consuming process.

This application report describes how to create scalable self-capacitive slider, wheel, and touchpad sensors with OpenSCAD, a free Solid 3D CAD modeling tool, and custom scripts created by Texas Instruments. Modifying the script parameters and running the script generates a new sensor pattern that can be exported to DXF format then easily imported into any PCB CAD tool. This flexibility and speed makes it now possible to create complex sensor shapes effortlessly.

The scripts described in this document can be downloaded from http://www.ti.com/lit/zip/slaa891.