1 Introduction

OpenSCAD is a free software application for creating solid 3D CAD objects. It is a script-only based modeler that uses its own description language; parts can be previewed but cannot be interactively selected or modified by the mouse in the 3D view. OpenSCAD is free and released under the General Public License version 2. OpenSCAD is available from http://www.openscad.org/. It is also available for macOS® and Linux® operating systems.

The version at the time of this writing is 2019-05. Although the primary strength of OpenSCAD is 3D rendering, its 2D capabilities are perfect for creating 2D capacitive electrode shapes that can be quickly manipulated by simple modifications to the script parameters that control the various attributes of the design.

The sensor design scripts are provided by Texas Instruments under a BSD license so you are free to modify them if needed. These scripts create and manipulate primitive objects that are assembled into complex slider and wheel sensor designs, using only these seven OpenSCAD commands:

square()

circle()

translate()

rotate()

hull()

difference()

intersection()

For information about these commands, refer to the OpenSCAD user guide.

This document does not cover the theory of capacitive touch or provide design guidelines for construction and layout of capacitive sensors on a PCB, but it does illustrate common slider, wheel and, touchpad sensor designs and their geometric features that relate to the corresponding script parameters.

It is assumed the reader has some familiarity with capacitive touch technology, slider or wheel sensors and sensor design principles. If new to capacitive touch, visit http://www.ti.com/captivate for information about MSP430™ capacitive touch sensing microcontrollers and http://www.ti.com/captivatetechguide for sensor design guidelines.

NOTE

The PCB examples provided in this document are demonstrated using Altium Designer 19. Refer to your PCB CAD tool documentation to perform the equivalent steps.