If you need a straightforward solution for a control knob on your project, the Dial Phidget is just what you need. It uses an optical encoder, so it has fully continuous rotation with none of the dead zones or physical wear that potentiometer-based dials have. The HIN1101 connects to a port on a VINT Hub. See the Comaptible Products tab for a list of hubs.
When the dial is pressed down, a DigitalInput object will change from false to true, so your program can use the change event to trigger a function or feature of your project.