This paper describes the concept and design of Orphion, a new digital musical instrument based on the Apple iPad. We begin by outlining primary challenges associated with DMI design, focussing on the specific problems Orphion seeks to address such as requirements for haptic feedback from the device. Orphion achieves this by incorporating an interaction model based on tonally tuned virtual “pads” in user-configurable layouts, where the pitch and timbre associated with each pad depends on the initial point of touch, touch point size and size variation, and position after the initial touch. These parameters control a physical model for sound generation with visual feedback provided via the iPad display. We present findings from the research and development process including design revisions made in response to user testing. Finally, conclusions are made about the effectiveness of the instrument based on large-scale user feedback.