This paper presents a detailed description of the development of a wireless audio-visual interface that is integrated with a violin bow. This interface is a work-in-progress prototype resulting from a practice-based research project into optimal physical design and software mappings for the virtuoso string player. As an augmented instrument, this interface aims at extending the existing skill set of the performer. Moving away from gestural analysis approaches, we focus more directly on optimising real-time performer interaction and control for violin performance, using bow hand fingers to manipulate the interface. A further novel aspect is the equal emphasis placed on both the audio and visual real-time processing which unlocks potential for new compositional possibilities and interdisciplinary performance situations. Frugal in its physical design, the interface is made up of two intentionally small sensors housed in a 3D printed casing which is designed to prevent requirements for alterations to the violin bow. The sensors are instrumented to communicate wirelessly with the software system, with mappings being developed within a common digital audio environment. Used within two different performance situations, this interface was evaluated from an expert performer’s perspective with discussion on future design iteration possibilities.