LightLink: Enhancing Smartwatch Sensing and Actuation Through Visible Light Communication

Smartwatches are equipped with fixed sensors (e.g., ECG, IMUs) or actuators designed for a broad audience. However, some users need specialized smartwatch functionality, creating a demand for add-on devices that extend a smartwatch's capabilities. Our work explores the design of add-on devices that communicate with the smartwatch using visible light. To demonstrate the feasibility of our approach, we conduct a series of characterization experiments to assess the ability of the smartwatch's ambient light sensor and screen as a light-based receiver and transmitter, respectively, and develop strategies for establishing a reliable communication link. Our approach is low-cost, has minimal instrumentation of a smartwatch, and supports the addition of input and output capabilities. To validate our approach, we design and test a suite of add-ons that expand the sensing (e.g. buttons, body temperature, etc.) and output (visual feedback and haptic wristband) capabilities of the smartwatch. We also contribute a toolkit framework comprising our hardware designs and a software library that enables designers and developers to quickly create applications that integrate add-ons with smartwatches using our approach.