An energy neutral wearable camera with EPD display

Wearable technologies are flooding the consumer market, and have massively entered the market of electronic consumers and people are now surrounded by an increasing number of "smart" objects to wear. The main issue that limits the success of these devices is limited battery lifetime. Energy-neutral operation, which does not require battery recharging or replacement (similar to automatic quartz watches) is highly desirable in this context. In this paper, we present the first energy-neutral wearable device, equipped with an ultra low power camera and an electrophoretic display (EPD) which is supplied by a solar energy harvester. The novel design includes several hardware and software optimizations to achieve energy neutrality. In particular, we implemented innovative methods for displaying gray-scale images to obtain up to 9 gray-scale levels using a black-and-white display. This reduces by 43.7% the energy consumption in comparison to the state of art. Moreover, we implemented aggressive power management for the camera acquisition which saves up to 91.4% of energy to acquire an image. Experimental results, with different scenarios, demonstrate advanced functionality and the energy neutrality of the system that can acquire and display up to 54 images per hour in indoor scenario.