An energy neutral wearable camera with EPD display

Wearable technologies are ooding the consumer market, and have massively entered the market of electronic con-sumers 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 life-time. Energy-neutral operation, which does not require bat-tery 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 dis-play (EPD) which is supplied by a solar energy harvester. The novel design includes several hardware and software op-timizations 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 consump-tion in comparison to the state of art. Moreover, we imple-mented aggressive power management for the camera acqui-sition 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 sys-tem that can acquire and display up to 54 images per hour in indoor scenario.