Abstract

A methodology for designing Wireless Camera Network nodes featuring long lifetime is presented. Wireless Camera Networks may nd widespread application in the elds of security, animal monitoring, elder care and many others. Unfortunately, their development is currently thwarted by the lack of nodes capable of operating autonomously for a long period of time when powered with a couple of AA batteries. In the proposed approach, the logic elements of a Wireless Camera Network node are clearly identied along with their requirements in terms of processing capabilities and power consumption. For each element, strategies leading to significant energy savings are proposed. In this context, the employment of a custom vision sensor and an ecient architecture are crucial. In order to validate the methodology, a prototype node is presented, mounting a smart sensor and a ash-based FPGA. The node implements a custom algorithm for counting people, a non trivial task requiring a considerable amount of on-board processing. The overall power consumption is limited to less than 5 mW, thus achieving a two orders of magnitude improvement with respect to the state of the art. By powering the system with two batteries providing 2200 mAh at 3.3 V, the expected lifetime of the system exceeds two months even in the worst-case scenario.