Reducing energy consumption by a low-current real-time clock on a ZigBee networking device

In order to extend the lifespan of wireless sensor networks, the trade-off between power saving and workload for battery-powered wireless sensors must be taken into account. Most wireless sensor devices use most of their battery charge for wireless communication or processing tasks. A proposed economical approach to prolonging network lifespan is to enable wireless sensors to switch to an energy-saving sleep mode whenever possible. A sleep timer is generally used to set the period during which a device enters and exits low-power sleep mode. However, a deep-sleep mode may even halt the clock completely until an external signal wakes up the system kernel. In this regard, this paper implements an ultra-low power wireless sensor device which is able to enter deep-sleep mode, and which only draws hundreds of nano-amperes for the majority of the device's operation. In a non-real-time and self-awakening scenario, it is possible to set the kernel in such a way as to enter sleep mode and wake up with a given periodicity, or when a critical event occurs.