Smart Trigger for Ultralow Power and Time Critical WSN Applications

Wireless Sensor Networks (WSN) contain sensor nodes powered by limited batteries. How to solve the tension between real-time reactivity to external events and energy saving for long lifetime is one major challenge. Duty cycle scheduling provides a method to balance the tension based on the application scenarios. However, time critical WSN applications often put strict requirements on both ends, quick response and long lifespan. In this paper, we propose a hardware invention called Smart Trigger to detect external events with ultra low power before activating the sensor node for precise measurements. By using passive transducers, the smart trigger consumes only a few microwatts and reacts to surrounding changes within one millisecond. Our solution consists of three generic modules which can be integrated into any kind of sensor nodes. We tested four types of passive transducers to monitor four typical environmental conditions. Our experimental results show high accuracy of detection and ultra low power consumption. Furthermore, we build a generic model to evaluate monitoring efficiency of duty cycle scheduling in comparison with environment triggering policy. We also describe a few WSN applications which can be automated by environment triggered sensor nodes. This paper presents an implementation of smart trigger and demonstrates significant energy saving in the model.