Solar Powered Passive Wireless Moisture Sensor with Cloud Communication

Abstract

Studies have shown that fresh water is getting scarcer worldwide day by day. Most of the fresh water is being wasted on land fields for irrigation. Farmers waste so much fresh water, when watering their crops. To conserve water, measurements need to be done efficiently. However, soil moisture sensors currently available on the market are quite expensive and have high power consumption to be used in developing countries extensively. Currently, ICT technologies moving at a rapid pace has resulted in a broad domain called, Internet of Things (IoT), which is becoming more and more ubiquitous. They are being deployed as part of smart solutions for purposes as remote monitoring and automation, to solve individual as well as social needs. In this work we present a new solar powered passive moisture sensor, which is a low cost alternative moisture sensor with low power consumption. To reduce the power consumption we took two approaches. Firstly, we target to reduce the power consumption during operation and secondly, we aim to harvest solar energy to prevent battery depletion. The Passive moisture sensor measures the volumetric water content in soil by means of two electrodes composed of different metals, such as copper and zinc. The potential difference between the metals changes with the change of moisture in the soil. Since, the measurements are based on the potential difference between the metals there is no energy consumed by the node. We show that measurements performed by the passive moisture sensor correlates with the measurements performed by the commercial moisture sensor, such as, Decagon EC5. Our passive moisture sensor solution is at least 30% less expensive than other solutions currently available on the market. To reduce the energy consumption as much as possible, we let both main components of the sensor node, microcontroller and radio, duty cycle independently of each other. Therefore, we have developed the Harmonic-Medium Access Control (H-MAC) protocol which ensures that the duty cycle of both components do not conflict with each other. And allows the communication between the sensor nodes and Cloud to be bi-directional. H-MAC makes the network scalable and resilient to failure. With H-MAC the radio has lower duty cycle, lower energy consumption and has lower latency than X-MAC. Further, to ensure that the batteries of the nodes last for as long as possible we powered the nodes with solar energy. Since, solar energy is not consistent we need to predict when will the sun provide enough energy to power the sensor nodes. We show that by using the weather forecasting and insert information about solar radiation and sunshine duration into our prediction model we get an improvement of about 10% on the prediction of solar energy availability. In this work we provide convincing results that our passive moisture sensor is a low cost, low power alternative