Design of wireless sensor network system based on in-field soil water content monitoring

For finding a way to retrieve, transmit and store data in large-scale, full-coverage soil water content monitoring, a wireless sensor network system was developed and tested. The system was composed of ten sensor nodes, one central node to collect data from the sensor nodes and one base node connected to a PC to retrieve, store, and present the data. Soil water contents at four depths, i.e., 5.00, 15.24, 30.48 and 60.96cm below soil surface, were continuously monitored. TinyOS and ZigBee were applied as operation system and communication protocol, respectively. EC-5 low-power and low-cost soil moisture sensor was applied. Solar powering module met the energy requirements of both sensor and central nodes. Packet delivery rate (PDR) experiment results indicated that, overall, a stable data transmission was achieved since 7 out of 10 sensor nodes’ PDR were higher than 90% and another one was 89.2%. Due to manufacturing imperfection, two sensor nodes’ PDR was lower than 70%. This problem was fixed by replacing powering circuits of the two nodes.