Design and test of wireless drip irrigation control in orchard with low-power

Abstract: In China, commercial electricity was not available in most mountain orchards. Therefore, low-power systems are required. On the other hand, strong demands for developing automatic irrigation systems also existed in those areas. It's also important to implement the central management strategy for those irrigation systems. Wireless networks could be helpful in transmitting soil moisture information and monitoring irrigation status. Taking advantage of wireless networks in the irrigation system for further implementation of a central control strategy is becoming a hot topic in irrigation engineering. This paper is aimed at providing a low-cost and low-power wireless irrigation solution for small-scale orchard growers to realize automatic time-control irrigation. The system was composed of several nodes, each node of hardware consisted of a MSP430F2132 micro controller, a short range RF transceiver (CC1100, Texas Instrument), an RS-232 interface for long distance communication module, an LCD (liquid crystal display, JLX12865-0086PC) module, a 9 V Battery module, a valve driving circuit and a soil moisture sensor (Decagon EC-5 or other) interface. Time synchronization communication protocol was designed for system nodes; therefore, the whole system could enter the sleep mode when there was no irrigation task. Furthermore, the WOR (wake on radio) feature of the RF module also helped to reduce power consumption of the nodes when the nodes were woken up for synchronization. The system power consumption test was performed under 9 V battery voltage; the quiescent current consumption is 400 μA. While the WOR current consumption was 19 mA, the current consumption of the system was 439 μA on average. Calculations also indicated that the charge of daily operating a pulse solenoid valve covers only a tiny portion in a whole node's daily charge. The battery discharge experiment in the conditioning of 100 mA const current revealed that the selected battery module could provide a charge of 400 mAh. In the test, output voltage dropped from 9 V to 5 V. According to the estimation, the system could run for at least 38 days without changing batteries. Communication tests in mountain orchards showed that the minimum packet loss rate when nodes were randomly distributed was 6.19%, the effective communication distance with 3 dBi antenna on each node reached 70m. The RSSI (received signal strength index) did not show a significant difference in the experimental orchard compared with open field RSSI experiment results, but the packet loss rate was much higher when in the deep orchard. The test of long distance communication module showed that the PLC (power line communication) Module (Zinwell PWQ-5101) had few chances to establish a successful data link while the GPRS and high power WiFi module held a stable data link between the remote monitoring terminal and the control system. The system was utilized for irrigation control, irrigation valves were turned on every day at 8:00 am, the collected soil moisture showed a rapid increase when valves were turned on and decreased slowly after irrigation valves were turned off, the time control error was less than 5 minutes and soil moisture rate was maintained above 13% during experiment periods. These tests proved that this system could be suitable for mountain orchards in southern China.