Site-Specific Water and Chemical Application by Wireless Valve Controller Network

Abstract

Variations in plant water and nutrient demand and environmental regulations to protect water quality provide significant justification for development of site-specific irrigation and fertigation systems. We have developed wireless valve controllers that self-assemble into a mesh network. Mesh networking means that controllers pass messages to extend the effective communication range without using high power radios. Solar energy is collected with a 200 mW panel to operate each controller node without yearly battery replacement. Nine nodes were tested in a mesh network and each properly responded to commands. Measurements of battery voltage, solar panel voltage, enclosure temperature, and external sensors were transmitted every 10 minutes. Irrigation schedules were stored locally on each node and executed automatically. Schedules for each node were unique, based on the needs of the particular area being irrigated. Internal clock drift was an average 6.3 s per day. Clock offset was removed using daily time stamps. One-hop transmission range using 916 MHz radios varied from 20.9 m with a whip antenna at ground level to 241.1 m with a dipole antenna mounted at 3 m. Node commands were acknowledged after an average of 2.7 s per hop. Daily charge consumption was approximately 6.76 mA·h for the node and 1 mA·h per day for battery self-discharge. The solar panel produced 26.0 to 81.3 mA·h in direct sunlight and 6.5 to 13.7 mA·h in shade. Node operation is expected to be continuous with occasional sunlight exposure. Soil moisture, pressure, temperature, and other environmental sensors will be used for feedback control and detection of problems. Such a network of intelligent valve controllers will allow growers in orchards, vineyards, nurseries, greenhouses, and landscapes to develop management practices that improve water and fertilizer use efficiency.