IEEE 802.15.4 Based Wireless Sensor Networks Applied to pH and Temperature Monitoring in a Fish Farm

In the last years the number of papers related to wireless sensor networks has increased substantially. Most of the papers published treat the wireless sensor networks from a generic point of view, raising issues as routing algorithms, network life-time, and more recently, multiple input multiple output wireless networks. In contrast, we present in this paper a practical application for this kind of networks: The sensing of the pH and temperature for a fish farm. To develop this project, two different kind of modules have been included: The sensor and the wireless module. The sensor module collects the information and transmits it to the wireless module using a wired connection. Once the information is at the wireless node, it is transmitted to the central unit through a wireless protocol. The tasks of the central unit is the creation of the wireless network and the management of the received information. The sensor module includes an pH sensor based on a specifically designed ISFET and a commercial temperature sensor. Data collected from the sensor module is sent to the wireless node by an asynchronous wired serial polling communication. The use of this kind of protocol allows to connect a single master with multiple slaves nodes. For our particular case, we have connected one master with four slaves using a transmission rate of 9600 b/s. The wireless transmission follows the standard IEEE 802.15.4, and implements the routing protocol based on the zigbee standard. We have limited the number of nodes distributed on the fish farm up to 30 and the number of hops up to 6. Moreover, between the MAC and routing layer an energy management layer have been included. This layer allows to reduce the power consumption of the wireless network with an RF activity duty cycle for the reception stage at the final end device of about 0.02%.