Development of a wireless sensor network for algae cultivation using ISFET pH probes

We present a wireless sensor network to measure pH, dissolved oxygen (DO), and temperature for use in algae cultivation. The pH is measured using ion sensitive field effect transistor (ISFET) technology, which is more robust and has a faster response than traditional glass pH electrodes. A custom circuit drives the ISFET sensor and interfaces with an ANT wireless network system. The wireless network consists of a network hub which can service up to 8 sensor nodes and a series of relays to transmit the data to a PC. The data is logged with a custom LabVIEW program. In this work, we demonstrate operation of this network using 5 sensors (3 ISFET pH, 1 DO, 1 temp), one hub, and two relay units. The network was used to collect data for 42 days from a 1600 L raceway tank growing Scenedesmus dimorphus. In that time, the network did not experience any failures beyond what can be mitigated with additional battery capacity and improved construction methods. At the end of the growth cycle, the daily variation in dissolved oxygen was observed to closely track the optical density measurements.