Comprehensive temperature controller with internet connectivity for plant growth experiments

The experimental control of temperature is key to many scientific and applied endeavors, particularly for studying the effects of greenhouse-gas driven warming on plant performance. Unfortunately, numerous nuisances in the control of temperature for plants renders most commercially available controllers unsuitable or too expensive. Here we describe a simple to use but comprehensive temperature controller for plant growth experiments in enclosed spaces like nurseries or chambers. The device uses Pulse Width Modulation to control independent cooling and heating elements over a broad range of amperages, which minimizes or eliminates temperature overshoot and ensures precise and accurate temperature control (i.e., sensor accuracy = 0.1 °C; controller accuracy = 0.3 °C.). The device incorporates an internal clock for controlling temperature (and growth lights) concurrent with diurnal cycles, and it has an integrated Wi-Fi chip to transfer sensor data to a web-page, where data are displayed in real time. The device uses off-the-shelf parts and can be built for around $USD63. The controller can be integrated with other reported controllers (e.g., soil moisture and CO2) to produce an affordable multi-system controller necessary for complex factorial experiments, which hopefully can help to accelerate our understanding about the impacts of climatic variables on plant performance.