An experimental setup to monitor and control the humidity and temperature of a container is developed. The different hardware components will be elaborately discussed in what follows.
In order to quantify the environmental conditions as well as possible, a combined humidity/temperature sensor is used to gather this information. Two different sensors are tested for this project, the DHT11 and DHT22 sensor. Both sensors are similar but the DHT22 provides a better accuracy and a larger measuring range. The humidity is sensed with a polymer that changes conductivity with the humidity and the temperature is obtained via a basic thermistor. This basic design makes these sensors both accurate and low cost. The measurements are transmitted to a Raspberry Pi microprocessor via an one-wire communication protocol.
The humidity is controlled with an ultrasound air humidifier which disperses an ultra-fine mist of water droplets in the air to increase the humidity. This mist is directed via PVC piping to the actual container that holds the dewpal collectors. This piping gives time for the droplets to evaporate and adds to the humidity in the chamber.
The humidifier is constructed for manual control and in order for the controller to actuate this humidifier, a relay module is used to disconnect the humidifier from the power supply when the desired humidity is reached. This electrically operated switch receives a low voltage signal from a Raspberry Pi microprocessor and closes the higher voltage circuit powering the humidifier.
At the heart of our do-it-yourself humidistat lies the Raspberry Pi microprocessor. This microprocessor performs a handful of tasks. On the software side it executes a closed-loop control algorithm to control the humidity of the humidistat and writes the temperature, humidity and humidifier actions to CSV files for further analysis. On the hardware side, it communicates with the sensor and actuates the relay module.