Many people set up greenhouses to grow tropical plants that need plenty of warmth and moisture. Usually these areas are enclosed in steel bracings holding glass/plastic panels that allow sunlight in and prevent moisture from going out. Greenhouse owners control the temperature by opening panels to allow ventilation. In winter, maintaining temperature could be difficult without use of heaters. Manually controlling temperature and humidity could be a tedious task taking away from the actual task of attending to the plants.
Therefore, an environment management system is an excellent way of controlling the weather within the greenhouse. Asa Wilson and his wife used a Raspberry Pi (RBPi) as the main computer for the environment management system for their greenhouse. They set up their greenhouse in Colorado on the western slope of Pike’s Peak. This place is notorious for its strong winds, while the normal growing season is very short.
As their greenhouse is rather small, measuring 10 x 12 ft., Asa uses a single temperature and relative humidity sensor. For larger greenhouses, the temperature and humidity at different locations will need to be monitored for effective control. Based on the input from the sensors, the RBPi controls the exhaust fans placed at opposite corners at the base of the greenhouse. The speed of these exhaust fans can be varied through custom speed control boards. Vents on the roof allow air to be drawn in when the exhaust fans are rotating. For air circulation, Asa uses a large oscillating fan mounted near the roof. The speed of this fan is set manually, and the RBPi can turn it on and off.
The greenhouse roof has four vents. Earlier, each vent could be opened with a single arm. However, that allowed the vents to vibrate in the wind, and they would sometimes close up. Asa designed and used vent controllers with geared motors and housed them in 3-D printed cases. The new vent controllers have two arms to hold each vent panel firmly on both sides, and this prevents any oscillations.
Initially, Asa used the RS232 protocol to let the RBPi talk to all the custom controllers. However, noise generated by the different devices caused communication issues. This led Asa to change over to RS485 drivers, which uses differential mode of communication for driving the signals. This solved the noise issue.
Although this is only a beginning, Asa is pleased with the results of his greenhouse. He is now planning for additional work. He is planning to add twenty more temperature sensors in the growing area for sensing temperature of individual plants, and a thermal controller for monitoring the sensors. He also plans to add seven water valves that will allow fine control on the humidity within the greenhouse.
Other people have also built automated greenhouses. For instance, David Dorhout has an automated watering robot that potters around carrying a 30-gallon tank for watering plants that need watering. Instrument Tek also has a similar greenhouse to Asa’s with an Arduino based system. In addition to watering and fan control, this also controls heat and communicates remotely to a computer.
