MSU Plant Growth Center
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The first part of the system is to collect the most heat possible from the solar heat collector. This is done with an analog temperature sensor comparator circuit. A temperature sensor will be placed inside of the reservoir and another one inside of the collector. The temperature sensors will be inputted into the control system and compared to each other. If the temperature inside the collector is greater than the temperature inside of the reservoir, there is a temperature gradient that allows the reservoir temperature to be increased. The two temperature sensors will be compared using a comparator circuit When the comparator circuit gives an on signal, Pump #1 will be turned on. This will pump the reservoir water through the solar heat collector to increase the temperature inside the reservoir. When T3 is less then T4, the pump will be turned off. In this situation, heat from the collector would be lost as it goes through collector.
The second part of the control system is to keep the garden bed temperature in the desired range. To do this, warm water will be pumped through the garden bed when the soil temperature decreases. Monitoring the soil temperature will be done with two temperature sensors on opposite sides of the garden bed. These temperature sensors will be inputted into the control system and compared to a fixed temperature range. These two soil temperatures will be compared independently allowing the system to utilize a 1 out of 2 voting scheme for soil temperature. The fixed comparator circuit that T1 and T2 will be compared to is shown in Figure 4. When the comparator circuit gives an on signal, Pump #2 will turn on, which will pump warm water through the garden bed, bringing the soil temperature up.When the soil temperature rises above 75 degrees, the circuit will shut the pump off to prevent the soil temperature from becoming too hot.The plot of the state of the pump vs. the soil temperature to view the theory behind how the soil temperature will fluctuate is shown below
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