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The sensor positions and the cooler fans and heater positions needs to be identified by testing for the appropriate positions. It also depends on the size of the greenhouse as the size of the greenhouse increase the temperature will not be constant and therefore more than one sensor needs to be used. The same applies to soil water level sensor. In the prototype made it is still possible to add two more sensors to the system along with two more fans and a solenoid valve and still display the temperature and soil moisture level detected from the added sensors in the LCD display. But by this means the greenhouse would have two temperature and soil water level control systems and these two systems can be used to monitor and control the temperature and soil water level in two sectors of a large greenhouse.
Using one LDR sensor for the whole greenhouse is much suitable since light is falling equally into the greenhouse and the sensor needs to be placed in a place where it is directly subjected to light from the sun and as well as from the light bulbs.
The system also can be implemented to an existing greenhouse without any problem. Only the ideal position of the heater and the fans needs to be identified by a trial and error method. Laying pipes is also easy as they are placed close to the plant and the sensor may be kept at some distance away from the water pipes to ensure that the soil further away from the plant will also be moistened since the roots of the plants are spread and it is the tip of the rot that absorb more water and this tip is found further away from the plant.
When implementing the system proper calibration of the LDR and the soil moisture sensor needs to be done. A flux meter can be used to calibrate the LDR where different voltages between the fixed resistor are measured for different intensities of light measured using the flux meter. By this means a lookup table can be made and the LDR can be calibrated accordingly. The soil moisture sensor can also be calibrated by looking at the respective datasheet for that model.
Currently the temperature, light intensity and soil moisture is regulated around a particular value. But when implementing practically it is more efficient to regulate these parameters around a range of values even though the values do no frequently change.