Design and construction

Operating diagram

As control elements for the modulation of temperature and relative humidity, a lamp and extractors located on the ridge and at the back of the greenhouse are used. To increase the humidity of the soil, spray irrigation is used and to decrease it, the extractor at the back of the greenhouse.

Circuit diagram

The electronic circuit is mainly composed of the Arduino UNO platform which receives the data temperature from the digital sensor DHT11, soil moisture from the hygrometer sensor FC - 28, pH from the pH sensor v1.1. Arduino processes and controls these parameters through an integrated circuit ULN2003 that acts as an external power switch for the actuators composed of some relays that when activated feed the fans, irrigation system, heating, cooling and purifier. Arduino sends the temperature, humidity and pH variables in a serial way to the Bluetooth HC-06 module and transmits them via Bluetooth to a cell phone with Android operating system. Thanks to a proprietary application, designed on the App Inventor platform, it is possible to view the parameters received from all sensors in real time and keep informed about the current status of the greenhouse.

Flowchart

The program starts by asking if the numerical value of the temperature is between 20°C and 28°C. If the condition is met, the digital outputs for the temperature actuators are kept "LOW", in case the condition is not met it asks again if the temperature is lower than 20ºC, so the digital output for the actuators will be set to "HIGH" and will turn on the heater, on the other hand if the temperature value is higher than 28ºC, the digital output for the Peltier cell cooling system actuator will be set to "HIGH". It then asks if the numerical value of the soil moisture is between 40% and 60%. If the condition is true, the actuators are kept in a "LOW" state, if the condition is false, it asks again if the humidity value is less than 40%, if the condition is true, the actuator for the irrigation system and the actuator for the purifier are set to "HIGH", but if the condition is false it asks again if the humidity is greater than 60%, in this case the actuator for the extractors will be set to "HIGH". Finally the condition given is if the pH level is 7.0, if the condition is true the output for the purifier is activated and if the condition is false the actuators for the pH is kept at a low level.

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