IoT Based Greenhouse Monitoring System using Raspberry Pi

A Raspberry Pi greenhouse monitor. Sensors measure temperature, light, humidity and soil moisture, and the readings are uploaded online so the grower can check and control the greenhouse remotely.

12 V power adapter / step-down transformer supplies the circuit; a regulator gives the controller and sensors a steady 5 V. The Soil moisture sensor measures how wet the soil is so watering happens only when needed. The PIR motion sensor detects human movement from the change in infrared heat. The Temperature sensor measures the temperature that the system monitors or controls.

The Raspberry Pi is a full computer with an operating system, so it can run Python, OpenCV and a web server. An Arduino is a microcontroller that is better for simple real-time control but cannot process images or run multiple programs.

The two probes measure the soil's resistance. Wet soil conducts better, so the resistance and output voltage change, which tells the controller when to start the pump.

It has two pyroelectric elements that see infrared from different zones. When a warm body moves across them, the difference changes and the sensor gives a HIGH output.

LM35 gives an analog output of 10 mV per °C, so 250 mV means 25 °C. The controller reads it with the ADC and converts the value to degrees.

An LDR is made of cadmium sulphide. In light its resistance drops to a few hundred ohms, and in darkness it rises to about a megaohm. Used in a voltage divider, it gives a voltage that depends on light.

The input section senses the real-world quantity, the Raspberry Pi 4 processes it according to the program, and the output section acts locally and sends the data or alert wirelessly. The power supply section feeds every block.

UART (serial) for the GSM, GPS, Bluetooth or fingerprint modules, I2C for the display, RTC or motion sensor (only SDA and SCL lines), a single-wire digital protocol for the temperature sensor and analog inputs read by the ADC for the analog sensors. Each protocol was chosen because the module supports it and it uses the fewest pins.

The controller and most sensors work at 5 V (ESP boards and some modules at 3.3 V). A 12 V adapter powers the board, and a regulator steps it down. Motors and relays get their own supply line so they do not reset the controller.

Accuracy is how close a reading is to the true value. Precision is how close repeated readings are to each other. A sensor can be precise but inaccurate if it is not calibrated.