This Arduino sketch demonstrates how to control a relay using a soil moisture sensor and two potentiometers to set the minimum and maximum thresholds for when the relay should turn on or off. The sketch also includes an i2c 1602 LCD display that shows the current sensor value, as well as the minimum and maximum threshold values.

• Arduino Nano
• Soil Moisture Sensor
• Relay Module
• 2 Potentiometers
• i2c 1602 LCD Display
• Jumper Wires

1. Connect the soil moisture sensor to the breadboard. Connect the positive (VCC) and negative (GND) leads of the sensor to the corresponding positive and negative rails on the breadboard. Connect the output (S) lead to a digital input pin (e.g. pin 2) on the Arduino Nano.
2. Connect the two potentiometers to the breadboard. Connect the center lead of each potentiometer to an analog input pin (e.g. A0 and A1) on the Arduino Nano. Connect the other two leads of each potentiometer to the positive and negative rails on the breadboard.
3. Connect the relay module to the breadboard. Connect the positive (VCC) and negative (GND) leads of the module to the corresponding positive and negative rails on the breadboard. Connect the input (IN) lead to a digital output pin (e.g. pin 3) on the Arduino Nano.
4. Connect the I2C LCD display to the breadboard. Connect the positive (VCC) and negative (GND) leads of the display to the corresponding positive and negative rails on the breadboard. Connect the SDA (data) and SCL (clock) leads of the display to the corresponding SDA and SCL pins (e.g. A4 and A5) on the Arduino Nano.
5. Connect the positive and negative rails of the breadboard to the corresponding positive (5V) and negative (GND) pins on the Arduino Nano. In this circuit, the potentiometers act as adjustable resistors that determine the minimum and maximum thresholds for the soil moisture sensor. The soil moisture sensor provides a value that is proportional to the moisture content of the soil. This value is read by the Arduino Nano and compared to the minimum and maximum thresholds set by the potentiometers. If the soil moisture value is below the minimum threshold, the relay is turned on. If the soil moisture value is above the maximum threshold, the relay is turned off. The I2C LCD display is used to display the current soil moisture value, as well as the minimum and maximum thresholds.

The sketch uses the following libraries:

• Wire.h for I2C communication with the LCD display
• LiquidCrystal_I2C.h for the LCD display

The sketch defines the following variables:

#define sensorPin A0   // Pin for the soil moisture sensor
#define relayPin 13     // Pin for the relay
#define minPotPin A1   // Pin for the minimum threshold potentiometer
#define maxPotPin A2   // Pin for the maximum threshold potentiometer

LiquidCrystal_I2C lcd(0x27, 16, 2);   // I2C address and dimensions for the LCD display

sensorPin is the pin number for the soil moisture sensor relayPin is the pin number for the relay minPotPin is the pin number for the minimum threshold potentiometer maxPotPin is the pin number for the maximum threshold potentiometer lcd is the instance of the LiquidCrystal_I2C class that is used to communicate with the LCD display

The setup function initializes the relay pin as an output and the LCD display:

void setup() {
  pinMode(relayPin, OUTPUT);   // Set the relay pin as an output
  lcd.begin();                  // Initialize the LCD display
}

The loop function reads the values of the soil moisture sensor and the two potentiometers, maps the values from 0 to 100, and sets the relay accordingly:

void loop() {
  int sensorValue = map(analogRead(sensorPin), 0, 1023, 0, 100);  // Read the sensor value and map it to 0-100
  int minThreshold = map(analogRead(minPotPin), 0, 1023, 0, 100);  // Read the minimum threshold and map it to 0-100
  int maxThreshold = map(analogRead(maxPotPin), 0, 1023, 0, 100);  // Read the maximum threshold and map it to 0-100

  // If the sensor value is below the minimum threshold, turn the relay on
  if (sensorValue < minThreshold) {
    digitalWrite(relayPin, HIGH);
  }
  // If the sensor value is greater than or equal to the maximum threshold, turn the relay off
  else if (sensorValue >= maxThreshold) {
    digitalWrite(relayPin, LOW);
  }

  lcd.clear();  // Clear the display
  lcd.setCursor(0, 0);  // Set the cursor to the first row, first column
  lcd.print("Value: ");
  lcd.print(sensorValue);
  lcd.print("%");
  lcd.setCursor(0, 1); // Set the cursor to the second row, first column
  lcd.print("Min: ");
  lcd.print(minThreshold);
  lcd.print("% Max: ");
  lcd.print(maxThreshold);
  lcd.print("%");

  delay(500); // Wait for 500 milliseconds
}

• sensorValue is the current value of the soil moisture sensor, mapped from 0 to 100.
• minThreshold is the minimum threshold value set by the minimum threshold potentiometer, mapped from 0 to 100.
• maxThreshold is the maximum threshold value set by the maximum threshold potentiometer, mapped from 0 to 100.

The if statement checks if the sensorValue is less than the minThreshold. If it is, the relay is turned on by setting the relayPin to HIGH. If the sensorValue is greater than or equal to the maxThreshold, the relay is turned off by setting the relayPin to LOW.

The LCD display is then updated to show the current sensorValue, as well as the minThreshold and maxThreshold. The display is cleared and the cursor is set to the first row, first column. The current sensorValue is printed, followed by the % symbol. The cursor is then set to the second row, first column. The text Min: is printed, followed by the minThreshold value and the % symbol. The text Max: is printed, followed by the maxThreshold value and the % symbol. The sketch then waits for 500 milliseconds before repeating the loop.

graph LR
A[Start] --> B(Setup)
B --> C[Initialize Pins and LCD]
C --> D[Loop]
D --> E{Read Sensor Value}
E -- Yes --> F{Sensor Value < Min Threshold?}
F -- Yes --> G[Turn Relay On]
F -- No --> H{Sensor Value >= Max Threshold?}
H -- Yes --> I[Turn Relay Off]
H -- No --> J[Update LCD Display]
J --> D
I --> J
E -- No --> J