Smart Plant Monitor with OLED Display + Auto Watering Using Wemos D1 Mini

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

// OLED display size
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

// Pin definitions
#define SOIL_SENSOR_PIN 16  // D0 on Wemos D1 Mini (A0 is GPIO17, but you use GPIO16 here)
#define ENA_PIN 15          // PWM pin for motor speed control (GPIO15)
#define IN1_PIN 13          // Motor direction control pin 1 (GPIO13)
#define IN2_PIN 12          // Motor direction control pin 2 (GPIO12)

#define MOISTURE_THRESHOLD 1000  // Threshold for dry soil

bool motorActivated = false; // State to prevent repeated watering cycles

void drawFace(int x, int y, int mood) {
  // Draw circular face
  display.drawCircle(x, y, 20, SSD1306_WHITE);      // Face outline
  display.fillCircle(x - 6, y - 6, 4, SSD1306_WHITE); // Left eye
  display.fillCircle(x + 6, y - 6, 4, SSD1306_WHITE); // Right eye

  if (mood == 1) { // Happy face (Wet)
    display.drawLine(x - 7, y + 8, x - 3, y + 10, SSD1306_WHITE);
    display.drawLine(x - 3, y + 10, x + 3, y + 10, SSD1306_WHITE);
    display.drawLine(x + 3, y + 10, x + 7, y + 8, SSD1306_WHITE);
  } else { // Sad face (Dry)
    display.drawLine(x - 7, y + 10, x - 3, y + 8, SSD1306_WHITE);
    display.drawLine(x - 3, y + 8, x + 3, y + 8, SSD1306_WHITE);
    display.drawLine(x + 3, y + 8, x + 7, y + 10, SSD1306_WHITE);
  }
}

void setup() {
  Serial.begin(115200);

  // Initialize OLED
  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println(F("SSD1306 allocation failed"));
    for (;;); // Halt
  }

  display.clearDisplay();
  display.display();

  // Initialize pins
  pinMode(SOIL_SENSOR_PIN, INPUT);

  pinMode(ENA_PIN, OUTPUT);
  pinMode(IN1_PIN, OUTPUT);
  pinMode(IN2_PIN, OUTPUT);

  // Ensure motor is off at start
  digitalWrite(IN1_PIN, LOW);
  digitalWrite(IN2_PIN, LOW);
  analogWrite(ENA_PIN, 0);
}

void loop() {
  // Read soil moisture sensor
  int soilValue = analogRead(SOIL_SENSOR_PIN);
  Serial.print("Soil sensor value: ");
  Serial.println(soilValue);

  // --- OLED Display Update ---
  display.clearDisplay();

  if (soilValue > MOISTURE_THRESHOLD) {
    // Dry soil detected
    drawFace(100, 32, 0); // Sad face on right side

    display.setTextSize(2);
    display.setTextColor(SSD1306_WHITE);
    display.setCursor(10, 10);
    display.println("Dry");

    display.setCursor(10, 30);
    display.println("Soil");
  } else {
    // Wet soil detected
    drawFace(100, 32, 1); // Happy face on right side

    display.setTextSize(2);
    display.setTextColor(SSD1306_WHITE);
    display.setCursor(10, 10);
    display.println("Wet");

    display.setCursor(10, 30);
    display.println("Soil");
  }

  display.display();

  // --- Motor Control Logic ---
  if (soilValue > MOISTURE_THRESHOLD) {
    if (!motorActivated) {
      Serial.println("Motor ON - Watering for 5 seconds");
      digitalWrite(IN1_PIN, HIGH);
      digitalWrite(IN2_PIN, LOW);
      analogWrite(ENA_PIN, 125); // Approx 49% speed

      delay(5000); // Water for 5 seconds

      // Turn motor off
      digitalWrite(IN1_PIN, LOW);
      digitalWrite(IN2_PIN, LOW);
      analogWrite(ENA_PIN, 0);

      motorActivated = true;
      Serial.println("Motor OFF after watering");
    } else {
      Serial.println("Soil still dry, motor already activated. No action.");
    }
  } else {
    if (motorActivated) {
      Serial.println("Soil moist detected. Resetting motor activation flag.");
      motorActivated = false;
    } else {
      Serial.println("Soil moist, motor remains off.");
    }
    // Ensure motor is off
    digitalWrite(IN1_PIN, LOW);
    digitalWrite(IN2_PIN, LOW);
    analogWrite(ENA_PIN, 0);
  }

  delay(2000); // Delay before next reading
}

Software Setup (version 2)

include <ledcontrol.h></ledcontrol.h>
// Pin definitions for your LED matrix wiring
#define DIN_PIN 15   // D8 (GPIO15)
#define CS_PIN 13    // D7 (GPIO13)
#define CLK_PIN 12   // D6 (GPIO12)

// Capacitive soil sensor analog input pin
#define SOIL_SENSOR_PIN 16  // D0 (GPIO16)

LedControl lc = LedControl(DIN_PIN, CLK_PIN, CS_PIN, 1); 

// Smiley face pattern
byte smiley[8] = {
  0b00111100,
  0b01000010,
  0b10100101,
  0b10000001,
  0b10100101,
  0b10011001,
  0b01000010,
  0b00111100
};

// Sad face pattern
byte sad[8] = {
  0b00111100,
  0b01000010,
  0b10100101,
  0b10000001,
  0b10011001,
  0b10100101,
  0b01000010,
  0b00111100
};

// Pin definitions
const int relay1Pin = 0;  // D3 (GPIO0) to relay input 1
const int relay2Pin = 2;  // D4 (GPIO2) to relay input 2

// Threshold for dry soil detection (adjust based on your sensor calibration)
const int dryThreshold = 1000;  // example threshold for analog reading (0-1023)

// State variable to prevent repeated activation
bool motorActivated = false;

void setup() {
  Serial.begin(115200);
  
  pinMode(relay1Pin, OUTPUT);
  pinMode(relay2Pin, OUTPUT);
  pinMode(SOIL_SENSOR_PIN, INPUT);
  
  lc.shutdown(0, false);    // Wake up MAX7219
  lc.setIntensity(0, 8);    // Set brightness (0-15)
  lc.clearDisplay(0);       // Clear display
  
  // Initialize relays off (assuming LOW activates relay, so HIGH means off)
  digitalWrite(relay1Pin, HIGH);
  digitalWrite(relay2Pin, HIGH);
  
  delay(2000); // Wait for sensor stabilization
}

void displayFace(byte face[8]) {
  for (int row = 0; row < 8; row++) {
    lc.setRow(0, row, face[row]);
  }
}

void loop() {
  int soilValue = analogRead(SOIL_SENSOR_PIN);  // Read soil moisture sensor
  
  Serial.print("Soil sensor analog value: ");
  Serial.println(soilValue);
  
  // Display sad face if soil is dry (value >= threshold), else smiley face
  if (soilValue >= dryThreshold) {
    displayFace(sad);
  } else {
    displayFace(smiley);
  }
  
  // Relay control logic
  if (soilValue >= dryThreshold) {
    // Soil is dry
    if (!motorActivated) {
      Serial.println("Soil dry detected. Activating motor for 5 seconds.");
      digitalWrite(relay1Pin, LOW);  // Activate relay 1 (motor ON)
      digitalWrite(relay2Pin, LOW);  // Activate relay 2 if needed
      delay(5000);                   // Keep motor ON for 5 seconds
      digitalWrite(relay1Pin, HIGH); // Deactivate relay 1 (motor OFF)
      digitalWrite(relay2Pin, HIGH); // Deactivate relay 2
      motorActivated = true;         // Prevent repeated activation
      Serial.println("Motor deactivated after 5 seconds.");
    } else {
      Serial.println("Soil still dry, motor already activated. No action.");
    }
  } else {
    // Soil is wet
    if (motorActivated) {
      Serial.println("Soil moist detected. Resetting motor activation flag.");
      motorActivated = false;        // Reset flag to allow future activation
    } else {
      Serial.println("Soil moist, motor remains off.");
    }
    digitalWrite(relay1Pin, HIGH);   // Ensure relay is off
    digitalWrite(relay2Pin, HIGH);
  }
  
  delay(2000);  // Wait before next reading
}

Code Breakdown

Version 1

Libraries Used:

• Wire.h – Enables I2C communication (used by OLED).
• Adafruit_GFX.h – Core graphics library for displays.
• Adafruit_SSD1306.h – Specific library for controlling OLED (SSD1306)
  
  

OLED Display Setup:

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1

• Initializes a 128x64 OLED display with no reset pin.

Moisture Threshold:

#define MOISTURE_THRESHOLD 1000

• When the analog soil reading exceeds 1000, the soil is considered dry.

drawFace() Function:

• Draws a simple smiley or sad face depending on soil moisture.
• Used to add a fun, emotional touch to plant health feedback.

setup() Function:

• Initializes serial communication, OLED display, and motor pins.
• Ensures the motor is off at startup.
  
  

loop() Function:

• Reads soil sensor value.
• Displays either "Dry Soil 😢" or "Wet Soil 😊" on the OLED.
• If dry and motor hasn't yet run:
• Activates motor (5 seconds) using L298N and PWM.
• If wet, resets motor state and ensures it's off.
  
  

 Version 2

Library Used:

• LedControl.h – Used to control MAX7219-based 8x8 LED matrix modules.
  
  

Pin Definitions:

#define DIN_PIN 15
#define CS_PIN 13
#define CLK_PIN 12
#define SOIL_SENSOR_PIN 16
const int relay1Pin = 0;
const int relay2Pin = 2;

• DIN, CS, CLK – Communication pins to control the LED matrix.
• relay1Pin/relay2Pin – Connected to relays that activate the water pump.

Smiley & Sad Face Arrays:

byte smiley[8] = { ... };
byte sad[8] = { ... };

• These binary arrays define how the emoji faces are drawn on the 8x8 matrix.
  
  

setup() Function:

Initializes:

• Serial communication
• Relay pins (off by default)
• Soil sensor
• LED matrix (brightness and clearing display)

loop() Function:

• Reads soil moisture sensor value.
• Displays a smiley or sad face on the matrix.
• If soil is dry and motor not yet triggered:
• Activates relay for 5 seconds to water the plant.
• Then turns motor off and sets a flag.
• If soil becomes moist again, the motor flag resets for future activation.

Video Demonstration

 Version 1: Smart Plant Monitor with OLED + Auto Watering

Version 2: Smart Plant Monitor with 8x8 Matrix LED + Auto Watering

Conclusion

The Smart Plant Monitor with Auto Watering System showcases a practical and creative approach to automating plant care through real-time soil monitoring and automatic watering. This project not only helps maintain healthy plants but also introduces users to essential IoT and automation concepts.

Two versions of the system were developed to suit different preferences and component availability. Version 1 uses an OLED Display and L298N Motor Driver, offering a clean, compact, and beginner-friendly interface with the added benefit of precise motor control via PWM. It provides clear, readable feedback and a more advanced level of customization which is perfect for users who value detail and control.

On the other hand, Version 2 uses an 8x8 Matrix LED and Relay Module, adding a fun and charming twist by displaying expressive pixel-style emojis to indicate plant mood. It offers a more engaging and visually appealing experience, especially suited for hobbyists, students, and quick builds where simplicity is key.

Both versions provide an accessible, practical solution for maintaining healthy plants—especially useful for users who may forget or be too busy to water their plants on time. The system promotes smart gardening and introduces users to IoT and automation principles through hands-on experience.

References

• YouTube – "Soil Moisture Sensor with Wemos D1 Mini and Relay"
• YouTube – "MAX7219 8x8 LED Matrix with Arduino – Smiley Face Display Tutorial"
• CreateLabz Internal Resources and Component Datasheets
• Adafruit OLED and GFX Libraries
• LedControl Library Documentation
• ESP8266/ESP-12 Module Documentation
• Arduino IDE Official Documentation