Digital Output: LEDs and Relays

💡 Digital Output: Controlling LEDs and Relays with ESP8266

💡 What You'll Learn:

🔌 Control LEDs and relays with ESP8266
💧 Automate water pumps based on soil moisture
⚡ Understand active LOW vs active HIGH relays

🔧 Basic LED Control

#define LED_PIN 4  // D2 on NodeMCU

void setup() {
    pinMode(LED_PIN, OUTPUT);
    Serial.begin(115200);
}

void loop() {
    digitalWrite(LED_PIN, HIGH);  // LED ON
    Serial.println("🔴 LED ON");
    delay(1000);
    
    digitalWrite(LED_PIN, LOW);   // LED OFF
    Serial.println("⚫ LED OFF");
    delay(1000);
}

💧 Relay Control for Water Pump

#define RELAY_PIN 5  // D1 on NodeMCU

void setup() {
    pinMode(RELAY_PIN, OUTPUT);
    digitalWrite(RELAY_PIN, HIGH);  // Start with pump OFF
    Serial.begin(115200);
}

void waterPump(int seconds) {
    digitalWrite(RELAY_PIN, LOW);   // Turn pump ON (active LOW)
    Serial.printf("💧 Water pump ON for %d seconds\n", seconds);
    delay(seconds * 1000);
    digitalWrite(RELAY_PIN, HIGH);  // Turn pump OFF
    Serial.println("💧 Water pump OFF");
}

void loop() {
    // Replace with actual soil moisture sensor reading
    int soilMoisture = 25;  // 0-100%
    
    if (soilMoisture < 30) {
        Serial.println("⚠️ Soil dry - Starting irrigation");
        waterPump(10);  // Water for 10 seconds
    } else {
        Serial.println("✅ Soil moisture adequate");
    }
    
    delay(60000);  // Check every minute
}

💡 Important Notes:

Most relay modules are active LOW → LOW = ON, HIGH = OFF
Always test your relay to confirm which state turns it on
Use a resistor (220Ω) with LEDs to prevent damage
Never connect pump directly to ESP8266 - always use a relay

⚠️ Common Issues:

Relay clicks but pump doesn't run: Check COM and NO connections (not NC)

ESP8266 resets when relay activates: Use external 5V power for relay

LED doesn't light: Check polarity (long leg to positive)

🎉 Quick Reference:

pinMode(pin, OUTPUT) → Set pin as output

digitalWrite(pin, HIGH) → Set pin HIGH (3.3V)

digitalWrite(pin, LOW) → Set pin LOW (0V)

delay(ms) → Wait for milliseconds

💡 Key Takeaways:

Apply these concepts directly to your farm or project.

Take notes on important details for the quiz.

Use the button below to track your progress.

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