💡 Digital Output: Controlling LEDs and Relays with ESP32

Digital output allows you to control external devices like LEDs, buzzers, and relays. This is how you'll control water pumps, lights, and alarms in your IoT projects. A relay can switch pumps on/off automatically - no manual intervention needed!

🔧 How Digital Output Works

• HIGH (1): Pin outputs 3.3V (enough to power a small LED)
• LOW (0): Pin outputs 0V (GND - completes the circuit)
• Use pinMode(pin, OUTPUT) to set pin as output
• Use digitalWrite(pin, HIGH/LOW) to set the value
• ⚠️ Never connect pumps directly to ESP32! Always use a relay module.

📊 Pin Reference for Digital Output

💡 Basic LED Control Example

/*
 * LED Control - Farm Status Indicator
 * Connect LED anode (long leg) → 220Ω resistor → GPIO4
 * Connect LED cathode (short leg) → GND
 */

#define LED_PIN 4

void setup() {
    pinMode(LED_PIN, OUTPUT);
    Serial.begin(115200);
    Serial.println("🌱 Farm Status LED Ready");
}

void loop() {
    // Blink pattern: ON for 1 second, OFF for 1 second
    digitalWrite(LED_PIN, HIGH);
    Serial.println("🔴 LED ON - System active");
    delay(1000);
    
    digitalWrite(LED_PIN, LOW);
    Serial.println("⚫ LED OFF");
    delay(1000);
}
    

💧 Water Pump Relay Control (Active LOW)

/*
 * Automatic Water Pump Control with Relay
 * Connect relay IN pin → GPIO5
 * Connect relay VCC → 3.3V, GND → GND
 * Water pump connects to relay COM and NO terminals
 * 
 * ⚠️ Most 5V relays are ACTIVE LOW:
 * - digitalWrite(LOW) = Pump ON
 * - digitalWrite(HIGH) = Pump OFF
 */

#define RELAY_PIN 5
#define SOIL_MOISTURE_THRESHOLD 30

void setup() {
    pinMode(RELAY_PIN, OUTPUT);
    digitalWrite(RELAY_PIN, HIGH);  // Start with pump OFF
    Serial.begin(115200);
    Serial.println("💧 Smart Irrigation System Started");
}

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

void loop() {
    // Read soil moisture (replace with actual sensor reading)
    int soilMoisture = analogRead(32);
    int moisturePercent = map(soilMoisture, 3800, 1500, 0, 100);
    moisturePercent = constrain(moisturePercent, 0, 100);
    
    Serial.printf("💧 Soil moisture: %d%%\n", moisturePercent);
    
    if (moisturePercent < SOIL_MOISTURE_THRESHOLD) {
        Serial.println("⚠️ Soil too dry! Starting irrigation...");
        waterPump(10);  // Water for 10 seconds
    } else {
        Serial.println("✅ Soil moisture adequate - No watering needed");
    }
    
    delay(60000);  // Check every minute
}