Add minimal single relay example for testing and beginners

examples/single_relay_test/single_relay_test.ino

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+/*
+ * ESP32 Single Relay Test - Minimal Example
+ * 
+ * This is a simplified version for testing just ONE relay
+ * Perfect for beginners or initial hardware testing
+ * 
+ * Hardware Setup:
+ * - Connect ESP32 5V to Relay Module VCC
+ * - Connect ESP32 GND to Relay Module GND  
+ * - Connect ESP32 GPIO 13 to Relay Module IN1
+ * 
+ * Commands via Bluetooth:
+ * - ON: Turn relay on
+ * - OFF: Turn relay off
+ * - STATUS: Check relay state
+ */
+
+#include "BluetoothSerial.h"
+
+BluetoothSerial SerialBT;
+
+// Relay configuration
+const int RELAY_PIN = 13;  // Change this to your GPIO pin
+bool relayState = false;
+
+void setup() {
+  // Start serial for debugging
+  Serial.begin(115200);
+  Serial.println("ESP32 Single Relay Test");
+  
+  // Configure relay pin
+  pinMode(RELAY_PIN, OUTPUT);
+  digitalWrite(RELAY_PIN, HIGH);  // Start with relay OFF (active LOW)
+  
+  // Start Bluetooth
+  SerialBT.begin("ESP32-Test-Relay");
+  Serial.println("Bluetooth ready! Device: ESP32-Test-Relay");
+  Serial.println("Commands: ON, OFF, STATUS");
+}
+
+void loop() {
+  // Check for Bluetooth commands
+  if (SerialBT.available()) {
+    String command = SerialBT.readStringUntil('\n');
+    command.trim();
+    command.toUpperCase();
+    
+    Serial.println("Received: " + command);
+    
+    if (command == "ON") {
+      relayState = true;
+      digitalWrite(RELAY_PIN, LOW);  // Active LOW relay
+      SerialBT.println("Relay is ON");
+      Serial.println("Relay is ON");
+    }
+    else if (command == "OFF") {
+      relayState = false;
+      digitalWrite(RELAY_PIN, HIGH);  // Active LOW relay
+      SerialBT.println("Relay is OFF");
+      Serial.println("Relay is OFF");
+    }
+    else if (command == "STATUS") {
+      String status = relayState ? "ON" : "OFF";
+      SerialBT.println("Relay: " + status);
+      Serial.println("Relay: " + status);
+    }
+    else {
+      SerialBT.println("Unknown command. Use: ON, OFF, or STATUS");
+    }
+  }
+  
+  delay(10);
+}