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+<code C main.cpp>
+#include <Arduino.h>
+#include <WiFi.h>
+#include <MQTT.h>              // 256dpi MQTT library
+#include <ArduinoJson.h>
+#include <Adafruit_NeoPixel.h>
+//////////////// EDIT THESE ////////////////
+const char* WIFI_SSID     = "YOUR_SSID";
+const char* WIFI_PASSWORD = "YOUR_PASSWORD";
+const char* MQTT_HOST     = "test.mosquitto.org";   // or your lab broker
+const uint16_t MQTT_PORT  = 1883;
+const char* BASE_TOPIC    = "iot/studentname";        // change per student
+////////////////////////////////////////////
+#define NEOPIXEL_PIN 3
+Adafruit_NeoPixel pixel(1, NEOPIXEL_PIN, NEO_GRB + NEO_KHZ800);
+WiFiClient net;
+MQTTClient mqtt(1024);         // 1KB message buffer
+// ---------- Wi-Fi ----------
+void ensureWiFi() {
+  if (WiFi.status() == WL_CONNECTED) return;
+  WiFi.mode(WIFI_STA);
+  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
+  Serial.print("WiFi connecting");
+  while (WiFi.status() != WL_CONNECTED) {
+    delay(400);
+    Serial.print(".");
+  }
+  Serial.printf("\nIP: %s\n", WiFi.localIP().toString().c_str());
+}
+// ---------- MQTT message handler (256dpi signature) ----------
+void onMessage(String &topic, String &payload) {
+  Serial.printf("MQTT msg on %s: %s\n", topic.c_str(), payload.c_str());
+  // Create a dynamic document on the stack with a defined capacity
+  JsonDocument doc;
+  DeserializationError err = deserializeJson(doc, payload);
+  if (err) {
+    Serial.printf("JSON parse error: %s\n", err.c_str());
+    return;
+  }
+  int r = doc["r"] | 0;
+  int g = doc["g"] | 0;
+  int b = doc["b"] | 0;
+  int brightness = doc["brightness"] | 50;
+  pixel.setPixelColor(0, pixel.Color(r, g, b));
+  pixel.setBrightness(brightness);
+  pixel.show();
+  // Acknowledge
+  String ackTopic = String(BASE_TOPIC) + "/led/ack";
+  JsonDocument ack;  // also replace StaticJsonDocument here
+  ack["ok"] = true;
+  ack["r"] = r;
+  ack["g"] = g;
+  ack["b"] = b;
+  ack["brightness"] = brightness;
+  char buf[96];
+  size_t n = serializeJson(ack, buf, sizeof(buf));
+  mqtt.publish(ackTopic, String(buf, n));
+}
+// ---------- MQTT connect / subscribe ----------
+void ensureMQTT() {
+  if (mqtt.connected()) return;
+  String clientId = "sparrow-c6-led-" + String((uint32_t)ESP.getEfuseMac(), HEX);
+  Serial.println("MQTT connecting...");
+  while (!mqtt.connect(clientId.c_str())) {
+    Serial.print(".");
+    delay(1000);
+  }
+  Serial.println("\nMQTT connected");
+  String sub = String(BASE_TOPIC) + "/led";
+  mqtt.subscribe(sub);
+  Serial.printf("Subscribed: %s\n", sub.c_str());
+}
+void setup() {
+  Serial.begin(115200);
+  delay(200);
+  pixel.begin();
+  pixel.clear();
+  pixel.show();
+  // Broker + transport setup and callback
+  mqtt.begin(MQTT_HOST, MQTT_PORT, net);
+  mqtt.onMessage(onMessage);
+}
+void loop() {
+  ensureWiFi();
+  ensureMQTT();
+  // Process incoming packets and keepalive
+  mqtt.loop();
+  delay(10);
+}
+</code>