3.8.1 The IoT Design Pattern: The 5-Step Blueprint

Programming a reliable IoT node follows a strict logical sequence:

1. Network Handshake: Connecting to Wi-Fi/GPRS (e.g., using WiFi.begin()).
2. Data Acquisition: Sampling sensors at the correct frequency (Nyquist rate).
3. Serialization: Converting C++ structs into JSON or Protobuf strings.
4. Transport: Publishing to an MQTT broker (topic-based) or sending an HTTP POST.
5. Control Loop: Subscribing to a "CMD" topic to receive real-time instructions (e.g., "Turn on Water Pump").

3.8.2 MQTT Implementation Snippet (Robust Pattern)

// Robust IoT Loop logic
void loop() {
  if (!client.connected()) reconnect(); // Never give up on the link
  client.loop(); // Process incoming packets
  
  long now = millis();
  if (now - lastMsg > 5000) {
    lastMsg = now;
    float t = dht.readTemperature();
    String payload = "{"temp":" + String(t) + "}";
    client.publish("home/livingroom/temp", payload.c_str());
  }
}

3.8.3 Robust Connectivity: The Reconnect Strategy

IoT devices must assume the network is "Lossy". Code must include a non-blocking reconnect logic to detect Wi-Fi/Broker drops and re-authenticate without stopping local safety logic.

3.8.4 Power-Aware Programming (Deep Sleep API)

For battery nodes that must last 5+ years:

// The "Sample -> Send -> Sleep" pattern
readSensor();
sendToCloud();
ESP.deepSleep(3600e6); // Sleep for 1 hour (units in microseconds)

In Deep Sleep, power consumption drops from 80mA (Active) to 10μA.

3.8.5 Unit 3 Review Questions (University Standard)

1. Describe the Hidden Terminal problem and its RTS/CTS solution.
2. Compare Contention-based (CSMA) and Schedule-based (TDMA) MAC protocols for IoT.
3. What is "Low Power Listening" (LPL) and how does it catch a sender's preamble?
4. Explain the concept of "Rank" in the RPL routing protocol.
5. Why is LEACH considered an energy-efficient routing protocol?
6. Define the difference between "Mesh-under" and "Route-over" routing in 6LoWPAN.
7. How does the "Whiteboard Approach" optimize Neighbor Discovery in IPv6 IoT?
8. Explain the 5-step sequence required to program a standard IoT node on Arduino.
9. Calculate the power savings achieved by using Deep Sleep (10uA) vs Idle (20mA).
10. What is the role of a callback function in MQTT programming?