What is IoT

• Not “a computer connected to the internet”
  • Then it is really just another computer connected to the internet
• Must be something else
  • It is simply devices that are resource constrained
    • Usually in more than one way
• Autonomous operation, the connection might not be permanent

IoT is just a concept

• The Internet of Things (IoT) is the network of physical devices, vehicles, home appliances and other items embedded with electronics, software, sensors, actuators, and connectivity which enables these objects to connect and exchange data.¹

What is an IoT Device?

What is an IoT Device?

• Constrained in (one or more of):
  • Memory
  • CPU
  • Network bandwidth and/or latency
  • Storage
• Has connectivity
  • Bluetooth
  • Wi-Fi
  • NB-IoT
  • LTE Cat-M
  • LoRA
  • Proprietary radio

IoT Devices - Bluetooth 4/5 chips

• nRF52810: High performance, entry-level Bluetooth 4/ANT/2.4GHz SoC
• nRF52832: High performance Bluetooth 4/ANT/2.4GHz SoC
• nRF52840: Advanced multi-protocol System-on-Chip Supporting: Bluetooth 5, ANT/ANT+, 802.15.4 and 2.4GHz proprietary

IoT Devices - LoRA

Modules

Chips

IoT Devices - NB-IoT

IoT Devices - Wi-Fi

ESP32 - dual cpu, Wi-Fi, Bluetooth 4 ESP32-D0WDQ6 2x Xtensa @ 160MHz $ 4.53 @ 10

ESP8266 details - Power usage

What is the internet again?

OSI model

1. Physical Layer
2. Data Link Layer
3. Network Layer
4. Transport Layer
5. Session Layer
6. Presentation Layer
7. Application Layer

• Wikipedia: OSI model
• Wikipedia: OSI model#Examples

Layer 1: Physical Layer

• 10BASE5, 10BASE2
• 10BASE-T / 100BASE-TX / 1000BASE-TX
• 802.11a/b/g/n PHY
• RS-232

Layer 2: Data Link Layer

• Ethernet
• WiFi
• Bluetooth
• Token Ring

Layer 3: Network Layer

• IP
• ICMP
• IPX

Layer 4: Transport Layer

• TCP
• UDP

Layer 5: Session Layer

• “sockets”
• NetBIOS

Layer 6: Presentation Layer

• SSL

Layer 7: Application Layer

• HTTP
• DNS
• MQTT
• CoAP
• (everything else..)

Details: IP

Details: UDP

TODO: add payload to “ip packets”

NodeMCU hardware

NodeMCU hardware

ESP8266 software layers

ESP8266 + Arduino

• Standard Arduino IDE
• ESP8266 Arduino core
  • https://github.com/esp8266/Arduino

Arduino IDE

Arduino code structure

void setup() {
    // Called once
}

void loop() {
    // Called repeatedly
}

Arduino file structure

foo/
  foo.ino
  config.h

Generic Arduino APIs

// Pin: D0, D1, etc.
// Mode: OUTPUT, INPUT, INPUT_PULLUP
void pinMode(uint8_t pin, uint8_t mode);

// State: HIGH, LOW, true/false, 1/0
void digitalWrite(uint8_t pin, uint8_t state);
int digitalRead(uint8_t pin);

unsigned long now millis();
unsigned long now micros();

ESP Arduino APIs

class {
    void restart();
    uint32_t getFreeHeap();
    uint32_t getChipId();

    ...
} ESP;

// Usage
ESP.restart();

ESP Arduino APIs

class {
    String macAddress();

    wl_status_t status();
    int32_t RSSI();

    IPAddress localIP();
    IPAddress subnetMask();
    IPAddress gatewayIP();
    IPAddress dnsIP(uint8_t dns_no = 0);

    ...
} WiFi;

// Usage:

Serial.println(WiFi.localIP().toString());

MQTT

• Message Queuing Telemetry Transport
• Wikipedia: MQTT

MQTT - Implementations

• Mosquitto
• Eclipse Paho
• RabbitMQ
• ActiveMQ

MQTT Cloud Connectors

• Cloud
  • Amazon IoT
  • Google Cloud IoT
  • Microsoft Azure IoT
  • CloudMQTT (at Heroku)
• DIY
  • ThingMQ
  • HiveMQ

MQTT - The protocol

Agents have one of two roles:

• Client
  • Publishes messages
  • Subscribes / unsubscribes to topics
• Broker (aka Server)
  • Handles network connections
  • Keeps subscriptions
  • Manages client
    • Disconnects
    • (last) will
  • Persistence of retained messages

MQTT - The protocol - MQTT Packet

• Size oriented
• Flags indicate type of remaining bytes
  • Packet type
  • Topic name
  • Payload

MQTT - The protocol - Keep alive

TODO

MQTT - The protocol - MQTT Topic

• Topic name: foo/bar/baz
• Topic filter
  • foo/bar/?
  • foo/#

MQTT - The protocol - Retained message

Message is kept by the server even after disconnect

• CONNECT
• PUBLISH
  • RETAIN
  • $app/$device/temperature
  • 22.3
• DISCONNECT

Later on:

• SUBSCRIBE
  • $app/#/temperature
• PUBLISH
  • $app/$device/temperature
  • 22.3

MQTT - The protocol - Will message

Message sent when you disconnect

Client #1:

1. CONNECT
   • WILL TOPIC: $app/$device/online
   • WILL PAYLOAD: 0
2. PUBLISH
   • $app/$device/online
   • 1
3. DISCONNECT

Broker

1. To all subscribers PUBLISH
   • $app/$device/online
   • 0

MQTT - The protocol - Client id

TODO

Device and application architecture with MQTT

MQTT Topic

The temperature sensor:

• Publishes on:
  • myapp/$device-id/temperature
  • myapp/$device-id/humidity
  • myapp/$device-id/altert
• Subscribes to:
  • myapp/$device-id/command

The central application:

• Subscribes to:
  • myapp/#/temperature
  • myapp/#/humidity
• Publishes on:
  • myapp/$device-id/command

MQTT on Arduino

PubSubClient is our MQTT client implementation.

WiFiClient wifiClient;
PubSubClient mqtt(wifiClient);

void callback(char* topic,
              byte* payload,
              unsigned int length);

void setup() {
    // Configure WiFi
    mqtt.setServer(mqtt_server, 1883);
    mqtt.setCallback(callback);
}

MQTT on Arduino

void loop() {
    if (!mqtt.connected())
        reconnect();
    else
        mqtt.loop();
    // Do work
}

void reconnect() {
    while (!mqtt.connect(client_id));

    mqtt.subscribe(topic_pattern);
}

Assignment

• mqtt

MQTT topic architecture

The central application is split:

• An aggregating agent:
  • myapp/#/temperature
  • myapp/#/humidity
• Emailing agent
  • myapp/$device-id/altert
• Publishes on:
  • myapp/$device-id/command

MQTT - Patterns

• Combining MQTT and HTTP
• Using web sockets transport

Assignment

• mqtt2

Assignment

• mqtt3