Re Remote Data Acquisition and IoT 01219335 Data Acquisition and - - PowerPoint PPT Presentation

Re Remote Data Acquisition and IoT

Chaipo Chaiporn J n Jaik aikae aeo De Department of f Computer Engineering Ka Kasetsart Unive versity

01219335 Data Acquisition and Integration

Revised 2020-09-02 Materials partly taken from lecture slides by Karl and Willig

2

Ou Outline

• Remote data acquisition
• Communication pattern in IoT
• MQTT protocol
• Programming examples

3

sensor field

Re Remote Data Acquisition

• Sensor nodes communicate to a gateway via radio links

radio links

Remote monitoring Network

gateway

4

Da Data-Ce Centri ric Networki rking

• Typical networking interaction is node-centric
• Client/server, peer-to-peer
• Desirable properties for IoT applications
• Decoupling in space – neither sender nor receiver may need to

know their partner

• Decoupling in time – ”answer” not necessarily directly triggered by

“question”, asynchronous communication

5

Da Data-Ce Centri ric Networki rking Mo Model

Internet

D a t a Interest Interest D a t a

6

Pu Publish/Subscribe Interaction

• Idea
• Entities can publish data under certain names
• Entities can subscribe to updates of such named data
• Variations
• Topic-based
• Content-based

Software bus Publisher 1 Publisher 2 Subscriber 1 Subscriber 2 Subscriber 3

7

MQ MQTT T Protocol

• Message Queue Telemetry Transport
• Light-weight messaging protocol designed for connecting

edge IoT devices

• Uses publish/subscribe pattern to interconnect devices
• Operates on top of TCP, but works well with intermittently

connected links

8

MQ MQTT T Operation

MQTT Broker

T

• p

i c :

• f

f i c e / r

• m

2 / t e m p P a y l

• a

d : 2 6

p u b l i s h

Topic: office/room2/temp

s u b s c r i b e

Topic: office/room2/temp Payload:26

s u b s c r i b e

T

• p

i c :

• f

f i c e / + / t e m p Topic: office/room2/temp Payload: 26

MQTT clients

9

Ad Advantages of MQTT

• Decouples publishers and subscribers
• Allows message reception without long polling
• Uses very short message headers
• Supports multiple quality of services
• Allows NAT traversal

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MQ MQTT T vs.

• s. HTTP

TP

• HTTP
• MQTT

request response broker Icon made by Smashicons from www.flaticon.com

subscribe publish publish subscribe publish subscribe p u b l i s h

11

MQ MQTT T Cl Client Tools

• PC (Windows/macOS/Linux)
• Chrome app: MQTTLens
• Command-line tool: Mosquitto
• Android
• MyMQTT
• IoT MQTT Panel
• iOS
• MQTTool

12

MQ MQTT T Cl Client Librari ries

• Eclipse Paho Project
• Various implementations for many platforms and languages
• MicroPython’s umqtt module
• Light-weight MQTT client implementation
• Two variations
• umqtt.simple
• umqtt.robust
• Already built into standard MicroPython firmware

13

Pu Public MQTT Brokers

• HiveMQ
• broker.hivemq.com
• Mosquitto
• test.mosquitto.org
• Many more can be found on
• https://github.com/mqtt/mqtt.github.io/wiki/public_brokers

14

MQ MQTT T Topic Naming

• A topic name consists of one or more topic levels

(UTF-8 strings), separated by a forward slashes

• E.g.,
• Topics are case-sensitive
• ku/cpe is not the same as Ku/Cpe

ku/cpe/room204/temperature

topic level topic level topic level topic level

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Su Subscrip iption ion W Wild ildcar ards

• Wildcards may be used for subscription
• Single-level wildcard (+)
• Replaces only one topic
• Multi-level wildcard (#)
• Replaces many topic levels
• MUST be placed at the end of a topic
• Some best practices are described here:
• https://www.hivemq.com/blog/mqtt-essentials-part-5-mqtt-

topics-best-practices

ku/cpe/+/temperature ku/cpe/#

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MQ MQTT: Stack

MQTT SSL (optional) TCP IP Application

default port: 1883 default port: 8883

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MQ MQTT T Co Connection and Keep Alive

MQTT Client MQTT Broker

CONNECT CONNACK SUBSCRIBE SUBACK PUBLISH PUBLISH PINGREQ PINGRESP

⋮ ⋮ ⋮ ⋮

Connection establishment Regular activities Keep alive

DISCONNECT

⋮

Disconnection

18

Qualit Quality o

• f S

f Ser ervic ice (Qo e (QoS) Le ) Levels els

• QoS 0 - at most once
• Fire and forget
• QoS 1 - at least once
• Msg gets resent until PUBACK

is received

• QoS 2 - exactly once
• Achieved through four-way

handshake

https://www.hivemq.com/blog/mqtt-essentials-part-6-mqtt-quality-of-service-levels/

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Las Last W Will & ill & T Testame ament (L (LWT)

• IoT devices may get disconnected ungracefully
• Unstable wireless connection
• Battery depletion
• A client can publish a LWT in advance
• In case of unexpected disconnection of the client, all

subscribed clients will get a message from the broker

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Re Retained Messages

• A newly subscribed client may have missed previously

published data

• A message published with the retain flag set will be

delivered to a newly subscribed client

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Sc Scenar ario 1 io 1 – Pu Publishing Data

Internet

MQTT Broker

periodically publish light status

subscribe for light status

Light sensor

22

De Devi vice Op Operation

• n
• Connect KidBright to the local WiFi (e.g., KUWIN)
• Connect to a local MQTT broker
• Measure and publish light value every 2 seconds to the

topic ku/cpe/room204/light

23

Co Code: I/O Setup

• Create an ADC object associated with Pin 36

from machine import Pin, ADC ldr = ADC(Pin(36))

24

Co Code: Wi WiFi Co Connection

• Create WLAN connection with

WLAN class in the network module

• Replace SSID and PASS with

appropriate values

• wlan.connect() method is not

blocking, so the code keeps checking wlan.isconnected() to ensure connectivity before further proceeding

• Use on-board red LED (IO2) for

WiFi connection indicator

import time import network from machine import Pin led_wifi = Pin(2, Pin.OUT) led_wifi.value(1) # turn it off wlan = network.WLAN(network.STA_IF) wlan.active(True) print("*** Connecting to WiFi...") wlan.connect("SSID","PASS") while not wlan.isconnected(): time.sleep(0.5) print("*** Wifi connected") led_wifi.value(0)

25

Co Code: MQ MQTT T Br Broker r Co Connection

• Replace UNIQUE-ID and BROKER with appropriate values
• mqtt.connect() blocks until a connection is successfully

established

• Use on-bard green LED (IO12) to indicate broker connection

from umqtt.robust import MQTTClient led_iot = Pin(12, Pin.OUT) led_iot.value(1) # turn it off mqtt = MQTTClient("UNIQUE-ID","BROKER") print("*** Connecting to MQTT broker...") mqtt.connect() print("*** MQTT broker connected") led_iot.value(0)

26

Co Code: Publish shing Light Values

• mqtt.publish() method requires strings or byte arrays for both

topic and payload arguments

while True: value = ldr.read() print("Publish light:", value) mqtt.publish("ku/cpe/room204/light", str(value)) time.sleep(2)

27

Sc Scenar ario 2 io 2 – Su Subscrib ibin ing

Internet

MQTT Broker

• subscribe for lamp control
• set lamp status

publish LED value

Connect USB lamp here

28

De Devi vice Op Operation

• n
• Connect KidBright to the local WiFi (e.g., KUWIN)
• Connect to a local MQTT broker
• Connect USB lamp to KidBright's USB port
• Subscribe to ku/cpe/room204/lamp and use the

published value to change the lamp status

• Payload is 0 → turn the lamp off
• Payload is 1 → turn the lamp on
• Other payloads should be properly ignored

29

Co Code: I/O O Se Setup

• USB-switch output is connected

to IO25

• Logic 1 à Power off
• Logic 0 à Power on

from machine import Pin lamp = Pin(25, Pin.OUT) lamp.value(1) # turn it off

30

Co Code: Wi WiFi Se Setup

• Connect to WiFi with

appropriate SSID and PASS

• Again, use the on-board red

LED for WiFi connection indicator

import time import network from machine import Pin led_wifi = Pin(2, Pin.OUT) led_wifi.value(1) # turn it off wlan = network.WLAN(network.STA_IF) wlan.active(True) print("*** Connecting to WiFi...") wlan.connect("SSID","PASS") while not wlan.isconnected(): time.sleep(0.5) print("*** Wifi connected") led_wifi.value(0)

31

Co Code: MQ MQTT T and Subsc scri ription

• Replace UNIQUE-ID and BROKER

with appropriate values

• Call mqtt.set_callback()

method to set the callback function before making any subscription

• Call mqtt.check_msg()

regularly to check for incoming messages

• sub_callback() is called

automatically with byte arrays in topic and payload arguments

from umqtt.robust import MQTTClient led_iot = Pin(12, Pin.OUT) led_iot.value(1) # turn it off def sub_callback(topic,payload): if topic == b"ku/cpe/room204/lamp": try: lamp.value(1-int(payload)) except ValueError: pass mqtt = MQTTClient("UNIQUE-ID","BROKER") print("*** Connecting to MQTT broker...") mqtt.connect() print("*** MQTT broker connected") led_iot.value(0) mqtt.set_callback(sub_callback) mqtt.subscribe(b"ku/cpe/room204/lamp") while True: mqtt.check_msg()

32

Ex Exer ercise 4. ise 4.1: 1: D Dimmable Io immable IoT Lamp Lamp

• Modify the last example so that user can control the

brightness of the USB-powered lamp by publishing a value between 0-100 to ku/daq2020/<nickname>/lamp

• Payload is 0 → Lamp is completely off
• Payload is 100 → Lamp is completely on
• Payload is any value between 0 to 100 → Lamp’s brightness is

adjusted accordingly (the greater, the brighter)

• Other payloads should be properly ignored without crashing the

program

33

Furt Further R her Rea eadi ding ngs

• HiveMQ’s MQTT Essentials
• https://www.hivemq.com/mqtt-essentials/
• MQTT standard v3.1.1
• http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-
• s.pdf
• MQTT standard v5.0
• https://docs.oasis-open.org/mqtt/mqtt/v5.0/mqtt-v5.0.pdf
• umqtt’s source code and API reference
• https://github.com/micropython/micropython-

lib/tree/master/umqtt.simple

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Co Conclusi sion

• IoT devices are typically resource-constrained and
• perating under unreliable Internet connections
• Data-centric communication where devices are decoupled

in both time and space is desirable for IoT

• MQTT is a light-weight and disconnection-tolerant protocol

that allows devices to interact with pub/sub pattern