L1

Lesson 1 : Getting started

What is IOT ?

connecting the Internet to the physical world via sensors (hardware)(The ‘T’ part of IOT, they are the things)

Architecture of an little IOT system

*-----------------------------------------------------------------------*              *----------*
| Controller (MCU or Raspberry Pi)( Be able to execute instructions )   |   <--------> | Internet |
*---------------------*------------------------*------------------------*              *----------*
                      |        GPIO  pins      |  
                      *------------------------*
                           ||             ||
                        Sensors        Actuators

1. Sensors collect data from physical world and send them to Controller through GPIO pins
2. Controller process the data(Simple conditional logical/Machine Learning Model decisions/send they to cloud to process) and give a feed back(Feed back data/Do nothing) to Actuators
3. Actuators using the feed back data to operate and influence the physical world(red lights turn to green/rotate to certain degree/make some noise/water the plant)

What’s the difference between IOT and embedded systems ?

Embedded system is a subset of IOT.

IOT	Embedded system
More computation resource	Simple and restricted resource
Access to network and cloud service	Working alone
IOTs talks to each other (cooperation)	No connection between each other

IOT on the edges

IOT can also work without the Internet.

The Cloud/Internet can be replaced by a local data processing center such as PC or server serves as a gateway, the gateway download AI models from the Internet and then use it locally.

Air wall/gap

Since IOT is a easy prey for hackers, separate your private network with the IOTs due to their Internet connection.

Type of sensors

Property	Analog sensors	Digital sensors
Output	continuous analog signal	discrete digital signal
Result	the scale of votage	is there a signal ? a number is read
Signal type	sin wave	square wave
Example	temperature sensor	button
Converter	ADC (Analog-Digital-Converter)	ADC is also necessary for digital sensors

(DAC is used in the Analog Actuators, converting digital control signals to analog signals to activate the actuator)

Pulse width modulation

Control the speed of a motor via a trick in code.

This involves sending lots of short digital pulses that act as if it was an analog signal.

What’s a relay ?

Relay is commonly used as a digital signal switch, you send digital signal in, then a magnatic switch on/off.

The magnatic switch control the on/off of the main power supply.

How data transmit between Cloud and Devices ? (What’s the paradigm ?)

using a broker

• Just like YouTube/Bilibill the telemetry and commands are organized by a subscribe and publish/notify scheme.
• The device and cloud can be the publisher and subscriber at the same time.(Just like users)
• MQTT test website mosquitto
• Each MQTT user should have an unique ID.
• Topics can have subtopics, just like file hierarchy.