[Mooc]IoT Course 3 Interfacing with the Arduino

Week 1

Reading a schematic
Using a breadboard
Resistors
Diodes
LEDs

Lesson 1

Lecture 1.1 Electrical Circuits

Hardware and Software

• IoT devices combine hardware and software
• Hardware interacts with the world
• Software is the "intelligence"

Electrical Circuits

• Electrical current flowing though wires
• Battery/power supply moves current

Lecture 1.2 Electrical Properties

Voltage

• Voltage(V) : Potential difference between two points in the circuit
• Like pressure in a water system
• Pressure difference is what counts
• Measured in volts

Current

• Current(I) : Rate of carrier flow
• Flows from positive to negative
• Electrons flow from negative to positive
• Measured in amperes

Resistance

• Resistance(R) : Any obstacle to current flow
• For water, might be a rock or narrow pipe
• For circuits, might be a bad conductor or narrow conductor

Lecture 1.3 Ohm's Law

Ohm's Law

V=I*R

• Expresses the relationship between V,I and R
• Used to compute one value given the other 2
• Some common uses:
  • What resistor do I need to limit current flow
  • What voltage can I expect for a given resistance

Lesson 2

Lecture 2.1 Electrical Components

Resistors

• Provides resistance to current flow
• Two terminals; no difference between them
• Band colors indecate resistor size
  • Each color is a digit; scientific notation is used

Battery/DC Power

• Provides voltage via power and ground
• Do not Create a short circuit

Lecture 2.2 Diodes

Diodes and LEDs

• Two terminals: Anode > Cathode
• Current only flows in one direction, anode to Cathode
  • One-way valve
• LEDs light when current flows

Diode Threshold Voltage

• Anode-Cathode voltage must be above threshold
  • Threshold depends on diode
• Reverse-biased: when anode is negative wrt cathode

Diode Current Limit

• Diodes have a maximum current limit
• Maybe 20 mA
• Do not connect an LED directly across a 5V supply
  • Too much current without a resistor

Lecture 2.3 Switches, Potentiometers

Switch/Pushbuttons

• Closing the switch completes the circuit
• Voltage on both terminals is identical when switch is closed

Potentiometer

• Three terminals: top, bottom, middle
• Resistance between top and bottom terminals is constant
• Ratio of resistances changes

Lesson 3

Lecture 3.1 Wiring

Interpreting a Schematic

• Shows how components are connected in real circuit
• You need to be able to build a real circuit from a schematic
• You need to be able to draw a schematic to represent your design

Solderless Breadboard

• Allows components to be easily connected in a non-permanent way
• Great for prototyping
• Holes fit 24 AWG solid wire
• Connected in rows of 5 holes and columns along the slides

Wiring Process

1. Select a hardware component

• Select one terminal on the hardware component
• Connect the terminal to a row of the breadboard
  • if the terminal needs to be connected to another terminal already in the breadboard, share the row
  • Otherwise, use a free row
• Go back to step 2 until all terminals are done
• Go back to step 1 until all components are done

Lecture 3.2 Wiring Demo, Pushbutton

Lecture 3.3 Wiring Demp, Potentiometer

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Week 2

Sensor Types
Pulse Width Modulation
analogWrite

Lesson 1

Lecture 1.1 Sensors

Sensors

• Allow the microcontroller to receive information about the environment
  • How bright is it?
  • How loud is it?
  • How humid is it?
  • Is the button being pressed
• Perform operations based on the state of the environment
• Turn on a light if it's dark out
  • Voice-controlled operation

Sensing the Environment

• Microcontrollers sense voltage
  • digitalRead(pin) returns state of a digital pin
  • analogRead(pin) returns the analog voltage on a pin
• Sensor logic must convert an environmental effect into voltage

Reading a Pushbutton

IoTM3W2L1.1.png

• Make a pin high when the button is pressed and low when it is not pressed
• Wrong circuit leaves pin open when not pressed

Lecture 1.2 Resistive Sensor

Resistive Sensors

IoTM3W2L1.2.png

• Many sensors change resistance
  • Photoresistor, thermistor, flex resistor,etc.
• Connect sensor in a voltage divider
• As resistance changes, voltage changes

Photoresistor

• As brightness increases, resistance decreases
• Resistance = 10K Ohms, voltage = 2.5 Volts
• Resistance = 5K Ohms, voltage = 3.33 Volts

Voltage-Controlling Sensors

IoTM3W2L1.2_2.png

• Some sensors control voltage directly
• Signal is pulled low when motion is detected
• Open-collector - signal floats without motion

Other Voltage Controlling Sensors

• Accelerometer reports acceleration in 3 dimensions
• Gyroscope reports angular velocity in 2 dimensions

Lecture 1.3 Resistive Sensor Demo

Lesson 2

Lecture 2.1 Actuators

Actuators

• Devices that cause something to happen in the physical world
• Outputs of the IoT device
  • Visual: LED,LCD, monitor
  • Audio: buzzer,speaker
  • Motion: motors, valve, pump
  • Tactile: heating, cooling

On-Off Actuation

• The only control is power
• Even complicated actuators can be controlled via power
  • LED, buzzer, monitor,etc.
• Does not use the full potential of the actuator
• On-Off control may be all that is necessary
  • Lights in a class room, air conditioning

Current Limits

• Watch out for current limits
• LED can only handle 20mA
  • Be sure to use an appropriate resistor
• Arduino can only supply 40 mA
  • Cannot drive a motor that requires 15 Amperes!
  • May need to use alternate power supply
  • Arduino can control access to power without providing power directly

Lecture 2.2 Analog Actuators

Analog Voltage Control

• Many actuators need an analog voltage for complete control
  • DC motor speed controlled by voltage
  • LED brightness controlled by voltage
  • Heating element temperature controlled by voltage
• Arduino cannot generate analog outputs

Digital to Analog Converter(DAC)

• DAC will convert digital number to an analog voltage
• Most microprocessors do not have a DAC
• Can buy one and attach it
• May be costly

Lecture 2.3 Pulse Width Modulation

Pulse Width Modulation

IoTM3W2L2.3.png

• Duty Cycle is the percent of time the pulse is high
• Increasing duty cycle increases perceived voltage

analogWrite()

• Generates a square wave on a pin, 490 Hz
• First argument is the pin number
• Second argument is the pulse width
  • 0 is 0% duty cycle
  • 255 is 100% duty cycle
• Pin number must be a PWM pin
  • Marked on the Arduino with the ~ symbol
• Ex. analogWrite(3,128);

Fade Example

int brightness = 0;
int fadeAmount = 10;
void setup() {
    pinMode(led, OUTPUT);
}
void loop() {
    analogWrite(led, brightness);
    brightness = brightness + fadeAmount;
    if (brightness == 0 || brightness == 255)
        fadeAmount = - fadeAmount ;
    delay(30);
    }        

Lesson 3

Lecture 3.1 Demo Fade Example

Lecture 3.2 Making Sounds

tone()

• tone() can generate a square wave with an arbitrary frequency
  • analogWrite() has fixed frequency
• Duty cycle is fixed at 50%
• Can be used to drive a speaker or buzzer
• Two or three arguments
  • Pin number
  • Frequency, in Hz
  • Duration in ms (optional)

Square Waves vs. Sine Wave

• Square waves sound bad
  • Many high-frequency components
• Square wave is the best we can do with digital outputs

Piezo Element, Buzzer

• Two inputs: signal and ground
• Produces a click when a rising edge is applied
• Driving with a square wave produces a pitch

Music System

void setup() {
}
void loop() {
    tone(8, 988, 1000);
    delay(1000);
    tone(8, 1047, 1000)；
    delay(1000);
}

• Plays two tones, 1 sec each
• Delay is needed; only one tone at a time

Lecture 3.3 Demo Music System

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Week 3

EEPROM Library
Wire Library
SPI Library
Servo Library

Lesson 1

Lecture 1.1 Arduino Libraries

Arduino Libraries

• Many devices are more complicated then simple sensors/ actuators
• Microcontroller (ATMega328) has components which are hard to use
  • Memories, communication interfaces, PWM logic, etc.
• Arduino provides libraries to facilitate their use
• Libraries are also available for external hardware
  • Wifi controller, LCD, GSM controller

EEPROM

• Electronically Erasable Programmable Read-Only Memory(EEPROM)
• Non-volatile memory; holds data without power
• Similar to Flash but more flexible
  • Write a single byte at a time
  • Supports many more write cycles
• Only 1024 bytes available on ATMega328

Reading and Writing

• Access one address at a time
• Each address contains one byte
• EEPROM.read(address) : returns the contents of an address
• EEPROM.write(address, data) : write a single byte of data into the address
• Address must be between 0 and 1023

Lecture 1.2 EEPROM

Reading and Writing

#include 
Void setup() {
    int addr;
    Serial.begin(9600);
    for (addr=0; addr<1024; addr++) {
        EEPROM.write(addr, addr);
    }
    for (addr=0; addr<1024; addr++) {
        Serial.print(EEPROM.read(addr), DEC)
    }
}

Multiple Bytes

• Can only read/write one byte at a time
• How do you deal with larger numbers?
  • Int is 2 bytes long
• Use masking to access a single byte at a time
• Mask is a series of bits that highlights the bits in the number that you are interested in
• Performing a bitwise and operation with the mask zeroes out run-interesting bits

Lecture 1.3 Masking

Masking

IoTM3W3L1.3.png

Masking High Bits

259>>8
(259>>8)&255

Writing an int to EEPROM

int bigData;
byte littleData;
void setup() {
    littleData = bigData & 0xFF;
    EEPROM.write(0, littleData);
    littleData(1, littleData);
}

Little Endian ordering

Lesson 2

Lecture 2.1 I2C Communication

I2C Communication Protocol

• Synchronous, serial protocol
• Multiple masters, multiple slaves
• Bitwidth is fixed, independent of number of slaves
• Two wires: SDA (serial data) and SCL (serial clock)
• Both lines are open-drain
  • Pulled up to high by default
  • State of bus is always known

I2C Terminology

• Master - Initiates and terminates transmission; generates Scl
• Slave - Addressed by the Master
• Transmitter - Placing data on the bus
• Receiver - Reading data from the bus

I2C Network

IoTM3W3L2.1.png

SDA and SCL are bidirectional

Lecture 2.2 I2C Transactions

I2C Transaction Structure

• Start Condition
  • Indicates the beginning of a transaction
• Address/Direction Byte
  • Specifies slave for communication
  • Specifies read vs. write transaction
• Data Byte(s)
  • Transmitted by either master or slave
• Stop Condition
  • Indicates the end of a transaction

Start and Stop Conditions

IoTM3W3L2.2.png

• Start Condition
  • Falling transition on SDA while SCL=1
• Stop Condition
  • Rising trasition on SDA while SCL=1

Lecture 2.3 Sending Bits

Sending a bit

IoTM3W3L2.3.png

• SDA is sampled by receiver on the rising edge of SCL
• SDA must be constant where SCL is high
  • Exception is Start/Stop Condition

Acknowledge Bit

IoTM3W3L2.3_2.png

• After each byte is sent, the receiver must acknowledge
• Transmitter releases SDA, receiver must pull SDA low
  • Must be low for one pulse of SCL
• If SDA is not pulled low, transmission is aborted

Typical I2C Transaction

IoTM3W3L2.3_3.png

• Each slave has a unique 7-bit address
• Direction bit: 0 indicates write, 1 indicates read

Lesson 3

Lecture 3.1 Wire Library

Wire Library

• The wire library is used to access I2C
• #include needed at the top
• Wire.begin()function initializes I2C hardware
• Calling Wire.begin() with no arguments makes the Arduino a Master
• Calling Wire.begin(addr) with an address makes the Arduino Slave

Master Communication

1. Start the transmission

• Send data

• End the transmission

  • Data is put into a buffer before sending
  • Wire.beginTransmission(address) : Start condition and address are initialized
  • Wire.write(data) : Buffers data for sending
  • Wire.endTransmission() :
    • Transmits data in buffer
    • Returns a status byte, 0 for success

Master Transmission Example

#define ADDR 1;
void setup() {
    Wire.begin();
    Wire.beginTransmission(ADDR);
    Wire.write(2);
    Wire.write(3);
    Wire.endTransmission(stop);
}

• Send two bytes
• Stop condition sent at the end

Lecture 3.2 Master Communication

Master Read

• Wire.requestFrom() : used to specify a read transaction
• Three arguments
  1. Address of the slave
  2. Number of bytes to read
  3. Optional stop argument to release the bus after
• Wire.read() : returns a single byte from the receive buffer
• Wire.available() : returns number of bytes waiting

Master Receiver Example

int sum = 0;
Wire.requestFrom(AddR, 2);
while (Wire.available())
    sum += (int) Wire.read();

• Receive two bytes from the slave, compute sum
• Wire.available() is used to check how much data is received

Lecture 3.3 Slave Operation

Slave Operation

• Slave must wait for a transmission, cannot initiate
• Busy wait loops are wasteful
• Callback functions: functions called when an event occurs
• Wire.onReceive() : identifies the function called when the slave receives data from a master (write transaction)
• Wire.onRequest() : identifies the function called when data is requested from the slave (read transaction)

typical Slave Receive Code

void receiveFunct(int byteMum) {
    int i, sum = 0;
    for (i=0; i

Callback must take one argument, number of bytes received

Typical Slave Transmit Code

void transmitiFunct(void) {
    Wire.write(SOME_DATA_BYTE);
}

Wire.onRequest(transmitFunct);

Callback must take no arguments, return nothing

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Week 4

About Arduino Shields
Arduino Shield List (Don't memorize, just reference)
Ethernet Shield
WiFi Shield

Lesson 1

Lecture 1.1 Arduino Shields

A Arduino shields

• shield : a printed circuit board (PCB) that adds functionality to your Arduino
• Hardware : A circuit is pre-wired and sold on a printed circuit board
• Software : A software library is provided to interact with the hardware

Benefits of Shields

• No wiring needed
  • Circuit is pre-wired
  • Connections to Arduino are fixed by stacking
• Simple to use
  • Library takes care of complicated details

Connected Pins

• Pins on the bottom of the shield connect to pins of the Arduino
• Most shields only use a small subset of the pins
• Need to know which pins are used when using multiple shields
• Shield headers may need to be soldered

Lecture 1.2 Ethernet Shield

Ethernet Shields

• Allow internet connections through a wired interface
• Shield includes an Ethernet jack (RJ45) for a network cable
• Several shields are available
• Common library is used

Internet Addresses

• Mac address : unique address "hardwired" into each network adapter. 6 bytes long
• IP address : address used for addressing by internet protocols. 4 bytes long
• Port : number identifying the application protocol being used. 2 bytes long

Domain Name Service

• Service that maps domain names to IP addresses
• Names are much easier to memorize than IP addresses
• DNS servers store the mapping
• Internet servers/clients may need to be configured with a DNS server

Lecture 1.3 Ethernet Library

Ethernet #include

• There are many .h files to include
  • Ethernet.h
  • EthernetClient.h
  • EthernetServer.h
• sketch-->Import; Library-->Ethernet

Initializing the Ethernet

• Invoke the Ethernet.begin() function
• 5 possible arguments, only the first is required
• MAC Address(required)
• IP Address
• DNS : Address of the domain name server
• Gateway : Address of a router which knows how to forward packets to other networks
• Subnet mask : Mask which specifies the local network(i.e. 2555.2555.255.0)

Dynamic Host Connection Protocol

• Every node on the internet needs an IP address
• DHCP allows the IP address to be assigned dynamically
• DHCP is invoked if Ethernet.begin() has no IP address argument
• Most routers are configured for DHCP
• static IP addresses are typical for servers

Lesson 2

Lecture 2.1 Ethernet Client

Ethernet Client

• Arduino can act as a client, create a client object
  • EthernetClient client;
• Needs to connect to a server
  • result = client.connect;
  • result = client.connect(domain, port);
  • Returns 1 if connection is made, 0 if it is not

Sending and Receiving Data

• client.print(data); and client.println(data); send data
• println() adds a carriage return data is a string or an array of bytes
• client.write(value); sends a raw byte
• data = client.read(); reads the next byte
• result = client.available(); returns 1 if data is waiting

Lecture 2.2 Client Examples

Client Sends Data

byte mac[]={0xDE, 0xAD, 0xBE, 0xEF, 0x12, 0x34};
char server[]= "testdomain.edu";
EthernetClient client;
void setup() {
    Ethernet.begin(mac);
    if (client.connect(server, 80)) {
        client.println("GET index.html HTTP/1.1");
        client.stop();
    }
}

• Sends a GET request to a web server
• Port 80 used for the web

CLient Receives Data

void loop() {
    if (client.available())
        Serial.print (client.read());
}

• Receives the response from the web server
• Sends data to serial monitor

Lecture 2.3 Ethernet Server

Ethernet Server

• Arduino can act as a server, create a server object
• EthernetServer server = EthernetServer(port);
  • Port argument is the port that the server listens to
• To start listening, server must create a client object EthernetClient client = server.available();
• client object will be false(0) if client is not available
• client.stop(); will close connection with client
• Use client.print() and client.write() to send data
• Use client.read() to read data

Server Receives Data

EthernetServer server = EthernetServer(80);
void setup() {
    Ethernet.begin(mac, ip, gateway, subnet);
    server.begin();
}

void loop(){
    EthernetClient client = server.available();
    if (Client) {
        Serial.print(client.read());
    }
}

Lecture 2.4 Ethernet Shield Demo

Lesson 3

Lecture 3.1 WiFi Shield

WiFi Shield

• Allows internet connections through a wireless interface
• IEEE 802.11 (WiFi) standard is used
• Library is similar to the Ethernet library

WiFi Initialization

• Wifi.begin(); -no arguments; just initializes the shield
• Wifi.begin(ssid); -connects to the network ssid
• Wifi.begin(ssid, keyindex, key); -connects to ssid with key as WEP password
  • WEP can have up to 4 keys
  • keyindex indicates which key to use

WiFi Client and Server

• Same as Ethernet client and server process
• WiFiClient:
  • WiFiClient client;
  • result = client.connect (ip, port);
  • client.stop();
• WiFiServer: slightly different
  • WiFiServer server(port);
  • Server.begin(); -starts server listening on port

Scanning WiFi Networks

• Which network(SSID) should you connect to?
• netnum = WiFi.scanNetworks(); -Returns the number of networks available
• ssid = WiFi.SSID(i); -Returns the SSID of the N°i network(-90 to 0)
• enc = WiFi.encryptionType(i); -Returns the encryption type used in the N°i network

Lecture 3.2 WiFi Shield Demo