[Mooc]IoT Course 4 Interfacing with the Raspberry Pi

Week 1

Reading Material

Lesson 1

Lecture 1.1 Network

Connecting to a Network

• Wired connection using the built-in RJ45 connector
• Wi-Fi connection using a USB Wi-Fi adapter

Wi-Fi Config

• start Wifi config from the desktop
• Allows you to select a network and give a password
• Similar to Mac OSX or Windows interface
• Click Scan to find networks
• Select the network you want
• DHCP is needed to get an IP address

Using a Web Browser

• Epiphany browser is built-in
• Icon on the desktop

Firewall Warning

• Your network may have a firewall
• To use a networked application, firewall must be set to allow that application's traffic
  • Web traffic may be allowed, but not World of Warcraft
• If you run a networked application and it doesn't work, check the firewall settings
  • Or ask the network administrator

Lecture 1.2 Secure Shell

Secure Shell

• Secure shell(ssh) allows you to access a machine remotely
• Two machines involved
  • ssh server - the machine you with to access remotely
  • ssh client - the machine which you use to access the server
• Commands you type into the client are executed by the server
• Text printed by the server appears on the client screen
• Basic ssh provides only a terminal interface
  • Not normally GUI

SSH Requirements

• Both machines must be on the Internet
• Must have an ssh client program on the client machine
  • Default on Linux, Mac OSX
• The machine being controlled must be running an ssh server
  • Default on Raspberry Pi
  • ssh server must be started on other machines
  • ssh server must be installed on Windows machines
• Must have an account on the server machine
  • Must provide username/password
• Any firewall must allow ssh access
  • Firewalls for client and server

Lecture 1.3 SSH Client/Server

Running the SSH Client

• Open a terminal(LXTerminal) and type the following command:ssh <username>@<domainname>
• <username> is your username on the server machine
• <domainename> is the address of the server machine
  • For example, uci.edu
• First time, you will get a message that the address could not be authenticated
  • Enter "yes" to continue, as long as you're sure of the address
• Enter password
• You will see the server's command-line prompt

SSH Client Screen Shot

Raspberry Pi SSH Server

• This is useful to access your Raspberry Pi without connecting it to a monitor/keyboard
• ssh server is running by default on your Raspberry Pi
• Should change the private host ID keys
  • Otherwise, they have the same default values

sudo rm /etc/ssh/ssh_host_* && sudo dpkg-reconfigure openssh-server

Lesson 2

Lecture 2.1 SSH Server

Getting Your IP Address

• Your Raspberry Pi does not have a domain name to serve as an address for client
• Need to get your IP address instead ifconfig

Accessing Raspberry Pi w/ SSH

• Using a Linux or Mac OSX machine with ssh pre-installed
• Using a terminal window
• Using the default "pi" account

Lecture 2.2 Network Programs

Programmatic Networking

• Accessing a network manually is easy
• We want to access to network via a program
• Enable interaction between the network and he world
• What IoT is about

Internet Structure

A hierarchy of local area networks(LANs) connected by routers

• Also switches and bridges

IoTM5W1L2.2.png

Internet Protocols

• Need to send data between incompatible networks
• A protocol is a set of rules defining
  • how data should be transferred
  • what data is contained in each packet
• Every machine in the network must implement a common set of protocols to communicate on the Internet
• Internet protocols do not interfere with LAN protocols

Lecture 2.3 Internet Protocols

Key Features of Internet Protocols

• Unique naming
  • Defines a format for host addresses
  • Each node gets one unique host address
• Message structure
  • Defines a standard transfer unit, a packet
  • Packet consists of header and payload
    • Header: protocol information(i.e. destination address)
    • Payload: contains data to be transmitted

Internet Protocol Family

• IP (Internet protocol)
  • Host naming scheme
  • Host-to-host connection, unreliable
• UDP (Unreliable Datagram Protocol)
  • Process-to-process communication
  • Process naming
  • Also unreliable
• TCP (Transmission Control Protocol)
  • Process-to-process communication and naming
  • Process naming
  • Reliable communication

TCP vs. UDP

• TCP and UDP are the transport layer protocols
• TCP is connection-oriented
  • Reliable, will resend a lost or corrupted packet
  • Packet sequencing supported
  • Flow control, error detection/correction
• UDP is connectionless
  • Unreliable, does not guarantee packet arrival
  • Simpler, faster, smaller than TCP

Lesson 3

Lecture 3.1 IP Addresses

IP Addresses

• TCP/IP addresses a machine using an IP address
• A unique number for all machines on the internet
• IP version 4(IPv4) uses 32-bit addresses
  • Four numbers (8-bits each) separated by periods -- 192.0.0.0
• Network Address: High bytes of IP address common across an entire LAN/WAN
• Host Address: Low bytes of IP address unique for each machine in a network

IPv6

• IPv4 uses 126-bit addresses compared to 32-bits with IPv4
• IPv4 only supports 2^32 addresses
  • Internet will exceed this number
• IPv6 integrates security
  • IPSec used to encrypt data in transit
• IPv6 incorporates several changes to the header
  • Some fields become optional
• IPv6 is not widely adopted yet

Ports

• TCP and UDP use ports to address specific applications on a machine
• Port numbers are assigned to each networked application layer protocol
  • Ex. HTTP uses port 80
    • Web browser sends page requests on port 80
    • Web server listens to port 80 for requests
• Port number is 16-bit value in TCP and UDP headers

Lecture 3.2 Domain Names

Host Names & Domain Names

• Each host on the Internet has a unique IP address
  • 128.2.203.179
• IP addresses are not easy for humans to memorize, so we use domain names
  • ics.uci.edu, cnn.com
• Each domain name must be resolved to an IP address to send packets

Domain Naming System (DNS)

• DNS is a hierarchical naming system used to determine IP addresses from domain names
• Gigantic, distributed tables are accessed by performing a DNS Lookup
• IP addresses are stored in a local cache to save time

nslookup

Program that performs a DNS lookup and returns the IP address

Lecture 3.3 Client/Server

Client-Server Model

IoTM5W1L3.3.png

• Networked applications commonly use the client-server model
• Server manages a resource
• Server accepts requests, sends responses

Internet Connections

• Clients and servers communicate over connections
• A socket is an endpoint of a connection
• Client and server both have sockets
• A port is a 16-bit integer that identifies a process:
  • TCP and UDP use ports to refer to processes
  • Some ports are well-known and associated with an application(e.g., port 80 is associated with Web servers)

Ports and Servers

IoTM5W1L3.3_2.png

• Multiple clients and servers can exist on the same machine
• Server processes listen to their assigned ports
• Client processes send requests on their assigned ports

Week 2

Reading material

Lesson 1

Lecture 1.1 Sockets

Sockets Interface

• Programming interface to perform network communication
• Can be used in many languages
  • We will use Python
• Based on client/server programming model

Sockets on the Client

Creating a generic network client:

1. Create a socket
2. Connect socket to server
3. Send some data (a request)
4. Receive some data (a response)
5. Close the socket

Creating a Socket

import socket

mysock = socket.socket(socket.AF_INET,socket.SOCK_STREAM)

• Need to import the socket package
• socket.socket() creates the socket
• AF_INET declares Address Family Internet
• SOCK_STREAM indicates TCP (connection-based)

Lecture 1.2 Sending Data

Connect Socket to Server

host = socket.gethostbyname("www.google.com")
mysock.connect(host, 80)

• Need a host to connect to
• Host is an IP address, but you may only have the domain
• gethostbyname() performs DNS lookup
• connect() creates the connection
• Port is second argument, 80 is web traffic

Sending Data on a Socket

message = "GET / HHTTP/1.1\r\n\r\n"

mysock.sendall(message)

• Message string is an HTTP GET request
  • could send any data
• sendall() send the data
  • Tries until it succeeds

Receiving Data on a Socket

data = mysock.recv(1000)

• recv() returns data on the socket
  • Blocking wait, by default
• Argument is the maximum number of bytes to receive

Closing a Socket

mysock.close()

• Close connection, free up port

Lecture 1.3 Exceptions

Errors During Execution

• Errors may happen when working with sockets
  • Socket cannot be opened
  • Data cannot be sent
• Errors occurring during execution are called Exceptions
• There are many kinds for each function
  • ZeroDivisionError
  • TypeError

Handling Exceptions

• When an error happens, you might want your code to do something appropriate
• Use try and except statements
• Place code with possible error inside the try clause
• Code in the except clause is executed when an exception occurs

try:
  z = x / y
except ZeroDivisionError:
  print("Divide by zero")

Socket Exceptions

• socket.error
  • All socket errors
• gaierror
  • getaddressinfo() error - no host found
• We will handle some of these to make the networking more robust to errors

Client Program

import socket
import sys

try:
    mysock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
except socket.error:
    print("Failed to create socket")
    sys.exit()
try:
    host = socket.gethostbyname("www.google.com")
except socket.gaierror:
    print("Failed to get host")
    sys.exit()
mysock.connect(host, 80)
message = "GET / HTTP/1.1\r\n\r\n"
try:
    mysock.sendall(message)
except socket.error:
    print("Failed to send")
    sys.exit()
data = mysock.recv(1000)
print(data)
mysock.close()

Lesson 2

Lecture 2.1 Server Code

Sockets on the Server

Server needs to wait for requests

1. Create a socket
2. Bind the socket to an IP address and port
3. Listen for a connection
4. Accept the connection
5. Receive the request
6. Send the response

Creating and Binding a Socket

mysock = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
mysock.bind("",1234)

• bind() binds the socket to a port
• First argument is the host, it is empty
  • Can receive from any host
• Port number is arbitrary and not well-known

Listening and Accepting a Connection

mysock.listen(5)
conn, addr = mysock.accept()

• listen() starts listening for a connect()
  • Argument is backlog, number of requests allowed to wait for service
• accept() accepts a connection request
  • Returns a connection (for sending/receiving) and an address (IP, port)

Lecture 2.2 Live Server

Sending and Receiving

data = conn.recv(1000)
conn.sendall(data)

conn.close()
mysock.close()

• recv() and sendall() used to send and receive data
• Connection and socket closed separately

A Live Server

while True:
    conn, addr = mysock.accept()
    data = conn.recv(1000)
    if not data:
        break
    conn.sendall(data)
    
conn.close()
mysock.close()

• An infinite loop is typical
• Connection closed when no data is received

Full Server Program

import socket
import sys

mysock = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
try:
    mysock.bind("",1234)
except socket.error:
    print("Failed to bind")
    sys.exit()
mysock.listen()
while True:
    conn, addr = socket.accept()
    data = conn.recv(1000)
    if not data:
        break
    conn.sendall(data)
    
conn.close()
mysock.close()

Lecture 2.3 Internet Control

Control via the Internet

• Controlling a device over the Internet is interesting
  • Home automation
  • Tele-medicine
• Send commands to a Raspberry Pi
• RPi does something in the real world
• Sensor data can be sent remotely also

Internet Controlled LED

• LED turns off and on by remote commands
• Send "on" message to turn LED on
• Send "off" message to turn LED off
• Modify server program to control LED

Modified Server Program

while True
    conn, addr = mysock.accept()
    data = conn.recv(1000)
    if not data:
        break
    if data == b'on':
        GPIO.output(13,True)
    if data == n'off':
        GPIO.output(13,False)

• Receive data is compared to commands
• Data is a byte array, not a string

Lesson 3

Lecture 3.1 Python Client Demo

Lecture 3.2 Python Server Demo

Week 3

Reading Material 1

Reading Material 2

Lesson 1

Lecture 1.1 Network Libraries

Networking Libraries

• The Socket library is very low level
• Programmer composes the message content
• Must know details of the protocol

Protocol-Specific Libraries

• Other libraries are available for specific protocols
• Programmer does not need to know protocol details
• Library functions are provided to handle details

import http.client
conn = httplib.HTTPConnection("www.google.com")
conn.request("GET","/")

Interaction with Online Services

• Many services exits which you can use programmatically
  • Google Maps
  • Twitter
  • YouTube
  • Facebook
• Your program can use these services
  • You may need to pay for access

Lecture 1.2 Web Services

Web-based Services

• Services "in the cloud"
• Runs on remote server, accepts requests from clients
• Interact using HTTP messages

Application Programming Interface

• An API defines the communication interface between programs
• Defines the format of Request/Response messages
• Defines legal message sequences

GET /maps/<place> HTTP/1.1

Software Development Kit(SDK)

• An SDK is set of tools to support the use of an API
• Typically library functions
• Programmer does not need to know the message details
• API and SDK may be used interchangeably

API:

GET /maps/<place> HTTP/1.1

SDK:

map = GetMap("UCI")

Lecture 1.3 Public APIs

Example API for Sentiment Analysis

• Sentiment analysis analyzes text to determine if it is positive or negative
  • "I hate cats" score =-1
  • "I love cats" score =+1
• AlchemyAPI (owned by IBM) does this
• Can download their SDK and use their API
  • May not work on Raspberry Pi

AlchemyAPI SDK

• Want to can a web page and check its sentiment
• Webpage is written in HTML

from alchemyapi import AlchemyAPI

demo_html = '<html><body>AlchemyAPI works on HTML </body></html>'

response = alchemyapi.sentiment('html' , demo_html)

if 'score' in
response['docSentiment']:
    print('score: ',response['docSentiment']['score'])

Lesson 2

Lecture 2.1 Twitter's API

Twitter's API

• Raspberry Pi can run several SDKs for Twitter's API

• RPi can respond to tweets

  • May look for a tag

• Twython is the package we will use

• Installing Twython

  sudo apt-get update
  sudo apt-get install python-pip
  pip install twython
  

• Pip is an installer for Python packages

Registering Your Twitter App

• Your app needs to be registered to access Twitter's API
  • Need a twitter account first
• You will receive several keys needed for authentication
• Twython functions use keys to transmit messages
• Twitter servers authenticate if keys are correct
• Go to http://apps.twitter.com
• Click the Create New App button

Lecture 2.2 Twitter Registration

Create an application

• Any website is fine
• Click Create Twitter Application button at bottom

Application Details

• Details of app are shown
• Consumer Key will be needed
• Go to Keys and Access Tokens

Keys and Access Tokens

• Record Consumer Key and Consumer Secret
• Click Create my access token at bottom

Access Tokens

• Record Access Token and Access Token Secret

Lecture 2.3 Sending a Tweet

Sending a Tweet

• Use the keys to create the Twython object

  from twython import Twython
  C_KEY = "?????????"
  C_SECRET = "?????????"
  A_TOKEN = "?????????"
  A_SECRET = "?????????"
  
  api = Twython(C_KEY, C_SECRET, A_TOKEN, A_SECRET)
  api.update_status("Hi")
  

  Searching for a Hashtag

  • Maybe we want the Raspberry Pi to react to a hashtag
  • When the hash tag appears, do something
  • Need to scan the Twitter stream for the hashtag

  Twython Streamer

  • A TwythonStreamer object allows you to examine public streams

  • TwythonStreamer has a method which searches for text in streams, statuses.filter()

  • Pass as an argument the terms you want to track

  • i.e.

    stream.statuses.filter(trach='Harris')
    

    ​

Lecture 2.4 Sending a Tweet(Demo)

Lesson 3

Lecture 3.1 Twython Callbacks

Using TwythonStreamer

• First, define a new class which extends TwythonStreamer
• class MyStreamer(TwythonStreamer):
• This allows you to redefine some of the methods of TwythonStreamer
• Define a method on_success()inside your class
• on_success()is a callback
  • Called when a tweet is found matching your criteria

on_success() callback

def on_success(self, data):
    if 'text' in data:
        print("Found it.")

• data is a dictionary passed to on_success()
• text field of data is the matching tweet

Lecture 3.2 Tweet Response

Filtering Twitter Streams

class MyStreamer(TwythonStreamer):
    def on_success(self, data):
        if 'text' in data:
            print("Found it.")
stream = MyStreamer(C_KEY, C_SECRET, A_TOKEN, A_SECRET)
stream.statuses.filter(track = "Harris")

• Create the MyStreamer class
• Callback prints a result
• Instantiate MyStreamer
• Filter the stream to find the text

Blinking in Response to a Tweet

def blink():
    GPIO.output(13, GPIO.HIGH)
    time.sleep(1)
    GPIO.output(13, GPIO.LOW)
    
class MyStreamer(TwythonStreamer):
    def on_success(self, data):
        if 'text' in data: 
            blink()

• Let's make an LED blink when a tweet is received

Lecture 3.3 Responding to a tweet(Demo)

Week 4

camera module setup

camera readme

camera python readme

Lesson 1

Lecture 1.1 Camera Module

Raspberry Pi Camera Module

• Camera are useful sensors
• There are many cameras that can be used with Raspberry Pis (USB)
• The Raspberry Pi camera module is useful
  • Camera Serial Interface (CSI) to the processor
  • Good libraries for control

Enabling the Camera

• Use raspi-config to enable the CSI Interface

  ​ sudo raspi-config

• Select Enable Camera, Finish

• Reboot the RPi

Lecture 1.2 picamera Library

python-picamera Library

• Install the library

sudo apt-get update
sudo apt-get install python3-picamera

• Using the library

import picamera

• Instantiate an object of the PiCamera class

camera = picamera.Picamera()

Camera Functions

• Take a picture

camera.capture("pict.jpg")

• Changing camera settings
  • There are many

camera.hflip = True
camera.vflip = True
camera.brightness = 50
camera.sharpness = 0

• View video on RPi screen

camera.start_preview()
camera.stop_preview()

Video Recording

import picamera
import time

camera.start_recording("vid.h264")
time.sleep(10)
camera.stop_recording()

Lecture 1.3 Capturing Images

Sending an Image on the Network

• What if you want to a remote site?
  • Home security system
• Capture an image, send it on a connection

mysocket = socket.socket()
mysocket.connect(('aserver', 8000))
conn = mysocket.makefile('wb')
camera.capture(conn,'jpeg')

• Need a file-like object to capture to

TImelapse Rhtography

• camera.capture_connections() takes photos over time
• Takes one argument, a file name
• {counter}and timestamp can be substituted
• ex.picture{counter}.gpg produces picture1.jpg, picture2.jpg,etc

Continuous Capture

camera = picamera.Picamera()
    for filename in
        camera.capture_continuous(img(counter),jpg)
            time sleep(300)

• Iterate through all images
  • Infinite loop
• 5 minute delay between images

Lesson 2

Lecture 2.1 Camera(Demo)

Lecture 2.2 PWM on RPi

Pulse Width Modulation

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

Servo Motors

• Motors whose rotation angle can be precisely controlled
• Pulse width controls rotation angle
  • 50Hz frequency is normal
  • 1.0 ms width = 0 degrees
  • 2.0 ms width = 180 degrees
• Same interface is used for remote control
  • Receiver sends PWM to control interfaces

Lecture 2.3 Servo Control

Servo Motor Wiring

• Three wires:
  • Power (Red)
  • Ground (Black)
  • Signal (White or Yellow)
• PWM applied to signal wire
• Power should supply sufficient current

Servo Motor Power

• External power supply should be used
  • ~5 volts
• Raspberry Pi cannot supply enough current to drive typical motors
  • ~1 Amp
• External supply has power and ground wires
  • Wire external power wire to Servo power wire
  • External ground wired to Raspberry Pi ground

Servo Wiring

IoTM5W4L2.3.png

• Only pins 12 and 24 (BOARD numbering) can produce PWM signals
• Resistor might be used to isolate pins from servo

Lesson 3

Lecture 3.1 Servo Code

Servo Scan Code Example

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BOARD)
GPIO.setup(12, GPIO.OUT)
pwm = GPIO.PWM(12, 50)
pwm.start(0)
foreach i in range(100):
    pwm.ChangeDutyCycle(i)
    time.sleep(0.1)
foreach i in range(100, 0, -1):
    pwm.ChangeDutyCycle(i)
    time.sleep(0.1)

Lecture 3.2 Servo (Demo)