[Mooc]IoT Course 4 The Raspberry Pi Platform and Python Programming for the Raspberry Pi

Week 1

Reading Material

Lesson 1

Lecture 1.1 Raspberry Pi Board

Raspberry Pi Hardware Specs

Broadcom BCM2836 SoC
- 900Mhz, 1Gb RAM
Dual Core VideoCore IV Multimedia Co-Processor
- GPU
40 GPIO pis
- only 26 on Raspberry Pi A and B
4 USB ports
- only 2 on the Raspberry Pi B
Micro SD card slot
- full-sized SD card slot on previous Raspberry Pi

Raspberry Pi B+

IoTM4W1L1.1.png

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Lecture 1.2 Raspberry Pi Processor

ARM Processors

ARM licenses : Intellectual property
Silicon vendors build System-on-Chip(SoC) designs using ARM IP
15+ silicon vendors use ARM

ARM Processor Family

Broadcom BCM2836 SoC is ARM Cortex A7

Lecture 1.3 Raspberry Pi vs. Arduino

Raspberry Pi vs. Arduino

Raspberry Pi processor is faster
- 900MHz vs 16MHz
32-bit processor vs. 8-bit
- Bigger address space, number representations
Raspberry Pi has more memory
- Arduino: 32K Flash, 2K SRAM, 1K EEPROM
- Raspberry Pi: 512K SRAM, 4G Flash, micro SD
Raspberry Pi has lower I/O voltage levels
- 3.3V vs. 5V

Using an Operating System

Raspberry Pi can support an operating system
Enables a range of features

Lesson 2

Lecture 2.1 Operating System Benefits

User Interface

Text-based interface : Type commands directly into text-based console
Graphic interface : Use point-and-click interface

File System

Can create and modify files in a directory structure
Similar to other file system interfaces

Lecture 2.2 Processes

Multiple Processes

Can download and run multiple programs
Can execute many processes concurrently

Using Hardware Devices

User Application : Any application running in user space
/dev/xxx : File associated with a hardware device
Device Driver : Concert file accesses t device accesses; enable apps to access arbitrary hardware devices
HW device : keyboard, monitor, etc.

Lecture 2.3 Raspberry Pi IoT

Is Raspberry Pi and IoT Device?

Maybe - Depends on how it is used
Similarities

Network connectivity and computational intelligence
Small and cheap (relative to a PC)
Can interface directly with sensors/actuators via pins

Differences

Interface can be exactly the same as PC running Linux
- Complexities of the system can be visible

Lesson 3

Lecture 3.1 Raspberry Pi Setup

Setup of the Raspberry Pi

Step1 : Plug in a monitor(via HDMI) and a keyboard and mouse (via USB)

Need an interface to the device

Step2 : Get an operating system

Raspberry Pi needs an operating system
Operating system image must be present on the micro SD card

Installing an Operating System

use New Out-Of-Box Software(NOOBS)

Comes preinstalled on micro SD bundled with Raspberry Pi boards
Otherwise, download it for free from www.raspberrypi.org/downloads
If NOOBS is not preinstalled on micro SD, you'll need to:
1. Format the micro SD (need an SD reader)
2. Extract the NOOBS downloaded
3. Put it on the micro SD

NOOBS

NOOBS will install an operating system on your micro SD card
You get a choice of the OS
- Short list if you have no network access; long list otherwise
Choose Raspian (a Linux distribution), the default option

Lecture 3.2 Raspberry Pi Configuration

Raspi-Config

raspi-config is a tool which lets you setup various setup/boot options for the Raspberry Pi
raspi-config will run automatically when you boot the Raspberry Pi with a new micro SD card for the first time

Raspi-Config Options

Expand Filesystem - Reformats your micro SD card filesystem to allow access to all the memory
Change User Password - Raspberry Pi starts with one user account(username: "pi") with a default password ("raspberry")
Enable Boot to Desktop/Scratch
- Console is default boot option
- Desktop is the graphic interface
- Scratch is a programming environment for kids
- Desktop may not be necessary
Internationalisation and Rastrack
- Internationalisation Options
  - Change Locale - Select a language
  - Change Timezone
  - Change Keyboard Layout
    - QWERTY is default
- Add to Rastrack
  - Service that allows Raspberry Pi users to find one another
  - Totally optional
  - Approximate location based on IP address

Lecture 3.3 Overclocking

Overclocking

Overclocking refers to increasing the clock frequency of the device, beyond the recommended frequency
Overclocking may also refer to increasing the internal voltage levels to increase speed
There are several different clocks inside a typical device
- ARM frequency: clock driving the ARM processor core
- SDRAM frequency: clock driving memory

Impact of Overclocking

Instructions are executed more quickly
- Roughly one instruction per clock period
Signals have shorter time in which to travel
- Signals must travel between storage elements in a single clock period
- signal data may not reach destination in time
Temperature of device increases
- Shortens device lifetime

Impact of Increasing Voltage

Increased voltage swing may increase transistor speed
Power consumption in proportional to V²
Thermal effects may alter timing

Week 2

Reading material

Lesson 1

Lecture 1.1 Linux Basics

The Shell

Interprets user input and executes commands
Text-based user interface of an operation system
bash (bourne again shell) is the default shell for Raspian
Gives more precise control to the user
Requires memorization for efficiency

Console or Terminal

The console or terminal is a text entry and display device
- Used to be a physical device (vt100 terminal)
- Virtual consoles are typical now
LXTerminal is the terminal used in Raspian

Lecture 1.2 Login

Accounts

There can be many user accounts on a Linux system
Each account has a username and password for identification
When you first start the machine, you are prompted for username and password
Default username is "pi", password is "raspberry"

Man(ual) Pages

"man" give information about a Linux command

Lecture 1.3 Linux Filesystem

The Filesystem

IoTM4W2L1.3.png

Hierarchy of directories and files

PWD

Lesson 2

Lecture 2.1 Navigating the Filesystem

CD

To a specific directory
Up or down one level

ls

Show the contents of a directory
- Files and other directories
-l option shows all detail

Mkdir, Rmdir

mkdir creates a directory
rmdir removes a directory
rmdir only works if directory is empty

Lecture 2.2 Text Editors

Creating Files

Many ways to do this, depending on the type of file you want to create
Typical method involves a text editor
- Like a word processor but simpler
Several are available on Linux for free
- Emacs, vi, vim, etc.
Choose a favorite and stick with it

Nano

Run it by typing "Nano" at the prompt
Basic functions via control sequence

Lecture 2.3 Accessing Files

Viewing a File

"cat" prints the file to the terminal
"head" prints the first 10 lines
"last" prints the last 10 lines

CP

Make a copy of a file

MV

Move a file
Rename it or move it to a new directory

Lesson 3

Lecture 3.1 Permissions

File Permissions

Files have owners
- User who created the file
Files have access permissions
- Read (r), write(w), execute(x)
Different permissions can be assigned according to type
1. User: the file owner
2. Group: a permission group
3. Other: all users

Viewing File Permissions

Root Account

THe root account has highest permission level
Key files and directories are only accessible by root
Sometimes you need root privileges
- Install a program
- Change the operating system
Use the "sudo" command to gain root permission for a single command

Lecture 3.2 Processes

Processes

A process is the execution of a program
Linux allows multiple processes to run concurrently
- Foreground vs. background
User can do something while other tasks are taken care of
- Read email
- Download file
- Wait for network connection
- check for viruses

Viewing Processes

Each process has a unique PID
"kill" can be used to end a process

Shutdown

Should not just unplug a Linux machine
Proper shutdown procedure is needed to place data structures in a good state
- Flush all buffers, close files, etc.
Use the "shutdown" command

Lecture 3.3 Linux Graphic User Interface

Using the GUI for Raspian

After initial login, type "startx"
Initiates the X Windows system with a default window manager
The manager determines the look

File Manager

Allows easy file access

Week 3

Reading Material

Lesson 1

Lecture 1.1 Python on Raspberry Pi

Raspberry Pi for IoT

Raspberry Pi can be used as a laptop/desktop
To use it as part of an IoT device, programming is needed
Many languages can be used
- Need a compiler (C, C++, Java, etc.) and an interpreter (Java, Python, Perl, tec.)
Python is most convenient
- Good programming environment built-in
- Good APIs available to access Raspberry Pi hardware

Python Language

High-level language, easy to use
- Do not need to explicitly declare data types
- No pointers
- Object-oriented programming, classes
Slow compared to C, C++
- Interpreted, not compiled
Two versions: Python 2.x and Python 3.x
- Python 2.x is still supported
- Programming differences are small
- Will use Python 3.x

Lecture 1.2 Python Programming Environment

Python Programming Environment

Two possible environments:

Integrated Development Environment(IDE)
- IDLE is the best option
- Invoke via Menu > Programming > Python
- Select Python 2 or Python 3 (use 3 for now)
Text editor and interpreter, separately
- Use Pico or Nano to write a program, "test.py"
- Execute program by typing "python3 test.py"

Executing Python Code

Two ways to do it:

Interactive: execute lines typed interactively in a Python console.
Batch: execute an entire Python program
- Interactive execution requires a Python shell
  - Start IDLE, shell s default
  - In terminal, type "python3"

Executing Programs from IDLE

Start IDLE
File > New File to create a new text editor window
Type in code
Select Run > Run Module
Python shell will open and code will execute

Lecture 1.3 Python Expressions

Algebraic Expressions

Python shell can evaluate algebraic expressions
Many algebraic expressions
- abs()
- min()
- max()

Boolean Expressions

Evaluate to True or False
Often involve comparison operators <, >, ==, !=, <=, and >=

Boolean Operators

Evaluate to True or False
May include Boolean operators and, or, not

Variables, Assignments

Variable types are not declared
Interpreter determines type by usage

Lesson 2

Lecture 2.1 Strings

Strings

A sequence of characters enclosed in quotes 'Hello, world'
Can be assigned to a variable
Can be manipulated using string operators and functions

String Operators

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Indexing Operator

Index of an item in a sequence is its position in the sequence
Indexing operator is [], takes an index as argument
Indices start at 0
Can be used to identify characters in a string

Lecture 2.2 Functions

Defining Functions

A sequence of instructions associated with a function name
Function definition starts with def
Followed by function name, open/close parentheses, and colon

>>> def test():
     print('A test function')

>>> test()
A test function
>>>

Defining/Calling Functions

All instructions in a function definition are indented
- IDLE does this automatically
Function is called by typing function name with parentheses after it

Lecture 2.3 Function Arguments

Function Parameters/Arguments

A function can take arguments which are values bound to variables inside the function
Argument are listed between parenthesis in the function call

>>> def circle_area(rad) :
      print(3.14 * rad * rad)
>>> circle_area(2)
12.56

Function Return Values

Functions can return values with the return instruction
A function call is substituted for its return value in an expression

>>> def circle_area(rad) :
      return 3.14 * rad * rad
>>> circle_area(2)
12.56
>>> 3 + circle_area(2)
15.56
>>>

Lesson 3

Lecture 3.1 Lists

Lists

A comma-separated sequence of items in square brackets
Items can be numbers, strings, other lists, etc.

>>> pets = ['ant', 'bat', 'cod', 'dog']
>>> lst = [0, 1, 'two', [4, 'five']]
>>> nums = [0, 1, 2, 3, 4]
>>>

List Operators and Functions

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Lecture 3.2 Lists Methods

List Methods

List operators that are called on the list that they operate on

>>> lst = [1, 2, 3]
>>> lst.append(8)
>>> lst
[1, 2, 3, 8]

IoTM4W3L3.2.png

append(), remove(), reverse(), and sort() do not return values
They only modifier the list

Lecture 3.3 Control Flow

Control Flow

Statements that change the order in which lines or code are executed

if statement
for loop
while loop

If statement

Template:

if <condition>:
    <indented code block>
<non-indented statement>

Example:

if temp > 80:
    print('It is hot!')
print('Goodbye.')

If-else statement

Template:

if <condition>:
    <indented code 1>
else:
    <indented code 2>
<non-indented statement>

Example:

if temp > 80:
    print('hot!')
else:
    print('not hot.')
print('Goodbye.')

For Loop

Executes a block of code for every element in a sequence
Variable is bound to a sequence element on each pass

>>> name = 'Ian'
>>> for char in name:
     print(char)
I
a
n
>>>

For Example

Any sequence can be used
All code in loop must be indented

>>> for name in ['Jon', 'Mary', 'Pete']:
     print(name)
Jon
Mary
Pete
>>>

While Loop

Execute indented block of code while condition is True

>>> i = 0
>>> while i < 3:
     print(i)
     i = i + 1
0
1
2
>>>

Week 4

Reading material

Lesson 1

Lecture 1.1 General Purpose IO Pins

GPIO Pins Raspberry Pi B+

IoTM4W4L1.1.png

Dedicated power and ground pins
3.3V(1,17), 5V(2,4),Gnd(6,9,14,20,30,39)

General Purpose/Multi-Function

Pins labeled "GPIOxx" can be used as general purpose I/O
Some pins are multi-function
- Extra label

UART Pins

Pins 8 and 10 can be used for UART(serial) communication
TX for transmission
RX for receiving

Lecture 1.2 Protocol Pins

I2C Pins

Pins 3 and 5 can be used for I2C communication
SDA for data
SCL for clock

SPI Communication Pins

MOSI(19), MISO(21), SCLK(23)
2 pins for chip enable, CE0(24) and CE1(26)

Lecture 1.3 GPIO Access

GPIO Access in Python

Use the GPIO library
import Rpi.GPIO as GPIO
Execute your Python program (script) as root
- Use "sudo" for this

Pin Numbering Modes

Two ways to refer to the pins

The number of the pins in their order on the board
- Shown in circles in the picture
The Broadcom SoC number
- Shown in rectangles, after "GPIO"

Selection Pin Numbering Mode

GPIO.setmode(GPIO.BOARD)

Use board numbering

GPIO.setmode(GPIO.BCM)

Use Broadcom SoC numbering
Changes with different versions of Raspberry Pi

Lesson 2

Lecture 2.1 General Purpose IO Pins

Pin Direction and Assignment

GPIO.setup(13, GPIO.OUT)

Set the pin direction
Like pinMode(13,OUTPUT) for Arduino

GPIO.setup(13, GPIO.OUT)

Assign value to output pin
Like digitalWrite(11,HIGH) for Arduino

Blink an LED

import Rpi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BOARD)
GPIO.setup(13, GPIO.OUT)
while True:
    GPIO.output(13, True)
    time.sleep(1)
    GPIO.output(13, False)
    time.sleep(1)

Reading Input Pins

GPIO.setup(13, GPIO.IN)

Set the pin direction to an input

value = GPIO.input(13)

Read value on input pin
Only reads digital inputs
- No analogRead equivalent
- No analog-to-digital converter

Lecture 2.2 Pulse Width Modulation

Pulse Width Modulation

PWM functions in GPIO library

PWM Initialization

pwm_obj = GPIO.PWM(18, 400)

Mark pin for PWM
Second argument is frequency

pwm_obj.start(100)

Start generating PWM signal
Argument is duty cycle, 0 to 100

PWM Control

pwm_obj.ChangeDutyCycle(50)

Assign new duty cycle
PWM frequency is not accurate
- Off by over 50% at 10 kHz

Frequency Control

Cannot easily control frequency
- No tone() function as on Arduino
Need to do it manually

While True:
    GPIO.output(18, True)
    time.sleep(0.5)
    GPIO.output(18, False)
    time.sleep(0.5)

1Hz frequency

Lecture 2.3 Demo of a Blink

Lesson 3

Lecture 3.1 Graphic User Interface

Graphic User Interface

Can use a GUI to access the GPIO
Raspberry Pi does it ... Arduino doesn't
- GUIs are supported by the operating system
Various visual entities (widgets) you can interact with
- Buttons, menus, sliders, scrollbars
- Drawing surfaces for drawing
Execution is controlled by the user, not the programmer
- File opened when "open" button is clicked

Event Loop

Typically, program will wait for the user to activate one of its widgets
- Push a button, select a menu item, draw on a drawing surface etc.
Do something in response
Then wait for you to do something else

Lecture 3.2 Tkinter Library

Tkinter

Tkinter library provides tools for writing programs that use graphics:
- many GUI widgets
  - buttons, menus, labels, scrollbars, etc.
- a canvas widget on which arbitrary drawing can be created
  - using lines, circles, rectangles, ovals, images, text, etc.

from Tkinter import *
root = Tk()
root.geometry('800x600')
c = Canvas(root, width=800, height=600)
c.pack()
r = c.create_rectangle(0, 0, 50, 50, fill='red', outline='red')

Opens a window with a red rectangle in the corner

Lecture 3.3 Interaction

Scale Widget

from Tkinter import *
master = Tk()
w = Scale(master, from_=0, to=100, orient=HORIZONTAL)
w.pack()

Draws a scale widget
Slider can be moved by the user

Interacting with the Widget

Want to do something when the user moves the slider

w = Scale(master, from_=0, to=100, orient=HORIZONTAL, command = update)

def update(duty):
    pwm.ChangeDutyCycle(float(duty))

Update function is called
Takes the slider value as an argument