A 2 day tutorial with hands-on exercises

held during AFNOG 2018 in Dakar, Sénégal

Uli Raich (uli.raich@gmail.com)

Typical applications where:

• Email
• Remote login
• File transfers

With cheaper and more powerful micro-controllers devices can communicate with each other

or with centralized servers over the network and they can observe their environment

with dedicated sensors.

This is what we call the Internet of Things (IoT)

containing just a single CPU and address and data lines + a few control lines to interface

to external memory and I/O interfaces, typically : a serial and a parallel port.



The price for the chip was 176 US $.

The development board was sold for 300 US $.

You got 256 bytes of RAM, 2kBytes of EPROM and the serial and parallel port.

Programming was done in assembly language or even straight machine code.

No Internet!

The user community is huge and is now increased by another 15 users!

An enormous wealth of information on all sorts of subjects using the Raspberry Pi

can be found on the WEB.

The official site is

https://www.raspberrypi.org

TWiki uses the same documentation format as Wikipedia.

This makes it very simple for the lecturer to provide on-line documentation,

which can be extended by students.

This is our Twiki server:

https://afnog.iotworkshop.africa/do/view

And this is what you get:

• a serial interface
• I2C
• SPI

On the micro SD card (or a memory stick on one of the USB slots) you can install

a full-blown Linux operating system

(for the Windows gurus: there is also a Windows version)

All you need to have a stand alone computer is

• an HDMI screen
• a USB keyboard and mouse

• in C or C++
• Python
• or any language that Linux supports … and there are many!

keyboard and mouse and use it in stand-alone mode

but we can also make use of the PC resources and access it remotely

There are several ways to access the RPI remotely:

Using the VNC server on the Pi you can access it with a remote desktop from the PC

The secure shell (ssh) allows you to get a remote terminal in the Pi

With scp you can copy files back and forth between the Pi and the PC

With nfs you can mount part of the Pi file system into the PC file system tree

and access the PI SD card as if it was a local PC disk.

connected to the RPI and the keyboard by this computer's keyboard. The connected computer

acts like a graphics terminal for the RPI.

You see on the computer exactly what you would see on a directly connected screen.

The command is:

ssh userOnPi@piIPaddress

Where piIPaddress can be the Pi’s IP address or host name.

If you specify the -X option you can run X-11 based programs where

the X protocol is run over the ssh connection.

For Windows computers you need PuTTY in conjunction with

an X server (e.g. Xming) to connect to the RPi

started an emacs session on the Pi

We use a flat cable and a “cobbler” to bring these signals onto a bread board

where we can build our own electronic circuits for acquisition or control by the Rpi.

Libraries in C/C++, Java and Python are available easing software access to these signals.

a large number of programming languages.

One of the most fashionable languages is Python.

Python is an interpreted language and code can be entered into a Python interpreter

which executes it immediately. Like this, Python can e.g. be used as a calculator.

It is however also possible to write whole programs (scripts) which the interpreter executes

Want to learn Python? Try the Python tutorial!

We will attempt to learn the language in 2 h!

The quit() function exits the interpreter

an Integrated Development Environment (IDE) created specifically for Python instead.

Try idle

The top one contains the editor, the second the Python shell

python scriptName

or we can make it executable and run it like we would run

any compiled C program or any bash script:

However, in Python you do not need to declare the variables.

The interpreter finds the right type by itself.

Here an example:

As you can see, there are no braces around the conditional block but it is indented

# indicates an comment

In addition to the if statement above we have elif and else

Here is the example of a while loop which calculates the Fibonnaci series:

This program uses multiple assignments a,b are assigned in the same line

Again you can see that the block starts with “:” and is indented.

Lists may contain different data types but usually all members of lists have the same type.

Lists have similar properties as strings:

• define sub-lists
• get the length of lists
• concatenate lists

Append, extend, remove, pop, index, count, sort … Have a look at the tutorial for details

The are also further complex data structures which we don’t have the time to go into:

• tuples
• sets
• dictionaries

Using the range function you can create the same type of for loops we know from C.

Keywords like continue and break have the same meaning.

pass does nothing and is used only where a statement is syntactically needed

... and the result:

and call them later in your program

and use these definitions in several main programs.

In our example of the Fibonacci numbers we can save the definitions in a file called fibo.py

In order to use the definitions we must import them with

import fibo

In order to call the functions we have to all the module name:

fibo.fib(20)

or if we we want to import a single function:

from fibo import fib

fib(20)

The module name is found in the variable __name__

... and this is the result:

However it is also possible to include the function calls (the main routine)

into the module e.g. to demonstrate how the functions are to be used.

In this case the name of the module changes to __main__

We can therefore find out if the module is imported or executed by checking the name variable:

if __name__ == "__main__"

this executes the main code only if not imported into a main program

the name of the file to be edited as an argument.

There may also be options that are passed as arguments, e.g.

ls -ls $HOME

These arguments can be read (as strings) in Python:

You may then convert an argument from string to int with

maxFib=int(argv[1])

This code checks if we are running in idle, in which case it asks the user for the arguments.

In case we are called from the command line the arguments are already passed into sys.argv

f = open(‘filename’,’w’)

After which you can write the file. In read mode, the ‘w’ must be replaced by ‘r’

encapsulating data and functions (methods in the oo jargon) that act on these data.

You can create sub-classes having most of the properties of the

base class but provide more data and/or methods or some of the methods are modified (overridden).

This is called inheritance.

Python implements these features.

While in many object oriented languages we distinguish between public and private data,

in Python all data are public.

A convention is to precede a variable name with an ‘_’ if it is not intended for use external to the class.

---+++

f is a method

You may define a method with name __init__which is called when

the instance object of the class is created (in the above example: mc = MyClass ()

The short description of the class can be found in the instance variable _ _doc__

Connection details, calibration parameters etc. can be described in the instance variables

Actions of the sensors like triggering, readout etc. are implemented in methods.

This method allows to

• Initialize instance variables
• Initialize e.g. registers, addresses and the like
• Setup I/O for sensors

The hardware includes:

• a color sensor
• an ultra-sonic distance sensor
• an rgb LED (not strictly necessary)

When a colored paper sheet is placed in front of the senors then this sheet

with the right color will be seen in the virtual world.

The distance of the sheet to the sensors is also reflected in the virtual world.

with its LEDs switched off, in the back

The (white) paper sheet is in frontof the distance sensor

The red ball is the center of the coordinate system