2010910 pi workshop notes

Intro

Raspberry Pi 3 computer
OS (Raspbian) loaded on SD card
All GPIO pins are flexible 3.3V OUT or IN (will generate floating voltage when not programmed)
GPIO can be programmed using gpio utility: http://wiring.com/the-gpio-utility/
UART pins carry data (RX=receive, TX=transmit), allows connection of devices (GPS), 3V->3V, GND->GDN, RX->TX, TX->RX
Sends text signals, each character encoded in 8bits ("packed" encapsulated into a "start bit" and a "stop bit")
Speed is 9600 Baud (1 Baud = 1 bit per sec)
To access this data, you can either use a Python script, or a software called "screen"
directory "/dev/ttyACM0 9600" contains a new file that represents the connexion to a device (arduino, printer, etc.)
I2C protocol
For example: BMP280 sensor temperature and pressure sensor (4pins=3V, GND, SDA, SCL)
On pi, up to 127 sensors can be connected to the SDA and SCL ports. Each device has a fix-programmed specific address.
i2c-tools is a program that allows to detect from all these sensors using the i2cdetect protocol.
"sudo raspi-config" to configure the pi computer
Step 1. Tell pin to be GPIO2
Step 2. Tell pin to be ON or OFF
2 ways of accessing the pins: GPIO# or pin#
"GPIO-g" flags to GPIO#

First test

If we want to connect the LED on the GPIO4 port:

Controlling GPIO ports using Python:

Or using BASH (Shell) command line (UNIX language):

sudo -i 

echo "4" > /sys/class/gpio/export 

echo "out" > /sys/class/gpio/gpio4/direction 

echo "1" > /sys/class/gpio/gpio4/value <-turns it on 

echo "0" > /sys/class/gpio/gpio4/value <-turns it off 

Or GPIO utility command:

gpio -g mode 4 out 

gpio -g write 4 1 <-turns it on 

gpio -g write 4 0  <-turns it off 

The Operating System

An OS is a piece of software that people wrote to use a computer in an easy and structured way.
Linus is the kernel (not an operating system), robust, versatile, stable.
Operating system is Raspian in our case.

Linux always has a BASH (Shell) terminal: type something, press enter, view output.

The terminal uses: arrows
enter key (execute)
tab key (autocomplete)

Everything in Linux is either a FILE or a DIRECTORY

man

stands for manual and gives instructions on how to use commands, eg. "man cat"

pwd

shows the directory we're in

ls

lists all items in this directory

ls -ailh

give the size of all files in the directory

rm -r NAME

remove directory

rm NAME

remove file

mv FILENAME ..

moves file NAME into the upper directory

mv FILENAME DIRECTORY

moves FILENAME into any DIRECTORY

ctrl c

cancels all commands

ctrl l

cleans the screen

sudo -s

login as root

exit

leaves root mode

cat [FILE NAME] | less

-> the pipe character "|" will take the output of one command into the next command

Bash scripting

test1:

nano myfirstscript.txt

#! /bin/bash"
echo Hello!
echo World!
whoami

chmod +x myfirstscript.txt

->makes the file executable -> into some program that you can run

./myfirstscript.txt

-> executes the file

test2:

nano mysecondscript.txt

--

#! /bin/bash
echo Hello!
echo World!
whoami

mkdir woz
touch woz/niak.txt

--

chmod +x mysecondscript.txt

./mysecondscript.txt

LEDBlink

#! /bin/bash

tells the terminal the langage of code (Bash here)

while true; do
gpio -g write 4 1
sleep 0.5
gpio -g write 4 0
sleep 0.1
done

Makes pin 4 (here a LED) blink forever (while)

Networking

to find IP address of Raspberry Pi:

hostname -I

will retrieve the IP address

ssh pi@... (IP address)

1. find a screen with HDMI cable
2. plug into Raspberry Pi
3. plug mouse in the USB
4. use the graphical user interface on the screen

top right corner, wifi signal, select the wifi network, type in password, write down IP address, then can be used to connect