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)