Python Practice

on Raspberry Pi

Created by Ganesh Bhosale in Dwij IT Solutions

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Dwij IT Solutions

From Python to RPi

In Earlier presentation you have learned the basics of python
Now we will go for various uses of python over RPi Hardware and more advanced stuff.

What are we going to learn:

Various Python libraries for Raspberry Pi
Hardware Setups (WiFi, USB)
TKinter (User Interfaces)
GPIO programming
OpenCV (Computer Vision) programming

Python libraries for
Raspberry Pi

Python & Internet

Use of HTTP (Hypertext Transfer Protocol)
We need python-requests library. Lets install.
```
sudo apt-get install python-requests
```
Now open interpreter and import this library


>>> import requests as req
>>> r = req.get("http://google.com")
>>> r.status_code
200
>>> r.text 	# Print data fetched from site

Request Status Codes

Code	Meaning
200	OK
301	Moved Permanently
307	Moved Temporary
401	Unauthorized
404	Not Found
500	Server Error

Weather Data Access

We can use http://openweathermap.org/current
We need web service link:

http://api.openweathermap.org/data/2.5/weather?q=Pune&appid=44db6a862fba0b067b1930da0d769e98

This will give information in JSON (JavaScript Object Notation) Format like below:


{"coord":{"lon":73.86,"lat":18.52},"weather":[{"id":800,"main":"Clear","description":"clear sky","icon":"01n"}],"base":"stations","main":{"temp":291.988,"pressure":950.59,"humidity":52,"temp_min":291.988,"temp_max":291.988,"sea_level":1025.4,"grnd_level":950.59},"wind":{"speed":2.31,"deg":279.501},"clouds":{"all":0},"dt":1457198019,"sys":{"message":0.0101,"country":"IN","sunrise":1457140797,"sunset":1457183515},"id":1259229,"name":"Pune","cod":200}

Program

Temperature in Kelvin; C = K – 273.15


>>> import requests as rq
>>> import json
>>> r = rq.get("http://api.----/weather?q=Pune&appid=1111")
>>> info = json.loads(r.text)
>>> print info['main']['temp']
294.14
>>>

Use this site to understand the json: http://json.parser.online.fr

Hardware Setups

raspi-config

(Raspberry Pi configuration tool)

```
$ sudo raspi-config
```
Detailed information on raspberrypi.org

Enable SSH on RPi

Enter following command in the terminal
```
$ sudo raspi-config
```
Navigate to Advanced Settings -> ssh. Hit Enter
Enable ssh server

Auto mounting Pen-drives

Enable bash commands:
```
sudo bash
```
Install library usbmount using apt-get
```
sudo apt-get install usbmount
```
Check for usb devices
```
df -h
```


root@raspberrypi:/home/pi/practice2/usb# df -h
Filesystem      Size  Used Avail Use% Mounted on
rootfs          7.2G  4.0G  2.9G  58% /
/dev/root       7.2G  4.0G  2.9G  58% /
devtmpfs        180M     0  180M   0% /dev
tmpfs            38M  212K   38M   1% /run
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs            75M     0   75M   0% /run/shm
/dev/mmcblk0p1   56M   19M   38M  34% /boot
root@raspberrypi:/home/pi/practice2/usb# df -h
Filesystem      Size  Used Avail Use% Mounted on
rootfs          7.2G  4.0G  2.9G  58% /
/dev/root       7.2G  4.0G  2.9G  58% /
devtmpfs        180M     0  180M   0% /dev
tmpfs            38M  224K   38M   1% /run
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs            75M     0   75M   0% /run/shm
/dev/mmcblk0p1   56M   19M   38M  34% /boot
/dev/sda1       2.0G     0  2.0G   0% /media/usb0 # Device found

Unmount USB by Commands

Before un-mounting make sure you got correct address
Check devices using df -h


$ sudo umount /dev/sda1

Unmount USB via Python

Before un-mounting make sure you got correct address
Here we need to load module subprocess


>>> from subprocess import call
>>> call(["umount", "/dev/sdb1"])

Start Program at Rpi boot

Here we are going to create new Cron Job
Cron Jobs execute themselves when their time comes up
To edit cron job file
```
$ sudo crontab -e
```
Now put new line into file like below
```
@reboot python /home/pi/MyScript.py &
```
Make sure you don’t create infinite processes here
Note: Only parallel programs without keyboard activity

Start Program at Rpi boot 2

Make system auto-login
```
$ sudo nano /etc/inittab
```
Comment this line
```
#1:2345:respawn:/sbin/getty 115200 tty1
```
Add new line

1:2345:respawn:/bin/login -f pi tty1 /dev/tty1 2>&1

Save File by Ctrl + O and Ctrl + X

Start Program at Rpi boot 2

Run script after auto-login
```
$ sudo nano /etc/profile
```
NoteAdd new line
```
/home/pi/your_script_name.sh
```
Save File by Ctrl + O and Ctrl + X

Create Shell Script to execute program

Inside file your_script_name.sh


#!/bin/bash
sleep 2
sudo python /home/pi/my_program.py

WiFi Setup

Use WiFi Dongle from EDUP. EDUP 802.11n
Plug this dongle in one of USB Port
To check weather wifi device is connected, use command lsusb. This will list all usb devices. Make sure yours is connected.
To check if wifi is detected run ifconfig command

ifconfig


wlan0     Link encap:Ethernet  HWaddr e8:4e:06:0d:c8:17
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:77 errors:0 dropped:8 overruns:0 frame:0
          TX packets:77 errors:0 dropped:3 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:11935 (11.6 KiB)  TX bytes:11935 (11.6 KiB)

No IP Address

Step 1

Run command:
```
$ sudo nano /etc/network/interfaces
```
You will see this:


auto lo

iface lo inet loopback
iface eth0 inet dhcp

Edit this interfaces file to


auto lo

iface lo inet loopback
iface eth0 inet dhcp

auto wlan0
allow-hotplug wlan0
iface wlan0 inet dhcp
wpa-ssid "My_WiFi_Name"
wpa-psk "My_WiFi_Password"

Now Reboot and check ifconfig


wlan0     Link encap:Ethernet  HWaddr e8:4e:06:0d:c8:17
          inet addr:192.168.0.102  Bcast:192.168.0.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:51 errors:0 dropped:2 overruns:0 frame:0
          TX packets:4 errors:0 dropped:1 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:8417 (8.2 KiB)  TX bytes:728 (728.0 B)

The IP means we have successfully connected to Wifi

Date & Time Setup

Raspberry Pi doesn’t have in-built RTC
So it can’t show current time by itself
Either we need to set time after an interval or use Real Time Clock (RTC) Hardware for time
How to Set Time manually:

$ sudo date --set="Sat Aug 16 1:55:16 EDT 2014"

How to check current Date:
```
$ date
```

TKinter (User Interfaces)

TKinter

Only works in LXDE Graphics Environment
Its in-built in Ubuntu, Rasbian & Mac
More information about TKinter on https://wiki.python.org/moin/TkInter

Key & mouse events


from Tkinter import *
root = Tk()

def key(event):
    print "pressed", repr(event.char), " keysym", event.keysym

def callback(event):
    frame.focus_set()
    print "clicked at", event.x, event.y

frame = Frame(root, width=100, height=100)
frame.bind("<Key>", key)		# bind event for key -> key()
frame.bind("<Button-1>", callback)	# bind event for mouse -> callback()
frame.pack()
root.mainloop()

Button & Its Events


from Tkinter import *

def Call():
        lab= Label(root, text = 'You pressed\nthe button')
        lab.pack()
        button['bg'] = 'blue'
        button['fg'] = 'white'
root = Tk()
root.geometry('100x110+350+70')
button = Button(root, text = 'Press me', command = Call)
button.pack()

root.mainloop()

TKinter

More such example on wiki.python.org

GPIO programming

GPIO

(General Purpose Input Output)

Pins provided for external interfacing
Python will let you access the pins by using Module called RPi.GPIO
It comes pre in-built. If not, use following commands with internet connectivity.


$ sudo apt-get install python-rpi.gpio
$ sudo apt-get update

WARNING

Do not short the GPIO Pins of RPi. Short circuit may damage your hardware.
Do not connect LED or any other component directly without resisters in series.

GPIO PINS

Useful Website: http://pinout.xyz

GPIO - HOW TO CONNECT

GPIO outputs are easy; they are on or off, HIGH or LOW, 3v or 0v.

Root Access

Run command:
```
$ sudo su
```

Using GPIO Library


#import library
import RPi.GPIO as GPIO

# set GPIO mode to BCM (Broadcom SOC channel)
GPIO.setmode(GPIO.BCM)

# set GPIO direction as Output
GPIO.setup(25, GPIO.OUT)

# set GPIO pin output as Low
GPIO.output(25, GPIO.LOW)

blink.py


import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)

GPIO.setup(25, GPIO.OUT)

while True:
    GPIO.output(25, GPIO.LOW)
    time.sleep(1)
    GPIO.output(25, GPIO.HIGH)
    time.sleep(1)

button.py

Don’t forget the pull-down resistor, which goes between ground and the input pin


import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)

GPIO.setup(7, GPIO.OUT)
GPIO.setup(8, GPIO.IN)

count = 0

while True:
    val = GPIO.input(8)
    if(val == True):
        count = count + 1
        print("Button pressed.", str(count))
        GPIO.output(7, GPIO.HIGH)
    else:
        GPIO.output(7, GPIO.LOW)
    time.sleep(0.01)

button_sound.py


import pygame.mixer as mx
import RPi.GPIO as GPIO
from time import sleep
from sys import exit

GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)

GPIO.setup(7, GPIO.OUT)
GPIO.setup(8, GPIO.IN)

mx.init(48000, -16, 1, 1024)

sound1 = mx.Sound("/usr/share/sounds/alsa/Front_Center.wav")

soundCh = mx.Channel(1)

while True:
    try:
        if(GPIO.input(8) == True):
            soundCh.play(sound1)
            GPIO.output(7, GPIO.HIGH)
        sleep(0.01)
    except KeyboardInterrupt:
        GPIO.output(7, GPIO.LOW)
        exit()

Enabling sound via Sound Port

Via analog output port
```
$ sudo amixer cset numid=3 1
```
Via HDMI Cable
```
$ sudo amixer cset numid=3 2
```

16×2 LCD interfacing with Raspberry Pi

16×2 LCD interfacing with Raspberry Pi


# Reference: http://dwij.co.in/lcd-interfacing-with-raspberry-pi
# The wiring for the LCD is as follows:
# 1 : GND
# 2 : 5V
# 3 : Contrast (0-5V)*
# 4 : RS (Register Select)
# 5 : R/W (Read Write)       - GROUND THIS PIN
# 6 : Enable or Strobe
# 7 : Data Bit 0             - NOT USED
# 8 : Data Bit 1             - NOT USED
# 9 : Data Bit 2             - NOT USED
# 10: Data Bit 3             - NOT USED
# 11: Data Bit 4
# 12: Data Bit 5
# 13: Data Bit 6
# 14: Data Bit 7
# 15: LCD Backlight +5V**
# 16: LCD Backlight GND

#import
import RPi.GPIO as GPIO
import time

# Define GPIO to LCD mapping
LCD_RS = 7
LCD_E  = 8
LCD_D4 = 25
LCD_D5 = 24
LCD_D6 = 23
LCD_D7 = 18

# Define some device constants
LCD_WIDTH = 16    # Maximum characters per line
LCD_CHR = True
LCD_CMD = False

LCD_LINE_1 = 0x80 # LCD RAM address for the 1st line
LCD_LINE_2 = 0xC0 # LCD RAM address for the 2nd line

# Timing constants
E_PULSE = 0.00005
E_DELAY = 0.00005

def main():
  # Main program block
  GPIO.setwarnings(False)
  GPIO.setmode(GPIO.BCM)       # Use BCM GPIO numbers
  GPIO.setup(LCD_E, GPIO.OUT)  # E
  GPIO.setup(LCD_RS, GPIO.OUT) # RS
  GPIO.setup(LCD_D4, GPIO.OUT) # DB4
  GPIO.setup(LCD_D5, GPIO.OUT) # DB5
  GPIO.setup(LCD_D6, GPIO.OUT) # DB6
  GPIO.setup(LCD_D7, GPIO.OUT) # DB7

  # Initialise display
  lcd_init()

  # Send some test
  lcd_byte(LCD_LINE_1, LCD_CMD)
  lcd_string("Dwij IT Solution")
  lcd_byte(LCD_LINE_2, LCD_CMD)
  lcd_string("Ganesh Bhosale")

  time.sleep(10) # 10 second delay

  # Send some text
  lcd_byte(LCD_LINE_1, LCD_CMD)
  lcd_string("Raspberry Pi in")
  lcd_byte(LCD_LINE_2, LCD_CMD)
  lcd_string("Pune, India")

  time.sleep(10)
  # main function ends

def lcd_init():
  # Initialise display
  lcd_byte(0x33,LCD_CMD)
  lcd_byte(0x32,LCD_CMD)
  lcd_byte(0x28,LCD_CMD)
  lcd_byte(0x0C,LCD_CMD)
  lcd_byte(0x06,LCD_CMD)
  lcd_byte(0x01,LCD_CMD)

def lcd_string(message):
  # Send string to display

  message = message.ljust(LCD_WIDTH," ")

  for i in range(LCD_WIDTH):
    lcd_byte(ord(message[i]),LCD_CHR)

def lcd_byte(bits, mode):
  # Send byte to data pins
  # bits = data
  # mode = True  for character
  #        False for command

  GPIO.output(LCD_RS, mode) # RS

  # High bits
  GPIO.output(LCD_D4, False)
  GPIO.output(LCD_D5, False)
  GPIO.output(LCD_D6, False)
  GPIO.output(LCD_D7, False)
  if bits&0x10==0x10:
    GPIO.output(LCD_D4, True)
  if bits&0x20==0x20:
    GPIO.output(LCD_D5, True)
  if bits&0x40==0x40:
    GPIO.output(LCD_D6, True)
  if bits&0x80==0x80:
    GPIO.output(LCD_D7, True)

  # Toggle 'Enable' pin
  time.sleep(E_DELAY)
  GPIO.output(LCD_E, True)
  time.sleep(E_PULSE)
  GPIO.output(LCD_E, False)
  time.sleep(E_DELAY)

  # Low bits
  GPIO.output(LCD_D4, False)
  GPIO.output(LCD_D5, False)
  GPIO.output(LCD_D6, False)
  GPIO.output(LCD_D7, False)
  if bits&0x01==0x01:
    GPIO.output(LCD_D4, True)
  if bits&0x02==0x02:
    GPIO.output(LCD_D5, True)
  if bits&0x04==0x04:
    GPIO.output(LCD_D6, True)
  if bits&0x08==0x08:
    GPIO.output(LCD_D7, True)

  # Toggle 'Enable' pin
  time.sleep(E_DELAY)
  GPIO.output(LCD_E, True)
  time.sleep(E_PULSE)
  GPIO.output(LCD_E, False)
  time.sleep(E_DELAY)

if __name__ == '__main__':
  main()

OpenCV (Computer Vision) Programming using Python

References

Thank you

- Ganesh Bhosale
- Dwij IT Solutions

Did you liked this tutorial ?

Checkout more such tutorials on: http://dwij.net/tuts

Python Practice

on Raspberry Pi

Your support

From Python to RPi

What are we going to learn:

Python libraries forRaspberry Pi

Python & Internet

Request Status Codes

Weather Data Access

Program

Hardware Setups

raspi-config

(Raspberry Pi configuration tool)

Enable SSH on RPi

Auto mounting Pen-drives

Unmount USB by Commands

Unmount USB via Python

Start Program at Rpi boot

Start Program at Rpi boot 2

Start Program at Rpi boot 2

Create Shell Script to execute program

WiFi Setup

ifconfig

Step 1

Date & Time Setup

TKinter (User Interfaces)

TKinter

Key & mouse events

Button & Its Events

TKinter

GPIO programming

GPIO

(General Purpose Input Output)

WARNING

GPIO PINS

GPIO - HOW TO CONNECT

Root Access

Using GPIO Library

blink.py

button.py

button_sound.py

Enabling sound via Sound Port

16×2 LCD interfacing with Raspberry Pi

16×2 LCD interfacing with Raspberry Pi

OpenCV (Computer Vision) Programming using Python

References

Thank you

Python libraries for
Raspberry Pi