Slides from my talk about Python and Raspberry Pi in Pycon

1. Python in Raspberry Pi
Sudar Muthu (@sudarmuthu)
http://github.com/sudar
http://hardwarefun.com

2. I love Python ;)

3. Credit Card Sized
Computer

4. Basic Electronics
http://en.wikipedia.org/wiki/File:OhmsLaw.svg

5. GPIO Pins
http://learn.adafruit.com/assets/3052

6. Setup Python
sudo apt-get install python-dev
sudo apt-get install python-rpi.gpio

7. Set the status of GPIO Pins
https://github.com/sudar/raspberry-pi-sketches/blob/master/led-blink/led-blink.py

8. Set the status of GPIO Pins
import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BOARD)
GPIO.setup(12, GPIO.OUT)
try:
while True:
GPIO.output(12, GPIO.HIGH)
time.sleep(1)
GPIO.output(12, GPIO.LOW)
time.sleep(1)
finally:
GPIO.cleanup()
https://github.com/sudar/raspberry-pi-sketches/blob/master/led-blink/led-blink.py

9. Demo
Let there be Light
https://github.com/sudar/raspberry-pi-sketches/blob/master/led-blink/led-blink.py

10. Changing the brightness of the LED
import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BOARD)
GPIO.setup(12, GPIO.OUT)
p = GPIO.PWM(12, 50) # channel=12 frequency=50Hz
p.start(0)
try:
while True:
for dc in range(0, 101, 5):
p.ChangeDutyCycle(dc)
time.sleep(0.1)
for dc in range(100, -1, -5):
p.ChangeDutyCycle(dc)
time.sleep(0.1)
finally:
p.stop()
GPIO.cleanup()
https://github.com/sudar/raspberry-pi-sketches/blob/master/led-blink/pwm.py

11. Demo
Can you see the brightness changing?
https://github.com/sudar/raspberry-pi-sketches/blob/master/led-blink/pwm.py

12. Reading the status of the Pin
import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BOARD)
GPIO.setup(11, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
try:
while True:
if GPIO.input(11):
print "Button is on"
else:
print "Button is off"
time.sleep(0.1)
finally:
GPIO.cleanup()
https://github.com/sudar/raspberry-pi-sketches/blob/master/button-input/button-input.py

13. Reading the status of the Pin
https://github.com/sudar/raspberry-pi-sketches/blob/master/button-input/button-input.py

14. Demo
What happens when the button is pressed?
https://github.com/sudar/raspberry-pi-sketches/blob/master/button-input/button-input.py

15. Combining Input and Output
import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BOARD)
GPIO.setup(11, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
GPIO.setup(12, GPIO.OUT)
try:
while True:
if GPIO.input(11):
print "Button is on"
GPIO.output(12, 1)
else:
GPIO.output(12, 0)
time.sleep(0.1)
finally:
GPIO.cleanup()
https://github.com/sudar/raspberry-pi-sketches/blob/master/button-and-led/button-and-led.py

16. Combining Input and Output
https://github.com/sudar/raspberry-pi-sketches/blob/master/button-and-led/button-and-led.py

17. Demo
Let’s control the LED by pressing the button
https://github.com/sudar/raspberry-pi-sketches/blob/master/button-and-led/button-and-led.py

18. What more can be done?

19. More protocols
• I2C
• SPI
• Serial

20. Interacting with webcam
• “PyGame” provides easy interface
• Can get fancy using “opencv”
• Both USB and GPIO interface are supported

21. Distributed Computing
• Each Pi can be used as cheap node
• Form grids using a cluster of Pi’s
• Can share CPU, memory and disk space
http://www.cl.cam.ac.uk/projects/raspberrypi/t
utorials/distributed-computing/

22. Limitations
• No built-in Analog to Digital support
• Can’t run Inductive load (motors)
• Is not real-time (CPU might be busy)
• No “safe circuits” present
• Operates at 3.3V and is not directly
compatible with Arduino voltage

23. Best of two worlds
http://learn.adafruit.com/assets/3199 http://learn.adafruit.com/assets/2123

24. Links
• Source code -
https://github.com/sudar/raspberry-pi-sketches/
• My blog - http://hardwarefun.com
• Python GPIO -
https://code.google.com/p/raspberry-gpio-
python/
• Distributed computing using Pi -
http://www.cl.cam.ac.uk/projects/raspberrypi/tu
torials/distributed-computing/

25. Thank you
Sudar Muthu
http://hardwarefun.com