Raspberry PI controlling an Arduino via the pyfirmata protocol

The Raspberry PI is good for a lot of things from computer clusters to home automation but its missing a few things such as a real time clock, terminal/barrel power connector, or  Analog pins.  The Arduino has analog pins that can be read by the USB virtual serial port from the Raspberry PI.

In MagPI issue 7, has a great article on using the firmata protocol to communicate between   Arduino and the Raspberry PI.

Requirements

• A raspberry PI
• A Arduino
• USB Cable A to B
• pyFirmata python library (documentation)

Install and setup 

1. Enable SSH on the Raspberry PI
2. Install Adafruit Learning System Raspberry Pi WebIDE
3. Get the required packages:

   sudo apt-get install python-serial mercurial

4. Install pyFirmata

   sudo apt-get install python-serial mercurial
   hg clone https://bitbucket.org/tino/pyfirmata
   cd pyfirmata
   sudo python setup.py install
   cd .. ; sudo rm -r pyfirmata

Source code 

Read analog pin 1

import pyfirmata

# Create a new board, specifying serial port
board = pyfirmata.Arduino('/dev/ttyACM0')

# start an iterator thread so that serial buffer doesn't overflow
it = pyfirmata.util.Iterator(board)
it.start()

# set up pins
pin0=board.get_pin('a:0:i')             # A0 Input      (LM35)
pin3=board.get_pin('d:3:p')             # D3 PWM Output (LED)

# IMPORTANT! discard first reads until A0 gets something valid
while pin0.read() is None:
    pass

while True : 
  print "PWM: " + str( pin0.read() ) 
	board.pass_time(1)                  # pause 1 second

board.exit()