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Lab 5 - Controlling Arduino from the Raspberry pi using Python PyFirmata

Pre requirements

Setting up your Arduino for Firmata

  • On File menu:
    • Select Examples -> Firmata -> StandardFirmata
    • Verify and Upload Standard Firmata code to the Arduino board

Installing pyfirmata

  • Connect via ssh to rapsberry pi
  • Set up your Raspberry Pi with the python firmata libraries. Run the following commands:
> pi@raspberrypi~$ sudo apt-get install python-serial
> pi@raspberrypi~$ sudo pip install pyfirmata

Find arduino port

  • Find out the port name for the USB interface used:
    • Run this command in terminal without Arduino plugged in:
> ls /dev/tty*
  • Plug in the Arduino to the Raspberry Pi with USB cable
  • Run the command again. If a new name appears, then this is the name of your port. Register it to be further used.

Goal 1 - Connecting to an Arduino

  • Create a file 'ex1.py' in ‘/home/pi/lab5’ directory (or open an ipython console)
  • Import the Arduino and util classes from the pyfirmata module and create an object using the USB address you found in the previous step:
>>> from pyfirmata import Arduino, util
>>> board = Arduino('/dev/ttyUSB0') # example

Goal 2 - Blink a LED

  • Use digital pin 13, which is connected to an internal LED.
  • LED on pin 13 should blink for 10 times (time ON = 1s and time OFF = 1s)
  • Close pyFirmata after it is done

Learn the following functions:

    >>> board.digital[pin_nr].write(pin_value) # set the pin values high or low (1 and 0, respectively)
    >>> board.pass_time(t) # Non-blocking time-out for t seconds
    >>> board.exit()

Goal 3 - Controlling analog ports

  • To use analog ports, it is handy to start an iterator thread:
    >>> it = util.Iterator(board)
    >>> it.start()
    >>> board.analog[0].enable_reporting()
  • Reads an analog input on pin A0, and prints the result, repeatedly for 2 minutes (sampling_rate = 10 Hz).

Learn the following functions:

    >>> time.time()
    >>> board.analog[0].read()
  • Save the data received from pin A0 in a file 'data_analog.txt'.
  • The file should have 2 columns:
  • Column 1 - current time (s)
  • Column 2 - pin A0 data (V)

Learn the following functions:

    >>> file = open('data_analog.txt', 'w')
    >>> file.write()
    >>> file.close()
  • Question: What is the maximum sampling rate you can use to acquire the signal?

Goal 4 - Dimming a LED

  • Adapt the code from link 4 about dimming a LED
  • Define a digital pin as PWM
  • The time to reach the max/min of brightness should be 5 s
  • Number of steps to get to the max/min -> use STEPS = 10
  • The LED should be brightening and dimming repeatedly for 2 minutes

Learn the following functions:

    >>> digital_a0 = board.get_pin()
    >>> digital_a0.write()

Links