pyFirmata2 1.0.3

Use your Arduino as a data acquisition card

PyFirmata2 turns your Arduino into a data acquisition card which you can directly access from Python without writing any C code.

Just upload the default firmata sketch into your Arduino and you are all set.

pyFirmata2 is an updated version of pyFirmata which adds precise sampling to the API so that it’s possible to filter signals and in general do signal processing. Instead of “sleep” commands which have unreliable timing the Arduino performs the sampling in its firmware and transmits the data then to pyFirmata2. The python application simply registers a callback which is then called after new data has arrived from the Arduino.

Installation

Upload firmata

Upload the standard firmata sketch into your Arduino with File -> Examples -> Firmata -> Standard Firmata.

Install pyfirmata2

The preferred way to install is with pip / pip3. Under Linux:

pip3 install pyfirmata2

and under Windows/Mac type:

pip install pyfirmata2

You can also install from source with:

git clone https://github.com/berndporr/pyFirmata2
cd pyFirmata2

Under Linux type:

python3 setup.py install

Under Windows / Mac:

python setup.py install

Usage

Initialisation

Specify the serial USB port in the constructor of the Arduino class:

from pyfirmata import Arduino
board = Arduino('/dev/ttyACM0')

Under Linux this is usually /dev/ttyACM0. Under Windows it is a COM port, for example COM4. On a MAC it’s /dev/ttys000, /dev/cu.usbmodem14101 or check for the latest addition to /dev/*.

Starting sampling at a given sampling interval

In order to sample analoge data you need to specify a sampling interval in ms. The smallest reliable interval is 10ms.

board.samplingOn(samplinginterval in ms)

Calling samplingOn() without its argument sets the sampling interval to 19ms.

Enabling and reading from an analoge pins

To process the data at the given sampling interval register a callback handler and then enable it:

board.analog[0].register_callback(myCallback)
board.analog[0].enable_reporting()

where myCallback(data) is then called every time after data has been received and is timed by the arduino itself.

You can also read the analoge value of a port any time by issuing a read command:

board.analog[0].enable_reporting()
board.analog[0].read()
0.661440304938

This is useful for reading additional pins within a callback handler to process multiple pins simultaneously. Note that the data obtained by read() is read from an internal buffer which stores the most recent value received from the Arduino.

Writing to a digital port

Digital ports can be written to at any time:

board.digital[13].write(1)

The pin class

If you use a pin more often, it can be worth using the get_pin method of the board. It lets you specify what pin you need by a string, composed of ‘a’ or ‘d’ (depending on wether you need an analog or digital pin), the pin number, and the mode (‘i’ for input, ‘o’ for output, ‘p’ for pwm). All seperated by :. Eg. a:0:i for analog 0 as input or d:3:p for digital pin 3 as pwm.:

>>> analog_0 = board.get_pin('a:0:i')
>>> analog_0.read()
0.661440304938
>>> pin3 = board.get_pin('d:3:p')
>>> pin3.write(0.6)

Example code

The directory https://github.com/berndporr/pyFirmata2/tree/master/examples contains a realtime Oscillsocope with precise sampling rate, a digital port reader, the ubiquitous flashing LED program and a program which prints data using the callback handler.

Board layout

If you want to use a board with a different layout than the standard Arduino or the Arduino Mega (for which there exist the shortcut classes pyfirmata.Arduino and pyfirmata.ArduinoMega), instantiate the Board class with a dictionary as the layout argument. This is the layout dict for the Mega for example:

>>> mega = {
...         'digital' : tuple(x for x in range(54)),
...         'analog' : tuple(x for x in range(16)),
...         'pwm' : tuple(x for x in range(2,14)),
...         'use_ports' : True,
...         'disabled' : (0, 1, 14, 15) # Rx, Tx, Crystal
...         }

Credits

The original pyFirmata has been written by Tino de Bruijn. The realtime sampling / callback has been added by Bernd Porr.