pyFirmata2 1.1.2

Use your Arduino as a data acquisition card under Python

PyFirmata2 turns your Arduino into a data acquisition card which you can directly program with Python.

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.

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

Create an instance of the Arduino class:

from pyfirmata import Arduino
board = Arduino(Arduino.AUTODETECT)

which tries to connect to the first serial port availale on the system.

If this fails you can also specify the port manually:

board = Arduino('COM4')

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].read()

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)

For any other functionality use the pin class.

The pin class

The command get_pin requests the class of a pin by specifying 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()
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.

Credits

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