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Python API for the USB-DUX
USB-DUX are open source & hardware data acquisition boxes designed for Linux
https://github.com/glasgowneuro/usbdux
pyusbdux supports the USB-DUX-sigma: 16 analogue inputs (isolated, 24 bit, 1 kHz), 4 analogue out (isolated, 8 bit) and 8 digital I/O
Installation instructions
Make sure that you have all comedi
libraries,
swig
and python3
installed (both runtime and development).
Use your favourite package manager to install the packages.
Then install pyusbdux
by typing::
pip3 install pyusbdux [--user] [--upgrade]
or
./setup install [--user]
Quick start guide
Here are the basic steps how to use the API::
# load the module
import pyusbdux as dux
# create a callback interface
class DataCallback(dux.Callback):
def hasSample(self,sample): # sample arrived
print("s:",sample) # process sample
cb = DataCallback()
# opens the 1st USBDUX device (autodetect)
dux.open()
# Start asynchronous data acquisition in the background: one channel, fs=250Hz
dux.start(cb,1,250)
# do nothing or run a gui
input() # do nothing here
# shutdown
dux.stop()
dux.close()
API documentation
These are the commands which allow you to access the analogue inputs asynchronously
and the analogue outputs, digital input and outputs synchronously::
# opens the comedi device with comediDeviceNumber
open(comediDeviceNumber)
open() # opens 1st USB-DUX device (autodetect)
# Callback interface
class DataCallback(dux.Callback):
def hasSample(self,sample): # sample arrived
# implement your callback handler here
# Starts acquisition of n_channels at the sampling rate of fs.
# Expects an instance of Callback with overloaded hasSample(self,sample).
start(Callback,n_channels, fs)
start(Callback,n_channels) # at fs=250
# gets the actual sampling rate of the running acquisition
getSamplingRate()
# stops the background acquisition
stop()
# writes to a digital pin the value 0 or 1
digital_out(channel, value)
# reads from a digital pin
digital_in(channel)
# writes to an analogue output pin (raw ADC values)
analoge_out(channel, value)
# gets the max raw value of the analogue output
get_analogue_out_max_raw_value()
# closes the comedi device
close()
# returns the name of the board connected
get_board_name()
Any error in comedi throws an exception in python.
Example / demo programs
In the folder https://github.com/berndporr/pyusbdux/tree/master/examples are example
scripts which show you how to sample data from the analogue and digital ports.
Troubleshooting
Spyder
Start your program from the terminal and never within Spyder. Here is
an example::
~/pyusbdux$ cd examples
~/pyusbdux/examples$ python3 ./realtime_plot.py
The problem with Spyder is that it won't let your Python program terminate properly so
that you can examine variables etc. However, this means that
the USB-DUX board keeps running even if it seems that execution has finished.
If you then re-run your program
it won't be able to talk to your USB-DUX.
Bottomline: Use Spyder only for editing, instead run your program from the terminal. Never start
your program from within Spyder.
After an update still the old version is being used
If you use the --user
option to install / update packages Python might keep older versions.
Solution: Do a pip uninstall pyusbdux
multiple times until no version is left
on your computer. Then install it again as described above.