API for the USB-DUX DAQ boxes for Linux (www.linux-usb-daq.co.uk)
USB-DUX are data acquisition boxes designed for Linux
- USB-DUX-D: 8 analogue inputs (isolated, 12 bit, 1 kHz), 4 analogue out (isolated, 12 bit) and 8 digital I/O
- USB-DUX-sigma: 16 analogue inputs (isolated, 24 bit, 1 kHz), 4 analogue out (isolated, 8 bit) and 8 digital I/O
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]
Quick start guide
Here are the basic steps how to use the API:
# load the module import pyusbdux as dux # opens the 1st USBDUX device (autodetect) dux.open() # Start asynchronous data acquisition in the background: one channel, fs=250Hz dux.start(1,250) # Now we read data at our convenience in a loop or timer or thread # The following lines need to be repeated # Let's check if samples are available if (dux.hasSampleAvailable() == 0): # nope! Do something else or nothing # Let's get a sample (array of all USB-DUX channels) sample = dux.getSampleFromBuffer() # do something with the sample, for example print it print(sample) # rinse and repeat! # end of loop # shutdown dux.stop() dux.close()
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) # Starts acquisition of n_channels at the sampling rate of fs. start(n_channels, fs) start(n_channels) # at fs=250 # Checks if samples are available (=1) or zero if not. hasSampleAvailable(); # Returns one sample from all channels. # returns always 16 values irrespective of how many channels # are measured. Blocking call if no samples are available. getSampleFromBuffer() # 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.
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.
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