pyusbdux 1.5.8

API for the USB-DUX DAQ boxes for Linux (www.linux-usb-daq.co.uk)

USB-DUX are data acquisition boxes designed for Linux

http://www.linux-usb-daq.co.uk

• 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

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]

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()

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)

# 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()

# 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.