pymcc provides access to Measurement Computing USB data acquisition
devices, thanks to PyDAQFlex (which
has been copied here so it is not necessary to install it separately).
Note: on Windows, you'll need to install a USB backend like libusb. See the PyUSB README for more information.
This implementation has been verified to work with the USB-1608G, though it
should also work with other MCC USB DAQs. As long as the device supports analog
input, it should just work (TM). Start by installing the package on your
chosen platform. On Windows, that should be all that's needed. On Linux,
you'll need to install a udev rule (e.g. create a file
/etc/udev/rules.d/61-mcc.rules) for your device to be accessible by
non-root users. Populate the file with a line like the following:
SUBSYSTEM=="usb", ATTR{idVendor}=="09db", ATTR{idProduct}=="0110", MODE="0666"
Replace the idProduct attribute with the product ID of your device (the
example above is for the USB-1608G). The product ID can be found using
lsusb. After creating the udev rule, you can log out of your account and
log back in. After adding the rule, you can reload the rules by logging out and
back in or using udevadm. Finally, try running the
examples/check_mccdaq.py script. If no errors occur, the device should be
set up correctly.
pymcc consists of low-level library (PyDAQFlex) as well as a high-level
wrapper called MccDaq. You can create an MccDaq object and then poll
the device for samples.
from pymcc import MccDaq
# sample rate, in Hz
samp_rate = 2048
# number of samples to fetch per `read()` call
samp_per_read = 256
# range of channels to read from, zero-indexed, endpoint inclusive
ch = (0, 3)
# create the device
dev = MccDaq(samp_rate, samp_per_read, channel_range=ch)
# start the DAQ so it begins filling the internal buffer
dev.start()
# request samples from the device
# this method blocks
# it only returns once the requested number of samples have been recorded
dev.read()
# stop the device (call start() again to start over)
dev.stop()The doc strings in <pymcc/mccdaq.py> contain more details about the
parameters and methods of the MccDaq class.
Important Note: the packet size when reading from the device is 512 bytes
when the device is enumerated as a high-speed USB device. This means for
a 16-bit device (like the USB-1608G), you must request a multiple of 256
total samples per read operation. For instance, if you are recording from one
channel (channel_range=(0, 0)), you need to set samples_per_read to
some integer multiple of 256. If you're using two channels, you can read 128
samples at a time (2 channels * 128 samples/read * 2 bytes/sample = 512
bytes/read). See Measurement Computing's Message-based Firmware
Specification for details.