IMPORTANT: The Open Ephys GUI documentation has migrated to a new site – please visit https://open-ephys.github.io for the most up-to-date information.

This source module makes it possible to stream analog and digital data from National Instruments hardware. The module can acquire data from multiple PXI-based and/or USB-based National Instruments (NI) devices simultaneously. The NIDAQmx module can also be used in tandem with the Neuropix-PXI plugin, to read in analog and digital inputs in parallel with Neuropixels data. 

For information on how to install the Neuropixels version of the Open Ephys GUI, please see this page.

Note: 

Hardware requirements

For PXI-based acquisition: 

• One PXI chassis (so far we've tested National Instruments PXIe-1071 and PXIe-1082)
• One PXI remote control module, housed in the PXI chassis (we've tested National Instruments PXIe-8381 and PXIe-8398) – requires NIDAQmx driver 19.0 or higher
• One PXI-based analog and digital I/O module (we've tested and highly recommend National Instruments PXI-6133)
• Cables to connect the remote control module to the PCIe card (e.g., National Instruments MXI-Express Cables, Gen 3 x8)
• One PXI-based NI-DAQ BNC/terminal block (we've tested the BNC-2090A and BNC-2110)

For USB-based acquisition:

• One NI USB device (we've tested the USB-6001)
  • These devices are known to experience 'signal ghosting' if unused analog input channels are not grounded. Grounding at least one positive terminal of an unused analog input channel can reduce ghosting by ~99% of the highest amplitude active channel. 
  • Many NI USB devices do not contain internal clocks, and as a result, the analog and digital input channels cannot be synced via hardware like many PXI devices. We see digital inputs leading analog inputs by ~10ms with a USB-6001 on the hardware setup described below. We are currently working on a software buffering solution that will better synchronize analog and digital input signals on USB devices. 
• One micro-USB (or related) cable to connect the USB device to the computer. 

Important Note: The NIDAQmx plugin is currently only able to sync analog and digital input signals from NI cards that support correlated (hardware-timed) digital I/O. It is not trivial to discern this capability from the NI data sheets, so please double-check that your particular card supports this feature prior to purchasing a card. Again, we highly recommend the PXI-6133 card. This module also does not yet support NI cards that only have digital inputs (ex: NI 6521). 

If you've tested the GUI with NI devices not listed above, please let us know!

Minimum computer specifications

So far, this module has been tested on a computer with the following hardware:

• Intel Core i7-6700 CPU @3.40 GHz 
• 16 GB RAM
• Samsung SSD 860 EVO 1TB 
• Intel HD Graphics 530
• Windows 10 operating system

It's highly likely that other types of machines will be fine as well, so please get in touch once you've tested them!

Note: We have successfully been able to record data from 1 NI PXI-based device (8 AI + 8 DI) @ 30kHz + 1 NI USB-based device (8 AI + 13 DI) @ 2.5kHz + 2 Neuropixels probes simultaneously. Adding additional devices/channels will bog down the GUI's recording system, which we are currently overhauling to support 8+ Neuropixels probes. 

Connecting to the NIDAQmx system

Once your PXI system is up and running, you can drag and drop the NIDAQmx module from the Processor List onto the Editor Viewport. The module automatically checks for all connected NI devices and by default loads the first device found. The device product name appears directly to the right of 'NIDAQmx' in the title.

If multiple NI devices are found, a 'Device Swap' button will appear in the top right corner that acts as a toggle switch to cycle through all available devices. The module only looks for devices when the plugin is dropped into the EditorViewport. If a new device is connected after the plugin is dropped, you will need to drop a new NIDAQmx module to be able to connect to the new device.

The editor will automatically generate control buttons for each analog and digital input available on the currently selected NI device. Each analog channel contains a channel status toggle button as well as a terminal configuration toggle button. The channel status toggle button is set to on (green) by default for all channels and is intended to enable/disable channels on the fly. Toggling an enabled channel to off (gray) will 'zero-out' the data coming in on that channel. 

Each analog channel also contains a terminal configuration toggle specific to the device connected. Possible terminal device configurations are RSE (Referenced Single-Ended), NRSE (Non-Referenced Single-Ended), DIFF (Differential) and PDIF (Pseudo-Differential). The terminal configuration toggle setting in the module should match the configuration in your experimental setup. Since most NI devices cannot infer the terminal configuration electronically, it is on the user to ensure the module configuration matches the experimental setup prior to acquiring and recording data. An inconsistent terminal configuration can affect the amplitude and voltage offset of the incoming data.

Each digital channel contains a channel status toggle button as well. Disabling digital channels is particularly useful when a digital input line is constantly high or a digital line is not used at all. 

On the right side of the module are pull-down selection menus to select the sample rate and voltage range of all analog input channels (set individually for each channel). The module defaults to the highest sample rate as well as the largest voltage range available on the devices. Sample rate and voltage range selection are both disabled during data acquisition and recording. 

Synchronizing with other data streams

The NIDAQmx module has its own sample clock, even if it's in the same PXI chassis as other hardware (e.g. a Neuropixels basestation). Therefore, it needs to be treated as a separate device when performing offline synchronization.

To align timestamps across devices, one device has to be treated as the "master" clock, and all other sets of timestamps must be scaled and shifted to match this clock. This requires that a digital sync line is shared across all devices. For now, you'll need to manually connect a sync line to one of the digital input lines on all of your devices. If you don't already have a solution for this, we recommend using an Arduino running the sync-barcodes program, which generates unique temporal barcode patterns every 30 s. This will allow you to align sample clocks accurately, even if your devices are stopped and started at different times.

To perform the alignment, you'll need to identify the first and last shared sync pulse in the recording. The temporal offset between the start of the first sync pulses defines the shift between any device and the master clock. Once you know this, you can calculate the expected interval between the firs and last sync pulse (given the expected sample rate of a device). The ratio of the actual interval to the expected interval defines the scaling factor for that device.

Then, each non-master clock can be transformed by the following equation (in Matlab):

aligned_timestamps = scaling .* original_timestamps + shift;

The "aligned_timestamps" will now be aligned to the master clock, and are ready for analysis.