Instrument Control (GPIB, Serial, VISA, IVI)

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NI-VIA to Send Digital Triggers?

Hi everyone,

I have a question regarding the capabilities of NI-VISA, but first I would like to give you an overview of what the end goal is.  


I work in a Biomedical Engineering lab, and we do a lot of work with EEG.  We currently are using an EEG amplifier system which has dedicated digitial input lines.  These I/O lines are accessible through a 10 pin plug (8 inputs + digital ground + Vcc) on the back of the amp.  The included cable to access these lines is the 10-pin connector on one end and a DB25 connector on the other.  Unfortunately, the PCs we are using do not have a DB25 port, so we bought this DB25 to USB adapter in hopes of being able to configure it to interface with LabVIEW in sending digital lines.


When I plug the device into the computer and open device manager, I see it listed under the "Universal Serial Bus Controller" as "USB Printer Support".  I followed the guidelines found in the USB Instrument Control Tutorial to create a driver for the device, and can now see it in MAX and VISAIC.  


After researching how to send data (ideally TTL triggers) through the NI-VISA, the only thing I am finding is how to send hexidecimal information through VISA.


Therefore, I have three main questions:

1. Is it possible to send TTL triggers through NI VISA?

2. Do I need a device that is assigned a COM port on the PC?

3. Is it possible to reconfigure my "USB printer service" device to be assigned a COM port?


I've never done any kind of device/serial interfacing, so a little help from someone with some expertise would be greatly appreciated!

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Message 1 of 8

1) It is possible for 8 lines

2) I would choose another device also on usb that is much easier to interface.


I mean a 6501 digital io device from NI.

it is very easy to do this with LabVIEW.


the other posibility is indeed sending bits (characters) to the parallel port.

that is not a .com device but could be the LPT port in your system.


Good luck

greetings from the Netherlands
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Message 2 of 8

Thanks Albert.

The 6501 wouldn't really be ideal because the EEG amp has to be connected through the DB25.  We already have several DAQs (6009, 6210, etc), and really could use them to acoomplish the goal. We would just have to buy a DB25 to 8 x BNC cable from the EEG amp company (for a pretty penny I'm sure) and connect digital outputs of a DAQ to the BNC connectors.  Since the cable is relatively expensive compared to the $5 USB adapter we got, we wanted to explore that option.  


When you say Parallel port, do you mean my NI VISA device? Could you ellaborate on LPT and sending bits through it? This is all new to me.

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Message 3 of 8

@dmhuffman2010 wrote:

The 6501 wouldn't really be ideal because the EEG amp has to be connected through the DB25...Since the cable is relatively expensive compared to the $5 USB adapter we got, we wanted to explore that option.

Be very careful here.  Just because there is a DB25 connector does not mean that the signals are matched up.  Assuming you bought a USB to parallel port adapter, you should probably at least read up on parallel ports on wikipedia.

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Message 4 of 8

I would use a self soldered cable anyway.

Are you sure that the db25 connector is corect for the instrument?

Db25 is used in a lot of devices without the parallel port pinout.


when I speak about parallel port I indead mean the visa parallel port.

it is probably named lpt10.


In visa parallel and serial ports use the same software layer although the hardware is really different.


greetings from the Netherlands
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Message 5 of 8

I was under the assumption that I could write a program that would send data through the correct pins of the DB25 adapter, but maybe that isn't possible.  In MAX, I do see an LPT listed, but I believe its the on board parralel port on my current PC (the end use laptop does not have a physical parralel port).  The adapter I have configured shows up in MAX as a "USB RAW Resource".  Would I be able to assign LPT to it by entering something like "LPT2" as the VISA alias?

Here is a screenshot of MAX and the VISAIC if that helps.

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Message 6 of 8

Actually, I was mistaken. My PC doesn't have a parallel port on the back. Just display connections as far as I can tell... could the LPT1 be from NI VISA? It seems unlikely, as it does not disappear when I disconnect the device.  I can't seem to find anything listed as "LPT1" in device manager either. Sorry I'm ignorant to a lot of this... this is my first go with parralel interfacing.

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Message 7 of 8

Sure don't use the VISA-raw. You need more expertise than I have for using that. 

Normally there should be a driver, maybe on the web, that changes your usb device into a real parallel port.

You should also check your windows devices if a parallel port is available.


I still advise you to use the 6009 or 6501 for the digital IO. on the side of the USB6509 you can screw the wires and the only soldering you need is on the other side. Somebody in the lab should be able to help you there.

greetings from the Netherlands
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Message 8 of 8