Signal connection between instrument and NI-card

[labviewer]

In fact, I use PCI-6527 card output port to control an instrument switch, the instrument is internally realized by the optocoupler,that is the interface to the instrument is a LED. By controlling the LED, I can control the instrument switch. The instrument manufacturer required 10mA to light the LED of instrument.

My intended signal connection is following:
the instrument LED anode to the PCI-6527 card Dig-; instrument LED cathnode to the PCI-6527 card ground line;
connect the PCI-6527 card 5V to PCI-card Dig+;

Does above electrical circuit work ?
I wonder whether I need to choose external resistor to get the required current or limit too much current to pass LED.

I have another question about a
bove signal connection, when I write 0(logic low) to PCI-6527 card through labview, the switch (in PCI-6527 card) closes, in this case, the instrument LED get the required current and light, so the output signal in instrument is logic High, Does have any signal connection between instrument (that I intended to control) and PCi-6527 card can satified the following requirement: when I write logic low, the output is low, not logic high.

Thanks for help!

[John N]

Hello. Your application sounds really interesting. Your circuit is fine, but you must be *extremely* careful to:
1) put enough resistance in your circuit so that the current drawn from you computer is not too much.
2) be certain that the circuit is connected correctly before turning on the switch since one mistake could short your computer power supply.

The answer to your second question is that you definitely need to make sure there is enough resistance in the circuit for the reasons mentioned above.

I have an idea for your last question, but please read the disclaimer at the end of this message. I am including a small picture that I quickly drew to give you an idea of how to invert the logic of your LED. I must ask you to make all these connections and
calculations yourself.

Good luck!

John N
Applications Engineer
National Instruments


Here is the disclaimer - mostly to make sure you are extra careful when making connections like the ones we are discussing.
For all of these ideas, you must carefully consider whether or not you want to use the board in that way. If you are not sure about the circuits, please have someone verify your system for you. As an applications engineer, I can provide ideas for you, but we are not liable for damage caused by faulty external circuits and connections.