Getting troubles to send an output from DAQ 6212 to control laser

[Helen12345]

I'm trying to control my laser (PSU-H-LED) with a simple VI (picture 1). My main goal is to control the frequency of my laser within a certain period of time. The vi can successfully run but my laser was not really controlled by it. The laser is linked to PFI12 of NI 6212 (can be detected).

I first tried to generate a pulse output (under counter output) with DAQ (picture 2). The laser was just on all the time after I started to run the vi.   

Then, I tried to generate a digital output instead. I used Dev1/port2/line4 (according to NI 6212 instruction). Again, nothing happened. The laser was just on all the time. I was also thinking to generate an analog out instead but PFI12 port was not in the selection list.

May I have some advice on this? Thank you very much.

[PeterFoerster]

Hi,

it will all come down to what signal your laser needs to receive. From the manual, it seems, that it can either use TTL logic or analog, depending on the switch in the back, so make sure it is set up correctly.

The PFI Lines don't show up for analog connections, as they are digital lines. If you want to use the analog interface, you're going to have to rewire, unfortunately.

Can you check the digital output with a DMM? I don't believe that this is the root cause, but that's what I would check first to make sure the signal gets there. You can also just test with the test panels in the NI MAX, then you don't have to do any programming for now.

What do you expect to happen if you connect a fast digital signal to your laser? From the manual I found I wouldn't expect the laser to do anything but be confused from that signal.

[Kevin_Price]

It's likely that you're generating the pulse and digital toggle signals correctly.  Nevertheless, that's also a fairly easy to thing to test.  An imperfect way is to wire the signal back to an available Digital Input or PFI pin, then run an example that continuously monitors that pin (either digital state or counter edge count).   A better way would be to use an independent measuring device like a scope to check the signal, but I realize sometimes people don't have other equipment available and can only use the board to try to confirm itself.

My suspicion is that things are hardware related -- could be wiring, signal compatibility, or laser configuration.  The instruction manual for it is pretty sparse, have you confirmed proper laser operation under other conditions?  How about with a different, known-good pulse source?  The BNC connector makes me wonder about possible issues due to a low-impedance input for the pulses on the laser power supply.

    When you connect a digital or counter output to a low-impedance sink, you can potentially run into a current sourcing limitation of your board which in turn pulls down the output voltage of your pulse.   If you have a scope, you'd be able to see whether the pulse amplitude changes appreciably depending on whether you're connected to the laser.   

-Kevin P