Imaq 1428 external trigger TTL signal

[davie]

Hi,

I have an IMAQ 1428 card but am having problems with the external triggers.  I use the Imaq generate pulse.VI to trigger a laser.  The laser itself works fine.  However, when I run my program the laser does not fire.  When measuring the voltage output on the external trigger, the high voltage is 4.8V but the low voltage is 2.4V on the external trigger.

I also tried LL Triger Drive.vi and tested it on asserted and unasserted.  Unasserted yields 2.4V and Asserted yield 4.8V

I realize that the low voltage for a TTL signal should be closer to 0-0.4V.  What could be causing the low voltage to be so high?

I have both labview 7.1 and labview 8 installed.  It does the samge thing in both versions.  The program was originally written in labview 7.1

Thanks,

David

[GiGe]

Hi David,

Do you see this behavior when there isn’t anything connected to your system?  You may want to measure the output when there isn’t anything connected to it to see if you still get the same readings.  Also try running the example in labview called LL Pulse Generation.  (Help»Find Examples»Hardware Input and Output»IMAQ»Signal Input and Output»LL Pulse Generation).  Do you see the same behavior when running that example?  Let me know how that goes.

Have a great day,

GG

[davie]

Yes, when there's nothing connected the low voltage reading is 2.4V and high voltage is 4.8 when running imaq generate pulse.vi  The behaviour doesn't change with or without the laser connected.

I tried LL pulse generation.vi  When starting the program the voltage is 4.8V.  Once the generate pulse3.vi is called it drops to 3.4V.  Afterwards when the while loop is executing the voltage on the external signal fluctuates from 3.3V-4.4.V approximately.  Once the LL pulse generation.vi is stopped, it returns back to 4.8V.  This was with nothing connected also.  When the laser was connected, it behaved in the same manner.

This was done with labview 7.1 with NI-IMAQ 3.7 drivers

I've attached the two VIs I've been using.

My guess is that when a TTL signal is sent from the external trigger, the low voltage is not low enough since it really should be at 0.4V and not 2.4V

I don't know whether this is a problem with the card or the Labview software/IMAQ drivers.  If it is a hardware problem whether it can be compensated for through modification of a subVI or adding some external circuit.

[GiGe]

Hi David,

One other thing that we should check is to see if you are seeing this same behavior on all of the trigger lines.  It could be that there is just a problem with one of the lines.  There really isn’t anything in your program that would cause that behavior.  Is everything else functioning properly on the card?  Are you to run Snap or Grab examples?  It will help to know if it is just the trigger lines that aren’t functioning properly or if other functionality is also malfunctioning.  Let me know how that goes.

GG

[davie]

I'm using grab but for high speed image capturing.  I don't need to take video.  The same behaviour occurs on all trigger lines (except one which I don't use since I know it doesn't work, it always reads 0.22V).  The camera that is attached works fine.  It's just the trigger lines.

I tried switching the Imaq card to a different PCI slot but got the same behavior again.

[changle0204]

a silly question ,where is the external trigger , the CC1 in the camera link or  one line in the triggers

[Justin__D]

Hi Changle0204,

I'm not sure if I completely understand your question.  The IMAQ boards can used with many different triggers.  This link explains this a little more.

KnowledgeBase: IMAQ Boards That Support Routing to the Camera Control Lines

[dirtpics]

I'm having same problem with the 1428 card I'm using.  As soon as the computer is turmed on, voltage is sent to the trigger line I'm using from the trigger connector on the bottom of the  card.  After I run the trigger/image acquisition loop the voltage drops and then goes back to high, creating an inverted pulse on the oscilliscope.  I'd much rather have the the voltage go from zero to high and back to zero again so that I don't get an extra trigger every time I start or shut-down the computer.

If anyone has been able to figure out a solution for this and is willing to share their knowledge, I would be very thankful.

[Z'atari]

What version of iMAQ are you using?

[dirtpics]

I think it is 3.7 that I am using now.  I know it's not the most current version anyway.