Can I Trigger DAQmx Read from a RS-232 Signal?

[DanceWiz]

Hi everyone,

I have recently learned how to use Labview to do data acquisition (DAQmx) and have never programatically communicated with a device via RS-232 before... until now that I am learning on the go!  

I have a Uniblitz shutter which has a RS-232 output. Every time the shutter opens and closes, it sends a TTL signal that matches the behavior of the shutter in time.  I also have two photon counting PMTs (i.e. digital outputs) that will be simultaneousely monitoring the behavior of a sample with respect to the shutter's operation (with the PCI 6122).  

I want to see if it is possible to trigger the data acquisition of the PMTs (DAQmx Read), from the signal out of the RS-232, which would be monitoring the behavior of the shutter.  If so, can you please give me some ideas, because I keep going in a circle trying to implement both the DAQmx and the VISA drivers together, so that the DAQmx triggers off of the VISA Read.  I am using Labview 7.1 (and Windows XP).

Thank you very much in advance for any suggestions. 

P.S. Even if I can find a way to correlate the time of the inputs from all signals (the TTL from the RS-232 and the signals from the DAQ board) it would be very helpful.

[JasonSmith]

Are you sure this is a RS-232 connection? You mention that it outputs a TTL signal, which would just be a 5V digital signal, which would be incompatible with RS-232 voltage levels. If you could provide a link to the datasheet for the device we may be able to help interpret it. I looked at a random shutter on their website, and it looked like just a 5V digital output to me, although this was probably not the same shutter you are using.

If this is just a TTL digital line, using a 5V signal, you should be able to just wire it up to one of the available digital trigger lines on your DAQ board, and trigger with it through DAQmx. This triggering will actually be done in hardware and will be far superior to anything you could achieve if you had to receive a signal through the serial port, and then start the acquisition through DAQmx.

-Jason S. 

[Wayne.C]

DanceWiz,

It looks like the Uniblitz shutter control has a RS-232 port and TTL outputs that are intended to be used as external triggers.  I would control the shutter by sending RS-232 commands using the VISA functions in LV.  I would use the TTL output from the shutter control to provide a trigger the data acquisition.