Hi Gaby,
You can use the digital output of your board to produce the required TTL signal. As mentioned by Dr. Imad, the LabVIEW examples are good starting points. You can find them by going to the "Example Finder" of the Help menu. In the "Browse" tab, Hardware Input and Output >> DAQmx >> Digital Geneartion >> Write Dig Channel.vi
(If you're using the Traditional DAQ driver, go to Hardware Input and Output >> Traditional DAQ >> Digital Input and Output>> E-Series >> Write 1 Pt to Dig Line.vi
Cheers,
Lesley Y.