Based on the examples provided by NI for NIDAQmx.h, using the internal clock and "DAQmxRegisterEveryNSamplesEvent" function and some modifications adding FFT fftw3.h libraries to do the FFT of the input signal, everything works fine. The problem I am having is when I want to output the signal gathered from the DAC systems to main. I want to have it as a part of a bigger system so I need the signal in main. Does anyone have experience with this? Find attach the piece of code I am using.