Pseudo Random Binary Sequence Output from myRIO

[mcbriley92]

Hello,

I'm attempting to run a near-field communication experiment and need to generate a pseudo random binary sequence on a digital output pin of the myRIO.

I've looked at the PRBS express VI but can't seem to figure out how to control the sampling frequency.

I need to generate the signal at a switching frequency between 100K-200K Hertz.

Can anyone help explain how to control the frequency of the PRBS express VI?

Thanks,

Matt

[Dennis_Knutson]

If I recall correctly, you don't set the sampling frequency of the prbs signal. You set the sampling frequency of the hardware.

[mcbriley92]

Care to elaborate?

[Dennis_Knutson]

I haven't used the myrio but there should be a way to set the output rate. When I generated a prbs signal with a standard DAQ card, I used a timing function of DAQmx to output the ones and zeroes that were in the array.

[mcbriley]

So I found a really simple way of generating a PRBS and outputing it on the digial output pins. I've attached a snapshot of the block diagram to do this.

However, the highest switching frequency I've been able to obtain through this method is 22.727 kHz.

I need to reach between 100k-200kHz.

Any suggestions on alternative methods or ways to improve this method?

Thanks,

Matt

[Bob_Schor]

I suspect the problem is that you are sending single points (as opposed to a PRBS, where S stands for "Sequence", i.e. a train of pseudo-random binary numbers) to the Express VI.  You are probably seeing the overhead of trying to output "one point at a time", where the hardware wants to output at a much faster clock rate (on the order of 100KHz or better).

BS