Run Vi using TTL input from external source

Hello guys

I am currently making a PIV system but I need the VI to run according to an external TTL signal.

I need my program to fire an LED for a number of pulses during the high time of the input TTL and not to fire during the low time of the input TTL. I am using an arudino to provide the input TTL.

My code is attached.

Thanks in Advance