Using Labview to control the Digital I/O of a Virtual Bench

[md12g12]

Hi,

I am trying to use this example to create a 5V pulse to a device. http://www.ni.com/example/52071/en/. I want to use the 5V digital output line on a Virtual Bench to create a short laser pulse. (The laser is just driven by a 5V pulse of any length.) I can use it to output 5V manually (just by toggling the button), but I dont know how to incorporate the Output Array Control into a timed loop or something else. 

Thanks,

Matthew 

[crossrulz]

How fast of pulses do you need?  And how accurate are these pulse widths?

I do not think the VirtualBench DIO can be used for pulsed outputs since they are software timed.  You might be able to do something with the Arbitrary Waveform Generator though.

[md12g12]

I am not yet sure how fast, but down to a millisecond would be very nice. And I would use the FGEN but that is being used to generate pulses down to 1us for a different part of the experiment sadly. The pulses dont need to be accurate as such, just reliable. If I can set it to 15ms and always get a 17ms pulse then that is fine, I can calibrate for that, but if the pulses vary much with the same settings then that would be a problem. 

However even if they are not stable I would like to be able to pulse it at the ~100ms range. Does that help answer your question?

[crossrulz]

100ms might be doable mostly reliable, but on a Windows machine you cannot rely on software timing.  What you really should do is get a simple DAQ that has a counter output that is capable of outputting pulses (double check in the data sheet).  Then you can use simple DAQmx functions to tell the hardware to output a pulse.  With the hardware controlling the timing, you will get a lot more consistent pulses.

[md12g12]

Ok thanks, but in the meantime how would I get this working as intended? I have attached the VI im using. It can turn the laser on with the pulse button, but then not off. I am very new to labview so I think its a basic mistake.

Thanks in advance

[JoeFriedchicken]

Hi Matthew,

I believe you can do what you need with VirtualBench, but it's a little outside the designed behavior of the hardware.

md12g12 wrote:

I want to use the 5V digital output line on a Virtual Bench to create a short laser pulse. (The laser is just driven by a 5V pulse of any length.) I can use it to output 5V manually (just by toggling the button), but I dont know how to incorporate the Output Array Control into a timed loop or something else.

crossrulz wrote:

I do not think the VirtualBench DIO can be used for pulsed outputs since they are software timed.

This is correct -- the VirtualBench GPIO instrument API is 100% software timed -- as fast as the program can write to the device is as fast as you can go. However, the GPIO also has another mode: SPI, which is hardware-timed.

md12g12 wrote:

The pulses dont need to be accurate as such, just reliable. If I can set it to 15ms and always get a 17ms pulse then that is fine, I can calibrate for that, but if the pulses vary much with the same settings then that would be a problem.

Try this example and use the scope to measure the SPI Clock's period (dig/0). If that is too fast, you can write a different digital pattern and measure the MOSI Signal's period (dig/1).

VirtualBench: Master SPI With the DIO

http://www.ni.com/example/52585/en/

VirtualBench Digital I/O Pinout and Connections

http://zone.ni.com/reference/en-XX/help/371526B-01/vbhelp/diopinout/

[md12g12]

The speed is ok, for now I would be happy with any pulse at all really. I just need help with making labview output a pulse of true to the boolean array. Something along the lines of the VI I attached would be great, but I dont know how to use a timer to change a boolean value.