Is there a way to make the FGEN generate my waveform buffer just once?

[jperch]

Basically, I have a buffer that makes up a pulse. I have been sucessful loading that buffer into the FGEN using LV code. But the FGEN repeats the buffer over and over until I run the stop VI. I want to have the FGEN generate just one pulse until I load the buffer again or provide some other type of signal. I would be happy just running the VI again.  

I tried using a software timer to wait for the pulse to complete and then run the stop VI but that doesn't work. The pulse buffer is only about 10msec long and a simple delay is just not going to cut it. 

thanks,

Joe

[bstreiff]

Nope, sorry. The function generator only operates continuously-- there isn't a one-shot mode.

[jperch]

Well, that is a bummer. But I appreciate the response.

Thanks,

Joe

[JoeFriedchicken]

If you're willing to make a small external circuit, you can get single-shot behavior by using the FGEN Start signal as an input for that circuit.

The FGEN Start signal is generated every time the output buffer completes [1] -- it's like a 'cycle complete' signal. Use that pulse to disconnect the FGEN from your device. Detect whether the single-shot has ocurred using a GPIO line as input to read a state bit on the circuit, and reconnect the FGEN to your device by using another GPIO line as ouput. In summary, this circuit has two inputs and one output:

• (in) FGEN start, to disconnect the FGEN from your device
• (in) GPIO line, to connect the FGEN to your device
• (out) TTL level, to indicate the state of the connection

Parts wise, consider using an analog multiplexer as the switch: input A to the MUX would be the FGEN, and input B would be ground (or some other "safe" level for your device). The rest of the circuit can use logic gates and a flip-flop or two to implement the control logic.

Power wise, you might be able to use the GPIO's 3.3 V source line if your circuit draws less than 20 mA [2], or use the DC Power Supply if you need more current.

The API has an entrypoint for exporting the FGen Start signal on the TRIG BNC terminal [3].

[1] NI-VirtualBench FGEN Help

http://zone.ni.com/reference/en-XX/help/371526A-01/vbhelp/faq_fgen_start_not_happening/

[2] NI-VirtualBench Specifications (page 6)

http://www.ni.com/pdf/manuals/371527d.pdf

[3] Dig Export Signal (VI)

http://zone.ni.com/reference/en-XX/help/374540C-01/lciviref/dig_export_signal/

[jperch]

Joe,

Thank you for that info. I had actually considered investigating something like this. So, thank you for doing that work for me. 🙂

But I think anything like this is probably going to be more work that it is worth.

Thanks again though.

Joe