Can I Output a Finite Waveform with the VirtualBench Function Generator?

Updated Jul 12, 2018

Reported In

Hardware

  • VB-8012

Driver

  • NI-VirtualBench Application and Driver

Issue Details

I am using the VirtualBench Application or API to generate a standard or arbitrary waveform and output said waveform using the VirtualBench function generator (FGEN). The problem is the waveform outputs continuously and I have no options to output a finite waveform. Is this possible? 

Solution

Unfortunately, the function generator only operates continuously. There is not a single-shot/finite generation mode.

Additional Information

It is possible to get single-shot behavior by using the FGEN Start signal as an input for an external circuit.

The FGEN Start signal is generated every time the output buffer completes. Use that pulse to disconnect the FGEN from your device. Detect whether the single-shot has occurred 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 output. 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-flops 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, or use the DC Power Supply if you need more current.

The API has an entry-point for exporting the FGEN Start signal on the TRIG BNC terminal.

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