How do I limit the duty cycle of a recovered signal?

[EdDickens]

We're going to need a  bit more information to be able help you.

• What type of signal are working with.
• What do you want to limit it to.
• What version of LabVIEW and NI-DAQ are you using.
• What OS is this running on.
• Any other details that explain what you are trying to do.

Ed

[Peter8PG]

I am running Windows XP, LabView evaluation software and NI-DAQmx 7.5. I am using a USB6009 to acquire an analogue signal from the output of a DAT recorder,

The signal on the DAT recorder is that of an Electromagnetic Telecommunication device used in downhole drilling applications. It sends the data it logs to the surface in a series of pulses. The time between these pulses relates to a hexadecimal symbol.

The pulses sent to the are one second long and have frequency 5Hz. It is these pulses that the band pass filter is set to recover. I then half-wave rectify these and put this signal through a low pass filter. When a pulse is detected this produces half of a sinusoidal waveform.

The amplitude of this sinusoid is then compared to a numerical constant. When the amplitude is greater than the numerical constant the output is '1' - this gives a square wave everytime a pulse is detected.

I plan to output this square wave pulse to another machine running specialist software that will decode the pulses. It however, is very specific in the format of the pulses. They cannot be high for more that 0.5 seconds. What I want to do is detect when the output from the comparison block is high and generate one pulse that is high for 0.5 seconds. Every time the output form the comparison block is high, I want to generate one pulse that is high for 0.5 seconds.

Im sorry if that is rather vague or non-technical but I hope it helps you answer my question.

Peter Cruickshank

[Peter8PG]

My first post appears to have disappeared. It had my VI attached to it. I attach the VI I am using here.

Peter Cruickshank

[EdDickens]

Since it looks you're trying to output a TTL signal (the output is set to 0-5 volts), I'd say your best bet would be to use the Counter on the device instead of the Analog output. The Counter gives you very precise control of digital waveforms and their pattern/timing. And they work great for controlling the duty cycle.

Have a look through the examples to see how to use them. Once you get to know the Counter, you'll wonder how you ever lived without it.

Hope that helps.

Ed