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digital input to switch on and off analog output

On Programmer » LabVIEW

2,960 words with 3 Comments; publish: Sun, 18 May 2008 19:49:00 GMT; (200203.13, « »)

Hi,

I want to use a digital input to switch on and off a defined voltage at the

analog output. The voltage should only be on as long a high signal is at the

digital input. I need this relatively fast so I wonder if this could be con

trolled just by hardware.

Any help would be appreciated.

Thanks

Christian

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  • 3 Comments
    • Hi,

      I?ve attached a screenshot of a program that does something very close to wh

      at you?re asking. A pause trigger is used on one of the counter lines,

      which clocks the analog output. The digital input is what triggers th

      e pause. However, the

      analog output will not return to a known voltage ? you would have to add thi

      s yourself.

      On the other hand, this program would be very easy to create if you could ju

      st use software timing for the digital trigger. You could just read a

      Boolean, and then use a case structure to switch the different analog output

      voltages.

      Lastly, I would ultimately recommend using one of the USB relay modules.&nbs

      p; These are designed specifically for tasks like the one you?ve described.

      I hope this helps!

      Ed W.

      Applications Engineer

      National Instruments

      example.jpg:

      http://forums.ni.com/attachments/ni...9/1/example.jpg

      #1; Sun, 18 May 2008 19:50:00 GMT
    • Christian,

      If you really want it to work fast, you'd better try to use a MOSFET. Switch

      it on and off using the signal you want to apply to the input. Keep th

      e voltage on the Analog Output constant (the one that you defined). Plu

      g the transistor into your

      circuit, so that it would modulate the output voltage.

      If you send me more details about what you want to get I might be

      able to sketch a circuit for you. Typical response time

      of a MOSFET (a cheap one) is better than 0.5 us (and dow

      n to nanoseconds). &nb

      sp;

      Sergey.

      #2; Sun, 18 May 2008 19:51:00 GMT
    • Christian!

      I attached two easiest (up to me) variants to do that.

      The only thing is that the transistor will be open only while TTL is high. I

      f you can vary the length of the TTL pulse than it's fine.

      Another question is whether you need all that. According to your description

      (diode laser, CCD) you are doing some experiments in the lab. If so, y

      ou must have a pulse generator (if you don't have it, ask next door. This ki

      nd of stuff is available in

      EVERY lab). Trigger this pulse generator with your TTL and it will give you

      analog output pulse you desire.

      If there is no pulse generator available, than try with FET.

      In the scheme Rballast should be much greater than the input resitor of your

      laser (if it's 1 MOhm, take 10 MOhm for Rballast).

      Regards,

      Sergey.

      Scheme.jpg:

      http://forums.ni.com/attachments/ni...17/1/Scheme.jpg

      #3; Sun, 18 May 2008 19:52:00 GMT