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adjustable digital input voltage

Hello,

I have a 9402 DI card I'm using in a 9139 cDAQ. I'd like to take some PWM voltage measurements and do some sort of counter scheme to back out RMS values, harmonics, etc. However, the voltage is (nominally) 220 V (on), and all I have are 100x attenuation probes, knocking my "on" voltage to ~2.2V (well below the "on" level for traditional 5V TTL). Does anyone know if there's a way to adjust the on/off threshold voltage for a 9402 card (or just general LabVIEW tricks with DI/DO)?

Thanks!
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Hi,

 

The specification of the 9402 says; 'Input high, VIH ...........................2 V min' so with 2.2V it just might work.

 

You say '~2.2V' which tells me that it is AC. Since it is PWM  assume it is DC.

 

You could also use a resistor divider to get a 5V signal. With a resistor of 4.7k and 205k in series you have a 4.9V signal over the 4.7k resistor.

 

Kees

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Hi Kees,

The "~" means (in Yellow Dart speak) approximately. I know that 2.2V is right on the edge of the typical TTL threshold. I'don't like to be able to run off of a lower bus voltage as well (maybe 180 or so), so I was curious if there was a way to adjust it well out of the way (maybe 1V or so). It'd be a lot easier than setting up a divider if it were possible, but if not then, given just my 9402 and a 100x attenuation probes, it might be my only solution.

Thanks!
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*I'd like to
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As far as I know the voltage of the digital input is not adjustable.

I think the easiest solutions are:

 

-1-

Use a daq with a analogue input and the 1:100 divider you have.

 

-2-

Built your own divider but less dependent of the input voltage. I think this can be done with a few resistors and a zenerdiode.

 

Kees

 

 

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Another option is to use a comparitor chip.  You can set your own threshold level and the output of the comparitor is a true TTL level.


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