Can I plug a TTL signal into the mic on my sound card?

[josborne]

Basically I want to trigger some LV code using an incoming 0-5 volt TTL signal.

And I was wondering if I could plug that TTL signal into my mic input and read the signal with the LabVIEW sound VIs.

But I'm unsure if I'll just end up frying my sound card.

I know I could buy a cheap NI USB DAQ board for $99 ... but I just want to get this done asap, and thought the sound card idea might work.

Any ideas?

[Coq_Rouge]

A sound card is AC coupled. And has limited  bandwidth. So I will say this is a far from optimal solution. What are you trying to do?

Sound cards are most often made for line-in signals levels. That is +/-1 volt. But this may vary from vendor to vendor.

[josborne]

Thanks.

I am trying to trigger some LV code when I receive a high TTL trigger signal from an external system.  The external system is from a third-party vendor and I can't really mess with it.  It outputs a TTL signal and I just want to run some LV code when the signal is high. 

Was just wondering if I might be able to input it to the sound card and trigger my code that way.  But I guess I might just buy one of those cheap USB digital I/O cards from NI.

[johnsold]

You can always attenuate the pulse to the level which the sound card can handle.

The bigger issue is what the sound card will detect with a pulse input.  You will have one rising edge and one falling edge.  The rise and fall times likely correspond to frequencies much higher than the bandwidth of the sound card.  Depending on the pulse width the spectral content could be above, below, or within the sound card bandwidth.

More questions than answers.  Likely a DAQ card is a better choice.

Lynn

[NIquist]

Why not just use your PC's parallel port?

http://digital.ni.com/public.nsf/allkb/B937AC4D8664E37886257206000551CB?OpenDocument

[tstahl]

Trying to remember the last time I saw a PC with a parallel port...

[NIquist]

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@tstahl wrote:

Trying to remember the last time I saw a PC with a parallel port...

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Probably the last time you looked at any PC.  It's the DB-25 connector, also called the printer port.

[tstahl]

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@NIquist wrote:

Probably the last time you looked at any PC.  It's the DB-25 connector, also called the printer port.

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heh... Guess I've been looking at too many laptops lately.

[Cory_K]

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@NIquist wrote:

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@tstahl wrote:

Trying to remember the last time I saw a PC with a parallel port...

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Probably the last time you looked at any PC.  It's the DB-25 connector, also called the printer port.

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You'd be suprsised. Its actually relatively difficult to come across a computer with a serial port, unless you go out of your way to ask for one.

[josborne]

Hmmm ... Could I wire this input signal to one of the status lines on a serial port port?

For example, could I wire it to the CTS line and read that line using NI-VISA?