How to Identify the input voltage range of PC Soundcard??

[themaccabee]

sound card input voltage

Hello,
I want to build an osilloscope..for detecting the serial dataoutput from a ckt transmitted at 38400baudrate..i d like to use xoscope http://xoscope.sourceforge.net
Can some body tell me whether it will harm my PC?what can be the voltage range given to my sound card,,how should i find it...?? mine is Intel 945GCCR board having a built in sound card..
Can somebody provide me more information regarding sound card based oscilloscope..??
Thank you.

 

[banjo]

sound card scope probe

Here is a scope probe designed for use with sound cards:

https://www.virtins.com/Virtins_Sound_Card_Oscilloscope_Probe_Manual.pdf

In this PDF they mention that the probe limits the input to the sound card to three volts max. I would suggest a three volt zener across the sound card inputs would limit the signal to +3V and -0.7V. Since you are interested in a digital signal anyway, any signal clipping by the zener will not be a problem. Use a 3K to 50K series resistor to limit the load on your digital signal.

 

[jhbbunch]

sound card audio input voltage range

I don't know that a sound-card is capable of handling 38.4 KBaud with no errors. It would have to be sampling a lot quicker than 44.1 KBaud.

 

[echo47]

sound card voltage input

That's right, the sample rate of most sound cards goes up to only 48 ksps. A 38.4 kbps signal would look badly jittery.
Some fancier sound cards go up to 96 ksps or even 192 ksps. The waveform would look better, but still jittery.

Also remember that most sound cards are AC coupled. An ordinary serial-port signal will probably appear sloped and bounce around a lot.

To check the sound card's input voltage range, you could simply apply a test signal (such as a 1 kHz sinewave) at various amplitudes, and watch for clipping in your sound recording program. Most sound cards will survive several times the clipping voltage without suffering damage, depending on the design quality.

 

[Slayerza]

sound card maximum input voltage

@echo47 would one not be able to do the reverse. Rather than determining the clipping voltage when applying an input voltage use an application such as winamp that allows software amplification. In this way the card's output would max out and you can verify the voltage using a scope.

Surely the card will not have a huge variation between the input port and the output port?

Cheers
Slayer

 

[echo47]

voltage input to sound card

It depends on which ports you are comparing. The microphone and line-in ports have very different input voltage ranges. The line-out and speaker-out ports have very different output voltage ranges.

The line-out and line-in ports may have similar voltage ranges under some conditions, or they may be very different, for example if the user simply moves the record level control. I suggest measuring the input range.

Another approach would be to read the sound card specifications, but unfortunately most sound card specs don't give much information.