collecting through microphone port

[Gorelick]

I would like to record a voltage signal through the phono microphone port on my laptop.Could you tell what the port # is to do this and if there are any potential problems with this method?

[LesHammer]

Normally the sound card (microphone) is on port 0. (At least on my laptop.)

As far as potential problems, I assume that when you say "record a voltage signal" that you are recording something other than a normal microphone - i.e. connecting up a real voltage. If it has too high a level (or DC offset) you could fry your PC. If that's not a concern, the answers you get are in DAC values, not volts. You need to do your own calibration - which will need to change if anyone/anything adjusts the microphone volume settings. If that's not a concern, note that your PC's sound card may have low and high frequency roll-off, and might not have very good frequency response in general, and might not be linear.

If you would like to take a quick look at what your sign
als look like, www.CompleteTest.com has a PC Scope on its Products page. The PC Scope uses the microphone port as an input and displays the signal on a scope-like display. It is written in LabVIEW 7.0. You can use it free for 10 days.

Les Hammer
Complete Test

[rolfk]

Les Hammer wrote:

> If that's not a concern, note that
> your PC's sound card may have low and high frequency roll-off, and
> might not have very good frequency response in general, and might not
> be linear.

Yes this is very important. Audio inputs are usually limited to a
frequency range of 20 Hz to 20 kHz. As long as you only want to read in
audio signals the only other problem might be the accurracy which
despite of 16 bit delta sigma converters is usually not very high. That
is not a problem for audio signals as the absolute accuracy of the DAC
is not important here.
However if you want to read DC or near DC voltages (also temperature
signals for instance) you will measure basically nothing at all, since
the input can't see the DC part of the
signal.

Rolf Kalbermatter

[Gorelick]

Thanks for your input, I think from your suggestions that the mic port is not the way to go for this application. I have a one channel parallel port data logger which could be used. Thanks again!!