# Oscilloscope for windows

#### terrakota

Joined Feb 8, 2005
67
Hi, i have an old computer and want to try the oscilloscope project, but before start i have some questions:

whats the maximun frcuency you can measure with the computer sound card without damage? whats the maximum voltage signal to measure? is 120 v 60hz too high to measure with a sound card based oscilloscope?

#### beenthere

Joined Apr 20, 2004
15,819
Hi,

Stereo sound is usually digitized at 22.1kHz, so any one signal would get sampled at half that frequency. The sound card is designed to handle line-level signals, which would be about a maximum of around 1.25 volts RMS. So the 60 Hz is no problem, but the 120 volts willl have to be isolated and reduced in magnitude. The isolation through a transformer will keep the line voltage from turning the computer into smoke and junk.

#### terrakota

Joined Feb 8, 2005
67

#### audiophile

Joined Nov 20, 2005
1
hello,

could you please explain how you can measure electric signals thru the sound card, ie use the pc as a scope? (i'm wondering how you'd make the actual connections to the probes or whatever you'd use to measure.) Newbie here, thanks a bunch!

#### beenthere

Joined Apr 20, 2004
15,819
Hi,

The input connector to the sound card is a stereo 3.5 mm plug. I don't recall which channel is tip and which is ring.

Obviously, the input levels are going to have to be close to 0 dB for full scale digitization. I think that will be 1.35 vrms. The input is not very resistive, so things like 10x probes won't work without some external circuitry. It might be easiest to make a metal box with connectors for the probes, and internal pots for adjusting the signal level down to something that won't clip.

#### italo

Joined Nov 20, 2005
205
Originally posted by terrakota@Oct 28 2005, 10:31 PM
Hi, i have an old computer and want to try the oscilloscope project, but before start i have some questions:

whats the maximun frcuency you can measure with the computer sound card without damage? whats the maximum voltage signal to measure? is 120 v 60hz too high to measure with a sound card based oscilloscope?

if you use a PC for it seems a total waste of components. and will never surpass the quality of a 100 mhz analog scope and it is cheaper. an old tektronic cost only $400 a PC cost what? and it will be a sampling scope anyhow no matter how fast. there are some ancient software programs to use a PC for that for$500 so now you decide.