electronic tech question

[lee]

I downloaded a freeware oscilloscope program for my PC. It uses the "line in" on my sound card as the input. So far I'm OK (I think).

However, I want to look at AC signals primarily up to 4 volts, nothing larger than 8 volts, but the sound card spec is 0 to 2 volts.

I really don't want to fry my PC, so I'm wondering if anyone can help. I've thought maybe a simple voltage divider scheme might be OK, but that seems to limited and simple an idea. Please keep in mind I'm nearly an electronics idiot and I've no experience with this sort of thing (so please don't respond with something like - "just hook up a couple of flip-fops to an op amp and you'll be OK").

help (please).

[gl1674]

Yeah a divider of two resistors connected in series might work.

The only problem is in picking up the values of the resistors.
I'd start with a couple of 10kohm as ballpark to give you 1:2 attenuation or 30k/10k to give you 1:4 attenuation.
Since the resistance of the sound card is not known, you may get a lesser voltage on the sound card - it may drain it if it's resistance is low.

Also, depending on where you are trying to look the input resistance of your divider may affect the circuit you are connecting too. Proper oscilloscopes have resistance about 1 mohm.

[lee]

thanks.

The output impedance of the device I want to measure is 150 Ohms. The input impedance of the sound card is 47K Ohms.

If I understood, I would appropriately select relatively low values resistors (with proper divider ratios) and measure away, yes?

[gl1674]

Yep.

I'd still stay with the 10-40k range for the divider. Calibrating it based on a known voltage (alcaline battery + good voltmeter) is a good idea.

[lee]

thank you