hooking up breadboard oscillators to computer Line In safely without clipping?

[dentaku]

I started messing with a 555 recently (very new to this) and I managed to get this circuit hooked up to the Line In on an old computer instead of just using an old  salvaged 8ohm speaker like I did at first so I could see what it looked like with the s(M)exscope VST http://bram.smartelectronix.com/plugins.php?id=4 and add effects to it. At first I ended up making a triangle wave (by accident) but later I dismantled it and made a regular square wave that could be pulse width modulated.

There's lots of info and making oscillators and basic synths online but nobody shows how they hook them up the their computers to record the output.

What's the best way to do this so that the output isn't too loud or noisy? I got it working well enough by turning down the gain on my line in all the way down to 1 but I'm assuming there's a better way?
ALSO, I'm obviously working with DC here running from 4 AA batteries but audio signals look like AC to me. What should I know or what should I read so that I can understand how this works?

I really would like to make a VCO with an opamp sometime like I've found in the LM324AN datasheet and hook it up to my old computer. Programming synths and making sounds is easy enough because I've been doing it for years, it's building sound making devices that's completely new to me.

[SeanB]

Normally the line in has a maximum rating of 1V or so, and is almost always going to be AC coupled internally. You need to attenuate the voltage fed to it, using 2 resistors. A series resistor of 10kohms or so ( anything between 8 and 20k will work) and a resistor across the input of the sound card of around 2kohms ( again any value between 1 and 3k will do) to attenuate the input to something the sound card will be happy with.

[dentaku]

Normally the line in has a maximum rating of 1V or so, and is almost always going to be AC coupled internally. You need to attenuate the voltage fed to it, using 2 resistors. A series resistor of 10kohms or so ( anything between 8 and 20k will work) and a resistor across the input of the sound card of around 2kohms ( again any value between 1 and 3k will do) to attenuate the input to something the sound card will be happy with.

OK, a 2kohm resistor going to the tip or ring of the 3.5mm cable I'm using is easy enough. I've got a nice little 3.5mm jack I salvaged from something that plugs perfectly into a breadboard.

But, what do you mean by "A series resistor of 10kohms or so"?

I've been reading some more and it looks like somewhere between 0.5 and 1V is what most onboard line in jacks on generic PCs accept.