Re: Stereo Scoundcard Oscilloscope

The one interesting feature is "AC/DC". Beats everything.

Cheers!

The other nice feature is that Bob doesn't SPAM usenet, unlike Scott who has been a busy little spammer over the last week, in multiple groups.

Jon

ok, I'll bite. How do you do AC/DC on a soundcard for $9.95?

That was a tongue-in-cheek comment. Soundcards don't process DC.

Cheers!

Method 1. DealExtreme was selling USB sound dongles for under 3 bucks, jump the caps and set the offset in software..

Method 2. Which is what I have done before.

Data flip flop with Q/ back to D via a R divider. Sound output on one of the channels plus Zener shunt on the clk input for the PWM set at some high freq rate. Perform Pm detection... The input is at the Data input network, you are simply modulating the PWM and output (Q) is doing input to the sound card. etc..

I made a Data logger using method two, for monitoring DC and variations. Of course, I alway wrote the software for it...

For any one thinking about doing this via a D-FF, you may want to consider using a comparator at the D input, the threshold tends to drift a bit over temperature ranges..

Jamie

My (modified) sound card works to DC:

Or, build a chopper amp: (I haven't tried this).

Using a USB soundcard with modifications looks tempting. Just needs a bit of attention, as there is no protection against negative input levels. Can be nice to have around for monitoring logic signals.

Cheers!

Do you all really believe there is a DC blocking capacitor INSIDE the soundchip ?

Really ?

I don't. I can repair dual rail guitar amps and get 0.0 VDC at point X.

The point/question kinda is, if you fed the pin of the IC directly, would it register DC ? Possibly not, it may be designed to ignore DC, software wise or otherwise.

IF however, it is just a matter of a cap, you could concievable jump it out.

It may or may not work, that is the question, would it ?

Most if not all have a cap on the input. The chip does not have a blocking cap! That is blatantly obvious.. It's the circuit that leads up to the input of the IC.

And the reason you ask for this? couple of reasons, first the IC's input for the most part can't sit at 0 volts, unless you have a high end unit using dual rails, and I don't see that happening.

So you need a DC blocking cap for that any way, but another very important reason there is a DC blocker is due to the fact that many sound cards have a low current DC present at the tip of the input so that you can power up a small microphone and that simply gets modulated via this DC current. So you can see the reason the CAP would be needed here too.

When removing or jumping the cap you need to make previsions to handle input offset problems and the DC supply for the external mic.

Jamie

That's what I figured.

If it had a JFET input though it technically could...