Help with Atari Punk Console breadboarding

mbolis · Joined: Nov 17, 2015 Posts: 5 Location: Bergamo, Italy

Hello everybody,

I'm new on this forum, so first of all hi to everyone, I'm happy to be here! Very Happy

I'm breadboarding a Kaustic Machines Atari Punk Console as an absolute beginner project and I would like some helping input on an issue I have just encountered.
Looking at the APC output on Xoscope (oscilloscope on my Linux PC through audio-card), I can see it is not at all a square/rectangular wave as I expected, but instead some sort of skewed wave (as if a capacitor was leaking its voltage through to the output).
I'm attaching a snapshot of the wave as seen by Xoscope.
Not only this, but if I zoom in I can see many teeny tiny spikes that become denser and denser as I increase the astable's frequency.
Does anybody have a vague clue about what could be going on, and would like to help me troubleshoot this behavior?

Many many thanks, a nice day to everyone,

Marco

xoscope-apc.png

Description:

An example of the waveform I'm seeing coming out of my APC breadboard.

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42.17 KB

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162 Time(s)

This image has been reduced to fit the page. Click on it to enlarge.

PHOBoS

Do you have the capacitor on the output, or are you measuring the output of the 556/555 directly ?
If you have a capacitor on the output the skewed wave makes sense, if not it could be caused
by capacitors on your soundcard input. This might also explain the tiny spikes you are seeing.

mbolis · Joined: Nov 17, 2015 Posts: 5 Location: Bergamo, Italy

Ei hello!

Thank you PHOBoS.
Yes I put a 10uF capacitor in series with the output, but I suspect my soundcard has one, too.
So that skew would be some sort of high-pass effect?
Is there a way to counter it?

blue hell · Posted: Tue Nov 17, 2015 3:39 pm Post subject:

Yes the soundcard usually has one too, but it is not really a problem .. except you need keep it in mind when interpreting scope shots. There is not much you can do about it anyway, except for shorting the input capacitor of the sound card (and some people do stuff like that ... or find a DC coupled one, not sure if there are soundcards with DC coupled inputs .. they exist with DC coupled outputs tho ...).

But ..

looking at the image DC levels seem to flatten out in roughly 5 milliseconds (or a high pass roll-off of around 200 Hz) ... which seems too fast (too high a frequency) .. are you sure your capacitor is 10 µF? As it looks more like it is 10 or 100 nF or something ... don't take the numbers too exactly ... just used some rules of thumb to get an estimation ...

mbolis · Joined: Nov 17, 2015 Posts: 5 Location: Bergamo, Italy

mbolis · Joined: Nov 17, 2015 Posts: 5 Location: Bergamo, Italy

OK guys, I take my laptop's sound-card input has a 100nF or so decoupling cap, because I tried to measure the signal with my desktop PC and it does indeed look square.

Just one more thing I'm unsure of. As I turn the monostable-side pot up, I get an increasing voltage offset through the signal, is it normal?

Thanks again, everybody have a nice day!

Marco

blue hell · Posted: Fri Nov 27, 2015 3:59 am Post subject:

When the pulse to pause ratio changes the observed DC offset will change, yes, due to the capacitor again.

The capacitor causes the average DC level after it to be zero.

mbolis · Joined: Nov 17, 2015 Posts: 5 Location: Bergamo, Italy

Thank you.
The less I know, the more I understand Very Happy

Should a post like this be marked with some "resolved" flag, or something?