Sawtooth looks fine, but square looks weird
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Sawtooth looks fine, but square looks weird

by Kyrigo on Sun Jul 01, 2012 9:11 pm

Hi,

I'm building my first x0xb0x using the Willzyx kit, and I could use a little help: I built up the power supply and just finished the VCO, but my square wave is looking a little sickly on the scope. I just triple-checked all the components and didn't find anything amiss. I've attached pictures of both waveforms and some pics of the main board so far -- If you have any idea what might be wrong, I'd be really grateful to hear it.

Saw wave: http://i.imgur.com/D35GG.jpg
Square wave: http://i.imgur.com/8gNnZ.jpg
Front of board: http://i.imgur.com/BzC1n.jpg
Back of board: http://i.imgur.com/t8Xm2.jpg

If you need me to take any readings, let me know. I'll just continue with the build for now.
Kyrigo
 
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Re: Sawtooth looks fine, but square looks weird

by antto on Mon Jul 02, 2012 1:30 am

if that is at ~9Hz then it looks fairly okay for the square, you should know that the 303 square wave is actually NOT a square at all
if you are still not sure - post a picture of it at some higher frequency like 50 - 100Hz
but i'd say don't worry, continue with the build
We are here too: irc.freenode.net >>> #x0xb0x
..:: c0nb0x v1.00 ::.. http://forums.adafruit.com/viewtopic.php?f=7&t=29282 (new control app - win/osx)
VCO Tuning: http://forums.adafruit.com/viewtopic.php?f=12&t=24759 (do it the EASY way)
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Re: Sawtooth looks fine, but square looks weird

by Altitude on Mon Jul 02, 2012 8:02 pm

Yeah, the term "square" is pretty loose when it comes to the 303/x0x. Use your ears first
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Re: Sawtooth looks fine, but square looks weird

by Kyrigo on Mon Jul 09, 2012 7:20 pm

I upped the frequency to ~100Hz and the waveform looks great. Thanks!

Unfortunately this also brought another problem to light: the VCO frequency is WAY off what the instructions predict. The manual says to apply 3V DC to R90 to get an output of around 150Hz... I only get around 6Hz. To get 150Hz I have to apply about 7.5V DC! What can I do?

Edit: ugh; something seems to have gone bad with the power unit since I last worked on my x0x. Now J4 is giving me 9.4V, 0v, and 20.8V(!!!) instead of 5.33V, 0V and 12V. It was working just fine last time. From the FAQ it looks like this is due to a bad LM336. I ordered a replacement. However the VCO issues were happening before my power supply woes, so my question still stands.
Kyrigo
 
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Re: Sawtooth looks fine, but square looks weird

by MMM on Thu Jul 12, 2012 9:27 am

At this point I'd suggest getting the power supply problem fixed; and then we'll trace further from there.
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Re: Sawtooth looks fine, but square looks weird

by Kyrigo on Fri Jul 13, 2012 4:00 pm

Okay. I replaced the regulator and the power supply is back to normal. I'll do some testing on Monday to see if I can replicate my VCO frequency problems.
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Re: Sawtooth looks fine, but square looks weird

by Kyrigo on Thu Jul 26, 2012 6:15 pm

Well I fixed the power issue and the frequency issue magically resolved itself. Aren't electronics great?

Looks like I'm done with the analog section. Onward!
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Re: Sawtooth looks fine, but square looks weird

by MMM on Fri Jul 27, 2012 5:16 am

Kyrigo wrote:Well I fixed the power issue and the frequency issue magically resolved itself.


This isn't totally surprising since both the 5.33v and 12v supply voltages are also used to create a "voltage offset" in the oscillator. So if even one of them is widely out of spec this will strongly affect the tuning.

Good to hear you're making progress; and good luck with assembling the rest of your xoxbox.
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