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 Forum index » DIY Hardware and Software » Arduino
Control Voltages
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bubzy



Joined: Oct 27, 2010
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PostPosted: Mon Aug 20, 2012 11:27 pm    Post subject: Control Voltages Reply with quote  Mark this post and the followings unread

Right,
so having locked myself in my room for the past few weeks building an arduino cycle computer, i have started to turn my attention to using it in a synth environment.

so as always i have a question :
if i use the pwm via a simple resistor/capactior filter am i going to lose voltage through the filtering?

my first project will be a v/oct calibration device which should be simple enough Razz

how are you guys implementing CV in your projects?

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xi-boy



Joined: Dec 16, 2008
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PostPosted: Mon Oct 08, 2012 8:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

i use a inexpensive 12bit dac (MCP4921)
as described here http://mrbook.org/blog/wp-content/uploads/2009/06/gakkensx150mod4.png
http://mrbook.org/blog/2009/06/27/sx-150-synth-mod-schematics/
i didnt get a clean cv voltage out of the pwm
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elmegil



Joined: Mar 20, 2012
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PostPosted: Tue Oct 09, 2012 2:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

The only CV I'm generating with Arduino is in my port of the TH MTS-100 MIDI->CV module, and I used the 8bit DAC he used in his original design. I've heard the same about PWM CVs though, that they aren't clean enough to do good 1V/Oct.
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bubzy



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PostPosted: Tue Oct 09, 2012 11:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

i've actually managed to get perfect cv out of the arduino.
it requires a bit of fiddling and there is a trade off.
you have to increase the pwm clock so that you get about 62.5hkz pwm frequency, the trade off of this is that is screws timer0 up, not entirely but it does it to the point that you have to use
delay(64000) to delay 1 second Smile
this is then filtered through a low-pass RC filter and is a nice clean signal.
it is not very good for LFO operations however as the pwm is still only 8 bit so there is quite a lot of stepping on "waveforms", could be worked around with a larger capacitor in the RC filter, but then you have to contend with lag.
as it is though, its prefectly good for 1v/oct, more soon in my seq thread Smile

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Blue Hell
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Joined: Apr 03, 2004
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PostPosted: Wed Oct 10, 2012 11:19 am    Post subject: Reply with quote  Mark this post and the followings unread

bubzy wrote:
it is not very good for LFO operations however as the pwm is still only 8 bit so there is quite a lot of stepping on "waveforms", could be worked around with a larger capacitor in the RC filter, but then you have to contend with lag.


Or make the signal a bit jittery maybe ... for instance to make a value of 1.5% you can alternately put out 1% and 2% .. when the PWM rate and the jitter is high enough that might just work (not that the numbers I used for the example wsould be very practical, but you get the idea probably).

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