Control Voltages

[bubzy]

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

how are you guys implementing CV in your projects?

[xi-boy]

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

[elmegil]

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.

[bubzy]

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
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

[blue hell]