[sdiy] PWM from a Micro as a CV source?

[ChristianH]

On Fri, 13 Jun 2008 12:34:08 +0000 Justin Owen <juzowen at googlemail.com> wrote:

> Hey all,
> 
> I'm after some advice on using PWM-capable pins from a Micro (probably the ATMega168/Arduino, and possibly via a TLC5940 LED driver) as a CV source.
> 
> The oscillator I'm using at the moment has its Pitch and PWM controlled by two HF113 Optocouplers, each sitting in the negative feedback loop an Op-Amp to make the control linear, which is fed a control voltage - which at the moment is basically pots set up as voltage dividers.
> 
> I'd like to replace the pot/voltage dividers with PWM outputs from a Micro.
> 
> Are there any reasons why this shouldn't work?
> 
> Would I need a Low-Pass filter of some sort on the PWM output?
> 
> All the info I've seen says it will control LEDs just fine - so therefore it should drive an Optocoupler - just wanted to see if there were any problems I might not have thought of.

Most probably you will need some filtering. About the only situation
where they can be omitted would be for dimming visible light LEDs, in
this case your eye will do the filtering (not counting those shoddy, um,
hi tech car rear lights - at some 30 Hz, no human eye is bad enough to
miss the periodic flashing).

But when controlling analog circuits, there has to be a lpf to make a
steady cv - unless you go way beyond your signal frequency (doing
something like in the current Buchla 257 thread), but then you'd have to
filter the signal itself to remove the switching frequency.

Christian