[sdiy] Arpeggiator1 / Arduino UNO

[Rick Jansen]

> On 10 Apr 2015, at 11:09, Nantonos <nantonos at epona.net> wrote:
> 
> Hello Rick,
> 
> Friday, April 10, 2015, 10:26:36 AM, you wrote:
> 
>> No idea, and I don't care :-) All I want is 12 discrete voltages per octave.
> 
> You mean that they are going into a quantizer, so you don't care about
> accuracy as long as they are distinct?

Sort of, yes.

>> As far as I can tell, without actually measuring, the voltages are
>> reached quick enough, and are repeatable.
> 
> Filtered PWM is a trade off between lots of ripple (but fast) and
> little ripple (but slow and slewing). Without either a measured result
> or a theoretical analysis of errors, the actual response is just
> guesswork.

Well, of course I looked at the oscilloscope, to check if the ripple had gone. With the 480 Hz pins there was still a ripple, with the 980 Hz pins none is visible, on my old russian scope.

It's not guesswork entirely, the 10uF/1k resistor result in an RC time of 10ms for rough settling. That order is good enough for note playing, I think, so far.


>>> On 10/04/2015 10:08, Roman Sowa wrote:
>>> How does your 8+8 bit PWM DAC perform in terms of DNL at the MSB
>>> boundary? I mean when for example it goes from 40FFh to 4100h, as well
>>> 4000h to 3FFF.
> 
> I would be surprised if the ENOB is even as high as 12; probably more
> like 10. Which is fine if it suits the purpose, but describing this as
> "16 bit" is misleading for anyone else thinking of building it.

That is why I labeled it "~16 bit DAC" :-)

Even an 8-bit (ZN426) DAC would have been good enough, it will give you 256 discrete voltages. If you choose the reference voltage and scaling right you will end up with a 83.3 mV per note characteristic..

Rick


> 
> 
> -- 
> Best regards,
> Nantonos                            mailto:nantonos at epona.net
>