[sdiy] minimalist resistor ladder DAC intonation

[Jason Nanna]

Hi, I'm looking at building a minimal resistor ladder DAC as an
experiment with a Raspberry Pi.

I was hoping someone might have some ideas with respect to
temperament.  What I'd like to accomplish is a direct bit-to-interval
relationship, so for example the LSB would correspond to a semitone,
the next-LSB would be a larger interval which could have the LSB added
to it to achieve the third pitch, and so on.  Perhaps the LSB has to
be a microtonal interval to 'correct' certain others.  I'd like it to
be 8 bits.

I don't require a general-purpose scale.  I'm looking for something
musically useful.  The octaves do not have to be 2:1 per se, and I
don't need a wide range of control voltage.  The GPIO pins are 3.3v,
so I presume I'm going to have to scale the DAC output up to 4 or 5
volts, which would be the maximum control range I'd expect.  Even 3
octaves would be sufficient.  The music will (hopefully) suit the
tuning, not the other way around.

Hoping to get interesting ideas.  Perhaps someone knows of a similar
project, but I haven't been able to find anything online to date.