2 Jul
2006
2 Jul
'06
8:13 p.m.
On 7/3/06, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
Well... yes... I don't have enough analog theory in my head to come up with
the value of R... 2*R is rather obvious once you have R.
What I really
would like to find is a formula for calculating R2R
ladder values so that I could get a 0V-5V output from an 8-bit
parallel port. Constructing it is easy, once one knows what resistors
to pick.
Eh? The resistors in the ladder are R and 2*R, for some suitable value of
R. Just out of curiousity, why do you want to use an R-2R
ladder, rather
than a single-chip DAC? Commercial vector displays that I've come across
either used a DAC chip (Vectrex), a DAC module (DEC GT40), or a rather
complicated circuit with tweakers for the top 6 bits (HP 1350).
Two reasons come to mind - one, to make this a passive device off of
the parallel port that doesn't require an external power wart, and
two, because I'm at the South Pole and I have to work with what I have
on hand - there won't be another plane for nearly 4 months.
-ethan