No, every connection was tested and i have everything where it should be,
as in the links you sent me. I am not even touching the op-amp part, i just
measured the voltage right after the R-2R ladder without any amplifier
afterwards.
I think i will try to test the ladder using some jumper switches instead of
PIC pins, this way at least i will know is not a "not enough current" issue.


On Jan 23, 2008 5:26 PM, John Coppens <john@jcoppens.com> wrote:
> On Wed, 23 Jan 2008 16:39:02 +0200
> "Dumitru Stama" <spanac@gmail.com> wrote:
>
> > This is almost the value I should get by sending "250" to the DAC but
> > instead I get 2.35,
> > almost half of what it should be. Am i right here ?
>
> I'm guessing you are not connecting to the correct node of the R/2R
> network. 10k/20k should work well with the PIC outputs. Note that there
> are two different applications for R/2R: One uses an opamp at the output
> and works with currents
> (http://www.allaboutcircuits.com/vol_4/chpt_13/3.html)
> the other one is designed for volrages
> (http://www.avr-asm-tutorial.net/avr_en/AVR_DAC.html - note that the
> opamp here is only as a voltage follower, not current to voltage
> converter).
>
> John
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