What is an R/2R, how do i build one, and how do i use it?

Usedtobe

I get that it's DAC, but schematics i find seem pretty vague. like I could totally build one but i have no idea how to use it or what it really does.
thanks!

bought 4018s and 4051s, gettin em on tuesday. rad shit comin sooon

Inventor · Posted: Mon Nov 30, 2009 8:14 pm Post subject:

Here is the link that Jan gave me for an R2R ladder:

http://upload.wikimedia.org/wikipedia/commons/a/af/R2R.png

One thing you can do with an R2R is take a few Lunetta signals and connect them to the inputs. Then the output is a weighted sum of the inputs, creating potentially a more analog-ish sounding result. For this purpose I suppose it would be best to connect slow signals to the MSBs and fast signals to the LSBs.

Les

stolenfat · Posted: Tue Sep 14, 2010 1:24 am Post subject:

i want to try replacing the resistors with vactrols... any one give that a shot?

Im trying to figure out what to do with 10 4017 out puts....

adambee7 · Joined: Apr 04, 2009 Posts: 420 Location: united kingdom

Never tried vactrol r/2r. Give it a go and see what happens. I would make them myself as vactrols are really expensive. Its also known as a resistor ladder.

with 4017 i would use it for dividing pulses from clocks. Very Happy

stolenfat · Posted: Tue Sep 14, 2010 2:41 am Post subject:

whats a good value for r?

i got plenty of 1ks

DGTom · Posted: Tue Sep 14, 2010 3:01 am Post subject:

I dunno... a vactrol R/2R wouldn't have anyway to set the relationship between R & 2R... maybe strap the vactrol across fixed resistors... its alot of vactrols tho... yeah, I'd do photo-resistors in parallel with resistors & not have them enclosed with the LEDs, maybe bend them at right angles to point in differant directions, like Left for R / Right for 2R , use a few LEDs on each side, but this way the light "bleeds"

would def. make some wonky voltages!

actually... driving 10 LEDs from the 4017 & having those influance your photo-resistors could be kinda cool... chuck a bunch of other squarewaves into the R/2R inputs & have a big murky syncopated voltage soup Cool

edit; I generally use 10K or 100K for "R" but... with vactrols, I'd go as high as possible... 1M even.

adambee7 · Joined: Apr 04, 2009 Posts: 420 Location: united kingdom

I'd say 1M. I think most vactrols are 1M when dark anyway. Good idea for the 4017 have to try that. Very Happy