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Quick electronic question

I need a 20k R2R resistor network (for making another project on the net) and I'm ordering from mouser and the only ones they have are out of stock, so I want to build one. I know how to hook the resistors relative to one another (a quick look at wikipedia solved that), the only thing I'm wondering about it the values... To make a 20k R2R network do I need: 10k and 20k resistors? or 20k and 40k resistors? I think it's 10k and 20k, but I'm not sure

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westfw8 years ago
I'd say if it's called an "R2R network" and labeled "10k/20k", than R=10k and 2R=20k...

Note that for D-A usage like this, you can pick "any" value of R, and it's pretty common to use a batch of resistors with value "R" (using two in series to get the 2R values. This way you probably get a bunch of resistors from one "batch" that are pretty closely matched.)
NachoMahma8 years ago
. Maybe this PDF on R/2R Networks will help.
guyfrom7up (author)  NachoMahma8 years ago
I read it... and it didn't really help...
. Sorry. I couldn't find anything on what defines a 20K network. If I had to guess, I'd say that for a 20K network R would equal 20K (why name it after 2R?). so 20K and 40K resistors.
guyfrom7up (author)  NachoMahma8 years ago
alright, I might just go with that, it does make more sense
BTW I'm making a function generator following this page:
http://www.myplace.nu/avr/minidds/index.htm

On the schematic it says 10/20k, I don't know if that means 10 and 20 k ohm resistors, or 10 pins, and it's a 20k R2R

also, on most projects online that use a R2R it consists of 10k's and 20k's

A lot going on here...
guyfrom7up (author)  guyfrom7up8 years ago
also could I change the AT90S2313P in the design with a more modern ATtiny2313 or do you think I'll run into problems?
Based on the schematic you posted I think it calls for R=10k, 2R =20k. As far as specifying the network goes, I believe (I only found one vague reference in a data sheet) that it would be defined by the value of R. The output of the ladder always sees and equivalent resistance of R. Plus, like NachoMahma said, it doesn't make much sense to name it after 2R. Whatever values you choose to go with should be fine though, because the values of R and 2R do not change the value of the output.

The ATtiny2313 is a direct replacement for the AT90S2313 so it should work fine, but there's some things you'd need to watch out for that you can find here. Looking at the asm code I think there's a few register names that will need to be changed and the right fuses might need to be set, but I'm by no means an expert on asembly (or a novice for that matter, I can loosly follow the code but that's about it). Someone proficient in assembly should be able to use the link I posted to figure out exactly what changes need to be made.
> On the schematic it says 10/20k...
. I've never worked with R/2R, but I'd say that means 10K and 20K resistors for R and 2R, respectively. But the network shown does have 10 pins.
. My guess is that as long as all the R's are the same value and all the 2R's are twice that value, it ought to work at least well enough to give you some kind of reading.
.
> could I change the AT90S2313P...?
. I have no idea. That's waaayyy over my head.
Reziztorz iz wutz? Just kidding. I'm bored.