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Test Equipment Anonymous (TEA) group therapy thread

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ch_scr:
Maybe you're lucky and I was a bit too pessimistic: https://eu.mouser.com/ProductDetail/Bourns/4310R-R2R-103LF?qs=q1k7RwtO48gxHuVs5Nx%252BsQ%3D%3D

Edit: here are all the types: https://eu.mouser.com/c/passive-components/resistors/resistor-networks-arrays/?circuit%20type=R%2F2R%20Ladder

factory:

--- Quote from: Vince on March 21, 2023, 09:01:36 pm ---Thanks for the info.

5 Euros is quite expensive... for that price I guess I can easily find a "normal" DAC.

According to my stock spreadsheet, I have only one single DAC, just one.... in a cool CERDIP package so it's probably from you  :)

It's an AD571. Conversion time is 40us if my notes are correct.


--- End quote ---

AD571 seems to be analog to digital, datasheet states it features "low cost monolithic construction" looking at the price on Mouser I would disagree.
I've got the opposite, digital to analog in the form of DAC08, no idea if I have ADCs as very little has been listed in my spreadsheet.

There is no rush to choose parts from Mouser, I'm not in any hurry to place my order.

David

Vince:

--- Quote from: ch_scr on March 21, 2023, 09:11:09 pm ---Maybe you're lucky and I was a bit too pessimistic: https://eu.mouser.com/ProductDetail/Bourns/4310R-R2R-103LF?qs=q1k7RwtO48gxHuVs5Nx%252BsQ%3D%3D

Edit: here are all the types: https://eu.mouser.com/c/passive-components/resistors/resistor-networks-arrays/?circuit%20type=R%2F2R%20Ladder

--- End quote ---

Thanks for the links. 

I checked the first link before you edited your message. Looked at the datasheet and it says it's Thick Film which you said to run away from...
Also, datasheet says that tolerance is 2%.  That's atrocious in this day and age... and how can an 8 bit DAC even work with a 2% tolerance ?!

256 combinations, so each number is about 0.4% of full scale...

I guess I don't understand what they mean with their 2% "tolerance"... tolerance on what exactly ?

Maybe they talk about full scale ? So say if I feed the inputs with 5V logic chips, they mean that full scale might produce maybe 4,90V instead of 5V ?

If that's what they mean then I don't care, as the signal will be conditioned down stream anyway (scaled + adding an offset maybe, I don't know yet) .... what I care about is how well the resistors are matched, so that the linearity is acceptable for my application...

I will check your second link to see if I can find some 9 bit DAC in there.

But it's getting late so I will probably look into that tomorrow after work...


Vince:

--- Quote from: factory on March 21, 2023, 09:23:32 pm ---AD571 seems to be analog to digital
--- End quote ---

Geez you are right, made a mistake in my spreadsheet indeed !  :palm:
ADC it is, not DAC....
OK so I have zero DAC in stock then, problem solved...



--- Quote from: factory on March 21, 2023, 09:23:32 pm ---There is no rush to choose parts from Mouser, I'm not in any hurry to place my order.

--- End quote ---

Ah cool, thanks.
In this case I will take a few days to hurry up and start working on the project. A quick first pass, back of the envelope design so I can evaluate how complex it would be to implement a "normal" DAC.
If not too much trouble then might go straight for that and call it a day, but if it proves troublesome then I think I would just use cheap R-2R jobbies to just "get the job done"...
This would allow me to concentrate on the rest of the design, and once I have a working "proof of concept" board, I can always modify the design with a "proper" DAC later on, if really I deem the performance of the R-2R unacceptable after real world testing.

Vince:
I don't want to disclose my project, it's a secret but... I guess to help you understand the situation here, I am trying to make my design run with only discrete logic chips, no CPU or MCU, hence why the use of a  "normal" DAC is not very easy at first glance, since these things are normally meant to interface with CPUs, not home made discrete logic....

Now it's time for some sleep.....  :=\

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