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How to wire/GND everything correctly to get accurate ADC readings in my project?
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iMo:
You cannot get a really clean output from such an regulator (switcher->lin regulator). The noise of the switcher is pretty high energetic such it is not to filter to the levels a single linear PSU may produce..
OM222O:

--- Quote from: imo on May 28, 2019, 06:39:21 pm ---You cannot get a really clean output from such an regulator (switcher->lin regulator). The noise of the switcher is pretty high energetic such it is not to filter to the levels a single linear PSU may produce..

--- End quote ---

In most cases a bulk capacitor + MLCC takes care of this issue on the input. if the noise is too high, often a CLC filter is used:


A common mode choke can also be used instead of a simple inductor to further reduce noise.
nemail2:
oh thank you very much. now i have to spend money for two ADCs  :-DD

Sorry for the late response, didn't have much time for hobbying around recently.

I have now tested out the ADS1115 (because I already had it here, ready on a breakout board) and well.. it is more than good enough for me in differential mode (even single ended is really good). in single ended mode i get readings which are about 2mV off most of the time and in differential mode (even without any filtering, slapped together on a breadboard) I get sub-millivolt errors only, which won't be shown on the display anyway. that's definitely good enough for me.

I'm now kinda struggling to decide whether I should really use differential mode and use 2 ADCs (I need 4 channels, unfortunately) or whether I should just go with single ended configuration.

i don't think I'd want to afford the more expensive ADCs like the ADS1219, that'd be really too much, i think. especially if I had to buy two of them, let alone if I need more prototypes/revisions of my design. unsoldering those ADS1xxx to re-use them is no fun without proper rework equipment (without destroying or at least damaging them). I do only have a soldering station (at least a decent JBC one).

calibrating the DAC would be out of my capabilities as well, that's really just too high sophisticated for me and I can't squeeze it into my head, unfortunately. maybe another time, when my knowledge and skills have evolved.

i have searched for 8 channel ADCs like the ADS1xxxx series but the only ones I found were like TQFP64 style packages (although affordable, they started at about 8-9€). i don't think I want to use such a TQFP64 beast in my design...

also, i have already 4 ADS1115 lying around here (bare chips in a reel), so I wouldn't have to buy any of them, at least for the next two board revisions, if I go with the differential setup.

what do you think?

ps: differential setup would allow me to provide sense wire inputs which would go directly to the ADC's differential input pins. the + line would have the voltage divider + the series resistor for protection of course but what about the ground line? are there common protection techniques which I should utilize? what if I connect the sense lines in reverse polarity, i'd then feed way to high voltage into the completely unprotected, bare ADC pin?!

thanks again for all your advices, stuns me every time how much I can learn here and how people are willing to help.

attached two photos of the measurements which make me happy :) and how crude everything is wired together :)
OM222O:
I would personally use the differential method, even if it means using to ADS1115 chips.
Don't bother with 8 channels for now, cost of two separate ones is the same for the most part.

About connecting the voltage backwards: it causes no issues. the ADS1xxx family are bipolar, so one of the bits is a sign bit, so it can be both positive or negative. that makes your 16 bit ADS1115, a 15 bit ADC. I'm not sure if this is intended or not, but same is true for the ADS1219. it's effectively a 19bit ADC if you look at the ENOB table provided in the datasheet. I can only imagine the names come from that.

the ADC has input protection ESD diodes built in. the only protection needed is some series resistance to the inputs. 1K should be more than good enough. in the schematic I posted earlier, RN1 and RN2 act as series protection resistors AS WELL AS being a part of the filter circuit. hitting 2 birds with one stone  ;)
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