Arduino ProMicro Reference shifting? - Page 1
Forum section: electronics / projects

author: XantheFIN
author_rank: Contributor
timestamp: December 28, 2022, 04:39:57 pm
content: Issue: I get wrong voltage reading when certain situation and only bypassing Arduino's on board LDO/power circuitry fixed it finally to be stable.I recreate this article project:https://circuitdigest.com/microcontroller-projects/battery-internal-resistance-meter-with-arduinoAs i was needing one for testing cells... for at least show way when comparing many cells who is who.Unlike in there i use ProMicro and relay switch (single ready relay module) and in series for reading voltage (Input pin) is 1k resistor (i planned to give some protection for accidents)...Issue came up when it did read loaded cell voltage. It shows almost always higher voltagewhich breaks physics lawsI got it fixed only after i did bypass onboard LDO circuitry.. though i went further before that by read using Internal reference, taking multiple samples and averaging them...Why it reads unloaded Voltage normally but when during load test i get.. higher Voltage?Does power circuitry of this ProMicro start making Reference Voltage shifting or does ProMicro get just itself too loaded so it moves Reference too making bad reporting?Pictures attached.. the other one is now totally off but get point as V1 is not loaded and V2 is loaded Voltage..I just maybe need stop using on board power always then? I would want know just what happens exactly here so i can prevent this mishap in future more clearly as i am not 100% sure. Like i was not sure should i post in newbie section as this was project.

author: eugene
author_rank: Frequent Contributor
timestamp: December 28, 2022, 10:33:54 pm
content: Your ProMicro likely is running at 3.3V, which would be the reference voltage used by the ADC (ProMicro's are available in both 3.3V and 5V versions.). The project that you linked to uses 5V supply.As you found, you can safely run the ProMicro at 5V by bypassing the LDO.

author: XantheFIN
author_rank: Contributor
timestamp: December 29, 2022, 06:03:54 am
content: Hi thanks for answer.. i tried verify this too which one i using due both versions out there... RAW pin and jumper Pin both side were +4.5V and before regulator was 4.9V..But still even if it would be internaly running 3.3V why voltage jumps in under load (even with taking multiple samples) when it was and is using same reference (without reading reference voltage and or with reading reference voltage point on both time) all the time?Edit:: I feel dummy.. maybe the i am taking power for 5V rail wrongly which overloads LDO when relay clicks on that time.. will verify if it drops later of the day.

author: XantheFIN
author_rank: Contributor
timestamp: December 29, 2022, 06:27:08 pm
content: OkayActually now measured with LDO and the 5V output and relay pulling makes it drop significantly which i guess makes the Reference too does move then making measurement..So on board power circuit does kicks the bucket was the reason. Which then made Reference voltage shift too.Which was funny as i tried too while figuring out previously measure reference voltage on during both measurements to compensate any voltage shifting which didn't help.. so chip cannot adjust so well in all situations just i guess even via internal reference measurements or outside measurement reading. boo.This MicroPro i using is 5V always, there is no 3.3V going to chip anywhere even from LDO on these i have. I may forgot mention yes i did too "calibrate" voltage as "no load" voltage measurement was right