I am trying to make a voltmeter for a power supply.

Hello

I am trying to make voltmeter with Arduino and ADS1115, for a power supply that I have.

The power supply that I want to measure has variable voltage output 0-25V.

I am using a voltage divider with R1=20k and R2=5k resistor.

I tried differential measurement between the voltage divider output(DividerValue) and negative output of the power supply(GND) but I couldn't make it work.

Arduino and ads1115 is powered up by usb or a small 5v wallwart.(5V and GND1)

EDITED:

I tied Arduino gnd(gnd1) and power supplies negative (gnd) together. Now differential measurement works.

Won't the differential measurement work without common ground?

How can I improve precision I measure with Arduino 20487.xx-20490.xx.And with multimeter i measure 20.44.

code: https://pastebin.com/k0HKRUrn

Schematic

https://preview.redd.it/bwlv406udur61.png?width=1117&format=png&auto=webp&s=ea5d895d8b529ddf150044e024ca07d6dc41655e

Touch here for the full post on the Arduino Apprentices tumblr

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