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)
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.