INA219 - Common Ground with MCU?

[Lisa76361]

Hi,

I am in the process of researching for a power / current measuring data logger.
I will be using Arduino MKR Zero because of its onboard microSD card slot.
My design looks like this.

In order for the INA219 to function properly, the power source being measured must share a common ground with the MCU. I assume this is correct, please correct me if I am wrong. I hope bringing the negative 24VDC to the MCU’s ground won’t cause issues to the board.

After reading someone else’s project who developed a module that has an isolated measured voltage so the INA219 and the MCU won’t share a common ground, I am confused whether or not I am on the right track. Thank you so much for any feedback!

[Clinton]

Hi Lisa,

Yes the common ground is the best way to go and will result in the most accurate measurements. The other tutorial is for making an isolated current measure, this can be useful when working with floating circuits (Ones that have no gnd connection) or in cases where you want the MCU not to be linked with the load.

[Lisa76361]

Hi Clinton,
Thank you for your answer Just want to clarify that the 24VDC power is supplied by a power supply that is plugged into the main 240VAC and it outputs 24VDC 20A. The common gnd therefore will be the negative wire of the power supply. The power supply of course earthed at the wall outlet.

Knowing this, is it still safe to have a common ground the way it’s shown in the diagram or better off using the other design with the isolated output?

[brian86770]

unplug the power supply from everything…
with a DMM set to resistance scale and or a continuity setting…

if you have a mega meter if you know what one of these is you could check how high the resistance is…
typically between the negative and earthpin…

test between the earth pin of the power plug and the negative output of the supply if you find that there is no resistance then that is not good at all …
this means that there is a connection between the negative output and the ground input…

eg …if the resistance is in the mega ohms…and if you have the meter set to test for continuity…and you have no continuity …then the negative output is not tied to the earth

if you are using a brick switch mode you will find that it may have a singe transformer or several of them
depending on the supply… there will be bypass filter capacitors to ground in several places…but generally the negative of a supply is not tied to the mains earth…it`s not done normally…

even if you fit an extra mains isolation transformer …you can still get electrocuted ,

…generally the earthed supply`s are earthed to find short to earth …should a short occur in the primary/secondary side of the supply…