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I have Arduino Uno connected to a computer with a USB cable. Then I have a DC circuit, powered by a wall adapter.

In this circuit, I have a shunt resistor (connected in series after the load) and I would like to measure the voltage across it with the Arduino analog pin.

But I am unsure if, or how this will work. Since the computer and the circuit have separate power sources, then their grounds aren't common. Does that mean it won't work? I am too afraid to connect the grounds because I am scared of frying my PC.

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  • \$\begingroup\$ Are you measuring the voltage drop across resistor to estimate the current through the load, then send the measurement result through USB? Is that all that you need to do? If so, what's the range of currents that you will be measuring? \$\endgroup\$
    – Nick Alexeev
    Nov 18, 2018 at 22:29

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You need implementing a 'probe' like at the inputs losing some precision digits but gaining conformance from two different systems. Otherwise you need a complex differential inputs at the ADC which may be effortless.

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