Here's three possibilities:
In Method 1
, the schottkey diode prevents the input from going higher that 5.3V -- thus protecting the input. BUT, since the Sense Voltage shouldn't be going that high, anyway, Method 2
is a better choice -- just keep the Sense Voltage in a range between 0V and 0.5V.
BUT, because it's good to keep the Sense Voltage as low as possible, for a couple of reasons [see below], you'll want a bit of amplification before feeding it to the Arduino. Method 3 uses an OpAmp to achieve this. Select an OpAmp designed for a "single rail" supply, like that used on an UNO, with inputs that can go all the way down to Ground.
"n*10k", on the Method 3 circuit, means how many times greater than 10k that resistor needs to be, to achieve the amount of amplification needed. In other words, the amount of amplification is determined by the following formula:
R2 in this case, is the n*10k resistor. And, OK, yes...to say 'n' is the gain is an approximation [a very close approximation]. R1 of course, is the 10k resistor [the input resistor, whereas, the n*10k resistor is the feedback resistor].
Why keep the Sense Voltage low? So it doesn't steal power from the Load, and so it can be a low wattage resistor. Lower wattage shunt resistors [the type typically used for this kind of current sensing], are less expensive. BUT, use a high enough wattage so it doesn't heat up a lot, 'cuz there's more possibility the resistance will change, and skew the reading.
You might get away with an OpAmp that can run off 5V, but make sure the output can go high enough to satisfy whatever Analog Input requirement you have.
The diode pairs, shown in Method 2 and Method 3 can be the 1N914 or 1N4148.
Keep lines short and the circuit compact, in Method 3. also, if the Sense Voltages are very small, it might be necessary to cover the OpAmp circuit with a shield. This is typically done by making a metallic cap to cover the circuitry. I've used tin snips to cut out a form from tin plates steal, or copper foil. Then I fold it into the intended shape and solder it to ground traces on the PCB.
Note: In Methods 1 & 2, that 2k resistor is a bit conservative. It can, probably, go as high as 10k, without adversely affecting the ADC Sample-and-Hold. If a higher value is desired, then throw a 100nF capacitor across the Analog input. This will slow the response rate down, but will also double as a noise filter.
Note 2: The choice of A4 as the input, in all three of the circuit diagrams [above], is arbitrary. Any of the Analog inputs can be used.