How can I create feedback measurement with an operational amplifier? 0-20mA measurement
If your load resistor Rload can be &quot;floated&quot; so that neither end is grounded, the circuit becomes very simple.
As you say, a current-sense resistor (120 ohm) is used to sample transistor emitter current. Transistor collector current is very slightly smaller. Opamp must be of &quot;rail-to-rail&quot; type, because output voltages and input voltages can range anywhere from 0 - 3.3V:



simulate this circuit &ndash; Schematic created using CircuitLab
 However, if one end of your load must be grounded, the circuit becomes a little more complex.