INTRODUCTION
In order to understand how a 4-20 mA current transmission is control and how it works,
We are going to make a device that controls the 4-20m amp with the help of a transistor, LM358 and resistors. as shown in circuit diagram
Circuit diagram

Connection with Arduino
We are giving PWM ( Pulse Width Modulation is a technique for getting analog results with digital means. Digital control is used to create a square wave, a signal switched between on and off. This on-off pattern can simulate voltages in between the full Vcc of the board )
Through the pin 3 we give the pwm to the the +ve side of the op-amp as input
Schematics diagram

Simulation
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