Current signals of 4-20 mA are commonly used in industrial applications to transmit process signals to controllers. Compared to analog voltage signals or digital communication, the current loop provides several advantages. This project demonstrates how to derive it from a PWM output, which can be generated by any microcontroller.

The Project

The purpose of this project is to provide a 4…20 mA output from a PWM signal generated by an ATmega328 microcontroller (and numerous other chips, such as the PICs). One of the more interesting applications of this circuit would be to replace or to realize a smart sensor with Arduino.

The 4…20 mA standard was introduced a few decades ago, to replace the existing 3…15 psi pneumatic standard for controlling remote actuators. It soon became quite popular for its versatility and for the inherent robustness to electrical disturbances. The current loop between the transmitter and receiver is usually supplied by an external 24…30 V DC power sou...