Creating a 4 - 20 mA loop from an Ardunio Mega

I would like to control an AC pump and it requires a current loop to do so.

I found a board online but it looks very complicated to program, however if anyone knows how that would be great?

If not, I read that these circuits can be made using a few components. What is the best way of doing this and then implementing it into a code?

I have just been looking at this