> Not having had experience of or use for 4-20mA loops before I've
> been looking around to find out a bit about them, as one is needed in
> a current (pun intended just for a change) project

Here's one way of doing it with cheap parts. This circuit is analog output only
(but 4-20mA input can be simple too). Hope it gives you some ideas.

http://www.piclist.com/techref/microchip/aout.htm?key=analog+output&from=

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Brent Brown, Electronic Design Solutions
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