I've seen some other smart furnace setups before, but nothing with the new abilities since 0.13 yet.
So i've decided to give it a try and build my own.
The build is extendable and quite compact so you can just add more and more modules.
The combinator / logic part is only needed once.
Overview, my factory
Setup of both modules
The first module below on the left side is a set of logical devices.Basically we get input from the logistics network (red wire) and look if we have more iron or copper plates.
The lesser value gets compared to an arbitrary number (5k in this case). The value gets delivered via the green wire to the filter inserters.
So the furnaces will start and process the material we have less of, up to the set amount.
To work around some edge cases we have two additional devices in there. The constant combinator to prevent getting no material if we have zero of something. And the combinator with '=', to do something if we have the exact same amount of both materials.
Production statistics
The whole array of furnaces will just cycle between copper and iron, depending of the amount of both.Since I have seen some pretty huge smart furnaces with lots and lots of logic, I'm not even sure if this qualifies as one, but it seems to work quite well.
If you have some further ideas please let me know
One from me: Take a look if this also can process steel and with which conditions. I have not the max stack bonus, so this might be subject to change.
Comparator blueprint
Furnace module blueprint
