EDIT: the project has changed quite a bit. jump to post #9 for details.
for a project i am doing i need to measure 4 current points using an arduino. i know that there exists premade solutions, such as the ACS712ELCTR-20A-T current sensor. however, i like to actually create circuits and try to understand them, rather than just using a off-the-shelf solution. also doing it this way will be cheaper.
so what i want to-do is have a circuit using a shunt resistor on the low-side (i.e. return current), and amplify it using an op amp. it will be a 24vac system, so a transformer isolates it from mains. also, the "drive" side of the design is completely isolated from the microcontroller side.
perhaps something like this:
i need roughphly 0-10A (7.5A theoretcal max), with resolution of +- 0.05A. i could live with +-0.1A resolution though.
there are lots of examples of this for dc:
since this is for a diy jbc soldering station, i figured i might use the design they used.
here is a link to a gallery showing the jbc design and my interpretation of it. it looks nothing like other designs, so they might be doing something weird. Gallery
any help/ suggestions for designs are appreciated. i cant find anything specifically for ac online. thanks!