Thanks for the feedback, change in resistor value has been noted! The Opto in question is a Sharp PC120, and according to the datasheet the rated input If is 50mA absolute maximum. I’m giving it 22mA, should be fine I think, as long as it fires!
As for the load, it’ll be resistive (a hot wire ignitor), so I’ll be drawing quite a lot of current but for a very short amount of time. My MOSFETs are over-spec’ed for the application, 60V/30A max, but I’d rather have over than under.
I might put a flyback diode on there anyway… I guess you’re right that I don’t REALLY need the opto, but I thought it might be handy to make some little “breakout boards” that could drive most loads safely with no danger to whatever arduino board I happen to be using. A sort of “one size fits all” drop-in module. So as I had a couple, made sense to experiment!
You say it’s unusual to use it that way? Out of curiosity, what would be the “usual” way of doing it?