Nick, for real low current, and if you take care of the inductive
kickback, you might be able to use a MOC3xxx series device directly.
Normally they fire triacs. They will run <30mA at 220Vac into a small load
if that's what you need. Read the data sheets carefully, there are some
gotchas when used like this.

For 5V several optoisolators will work. Look for a darlington type, it
will be more appropriate for a TTL level switch. Maybe take a DVM set it
on current scale and plug it in parallel with the switch. This will tell
you the current you really need to switch. I bet about 400 uA to 1 mA for
a LS TTL input with some internal pullup.

Peter

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