Re: 300 mA from a microcontroller pin


Been there, done that. I have a full set of tri-state boosters in my
furnace, for driving the remote thermostats:

http://www.delorie.com/house/furnace/pcb2/

Download, for example, zone1.sch and view it with gschem. I used a
pair of comparators to detect the three states, and they drive mosfets
to replicate the state with the boosted current drive. They also do
voltage level shifting at the same time. The output is fed through a
shaper (the four passives) for managing impedance, i2c pullups, etc.

I think I ended up using 10k instead of 100k on the sense line,
though, for improved switching speed. You'll have to fiddle with all
that according to the speed you need.
.