I have a set up where I auger feed my hopper and thought about having it auto fill.
but the fact that when the hopper needs filling the ash pan needs emptying.
So what I do is when I go down to empty the ash pan, I switch on the hopper feed auger and by the time I finish with the ashes,
the hopper is full and I turn off the auger feeding the hopper.
I figured as dirty and corrosive as coal is, any auto fill would eventually fail and I would have a mess.
I did make up a simple way to know when the hopper is empty and ash pan is full, it has been working well for 2 years.
I'll post it below ( I also believe in the KISS method ) build a hopper empty/ash pan full indicator ....cheap