Add ability to adjust fill trigger variable

[N3MIS15]

Using a potentiometer this change allows the trigger value for the beer fillers to be easily adjusted.

[lalo-uy]

The analog input read the votage provided by the pot and you use that value as threshold.

[franknh-design]

Hi folks,
I just finished building a beer filler. But I also wonder about the wiring diagram for variable trigger. Should positive wire that go to the rail somehow go through the potmeter?