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HALL OMNIDIRECTIONAL ENDSTOP - ONLY TWO COMPONENTS.

After looking at the current hall enstop options, I chose to make my own. I used the Honeywell SS451A. Advantages:

    1) Omnidirectional so you don't need to know magnet orientation.
    2) Its a switch; we have no need for ratiometric or linear data, we only need position.
    3) It can directly source 20ma - more than enough for most LED's.
    4) Through-hole package easy to work with (instead of SMD version).
    5) Supply voltage 3 to 24V
    6) No external capacitors are specified in the Honeywell installation datasheet.
    7) Cost = US$ 1.92/piece, I got 10 for US$ 11.87 or US$ 1.18/piece. 
       (DigiKey part number 480-3587-ND)

Disadvantages:

    1) No internal pull-up resistor, thus need an external resistor
        (You can turn on the pull-up resistor on the input RAMPS pin in Marlin or Sprinter).
    2  When turned on (magnet present) output is low. Magnetic field removed, output is high.
       (This can be compensated for in the software, or could add a PNP transistor to invert this, but it becomes much more complex).