This describes a dual Hall effect proximity detector of use in aiding compliance with the 'Moving Part Rule'. The circuit schematic is here.
The TLE4964-6M Hall sensors are used, see data sheet here.
Other types of limit switch may be used, the advantages of this Hall sensor design being :
Two Hall sensors are fitted to the board. Motion of a moving part is connected to some magnet holder such that a small magnet (3mm dia, 4mm long, see it here) is moved between being directly above one at either limit of motion. With no magnet near, the sensor draws a tiny current, guaranteed < 2.5mA.
As described in the data sheet, the Hall sensor Q output switches to GND in presence of an in-spec magnetic field. This is used to power an LED, increasing current consumption as limited by supply voltage and series resistor values.
The 'Standard Interface' Input recognises currents < 3mA as '0', with currents > 9mA registering '1'. Hysteresis designed into the Hall sensor and the controller input stages provides for noise immunity, ensuring clean transition between states.