He built this set of no-contact limit switches using a hall effect sensor. The small black package sticking out past the end of the protoboard is the sensor. It is used to detect a magnetic field.

This custom linear Hall effect sensor is a perfect example of this. By way of backstory, [Nixieguy], aka [The Electronic Mercenary], offers up a relatable tale — in the market for suitable ...

Delft University's inverted pyramid Hall-effect sensor achieves improved sensitivity and offset reduction, enhancing ...