For the limit switches on a custom 3D printer I’m designing, I want to try out some contactless sensors. I have chosen to use hall effect sensors, which are sensitive to a magnetic field.There are three different types of these sensors available. First, there’s the omnipolar hall sensor, which turns on when a magnet comes in its vicinity. Next is the unipolar one, which turns on as long as a specific magnetic pole is close enough, which pole depends on the sensor. Finally, there’s the bipolar hall effect sensor, which latches on when one pole comes close and only turns off when it senses the other pole.