Learn the Basics of Sensors
A series of articles about magnetic sensors. This includes Hall-effect, GMR, TMR, and reed switches.
Introductory Articles about Magnetic Sensors
In order to use magnetic sensors, you must properly position and orient bar magnets near the sensor. In order to do this correctly, you must understand how a sensor responds to magnetics fields. By knowing the shape of a bar magnet's field, you can easily determine how to operate a sensor with a bar magnet.
Tunneling Magnetoresistance (TMR) Switches are polarity sensitive devices that respond to a magnetic field. A correctly oriented magnet will turn them on and off.
A reed switch consists of two ferrous leads sealed inside a glass tube. With an appropriate magnetic field applied, the leads will attract each other and snap together.
A Giant Magnetoresistive (GMR) switch turns on when a magnet is brought near. It is not polarity sensitive. When a magnet in the correct orientation approaches, the GMR switch will activate.
Bipolar switches are similar to latches. They activate with one pole and then deactivate with the opposite pole. Unlike a latch, the response to south and north pole is probably not symmetric. A particular device might respond more to one pole than the other.
An omnipolar switch is like a unipolar switch except that it responds to either magnet pole. As either pole of a magnet nears the switch, it will activate.
A Hall-effect latch is a device that is activated by one pole of a magnet and deactivated by the other. In many types of latches, the south pole activate the latch and the north pole deactivates. Once the latch has been activated or deactivated, it stays in the same electrical state until the other magnet pole is brought near.
A unipolar switch is a device that responds to a magnetic field. When the correct pole of a magnet is brought near, it turns on. When the magnet is moved away, it turns off. The actual details are more complicated, but this is the basic idea.