Hall Effect Sensor

A Hall effect sensor varies its output in response to a change in magnetic field. They are primarily used for proximity sensing and position/rotation sensing. By placing a hall effect sensor near a magnet attached to your device that moves in some way, you can get a voltage proportional to the distance/orientation of the magnet. One commonly used configuration is placing the sensor directly above a dipole magnet attached to a rotating joint or shaft. The sensor (with some circuitry) will return an analog voltage proportional to the angle of the joint or shaft.

File:Hall effect sensor inside.png

How It Works

As you can tell from the name, the Hall Effect Sensor takes advantage of the phenomenon known as the Hall Effect. The Hall Effect refers to the potential difference (Hall voltage) on opposite sides of a thin sheet of conducting or semiconducting material through which an electric current is flowing, created by a magnetic field applied perpendicular to the Hall element. The equation associated with this is

$V=I\times B$

Circuitry

Honeywell makes a small hall effect sensor that can be mounted on a PCB board called the SS49. This device is used for analog sensing (angle, distance, etc.) A diagram of the circuit is shown below.

A company called iC-Haus makes another hall sensor chip that is intended for makeing angular measurements. The setup is shown in the diagram below:

Applications

A Switch

The following circuit shows how a hall effect sensor can be used as a switch.

Detecting a Nearby Ferrous Object

You can use a hall-effect sensor to detect a nearby metal object. An example of how to assembly such a sensor is shown below:

A small magnet is placed next to the hall effect sensor. Normally, the magnetic fields are uniform, but as a metal object approaches, they are scewed. The hall sensor picks up on this change and outputs a voltage.

References

• Wikipedia, "Hall Effect", http://en.wikipedia.org/wiki/Hall_effect
• Wikipedia, "Hall Effect Sensor", http://en.wikipedia.org/wiki/Hall_effect_sensor
• Honeywell, "Hall Effect Sensors", http://www.honeywell-sensor.com.cn/prodinfo/magnetic_position/technical/chapter2.pdf
• iC-Haus, "iC-MA", http://www.ichaus.com/upload/pdf/Ma_a2es.pdf
• Quasdorf, Joachim, "A Case Study: MR vs. Hall Effect for Position Sensing," http://www.sensorsmag.com/sensors/article/articleDetail.jsp?id=314520, Nov., 2005.