Hall Effect Sensor

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Hall effect sensor.jpg


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.

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


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 Switch

The following circuit shows how a hall effect sensor can be used as a switch. The LED will light up when the sensor detects a change in the magnetic field.

Hall effect switch.jpg

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:

Ferrous sensor.jpg

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.

Ferrous sensor operation.jpg

Angle Sensing

By mounting a bipolar magnet on a shaft and placing a hall sensor near it, you can use the hall sensor to measure the angle of rotation of the shaft. The setup below was used in the "haptic paddle" project.


Connecting to the PC/104 Stack


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