About Hall effect sensors
The Lorentz Force
When a charged particle (e.g. electron) moves through a magnetic field, it experiences a force perpendicular to its traveling velocity and the magnetic field direction. This force is known as the Lorentz force.
The Lorentz force is described by the following relation:
F = q(v x B)
Where q is the charge of the particle, v is the electron velocity, B is the magnetic field, and F is the resulting force felt by the electron under the influence of a magnetic field.
The Hall effect
As an electric current flows through a conducting material in the presence of a magnetic field, the magnetic field induces the Lorentz force upon the moving electrons.
This deflection of electrons results in the accumulation of electrons on one side of the conductor, thereby inducing a potential difference between both sides of the conductor. This potential difference can be measured and is known as the Hall voltage.
Hall effect sensors
A Hall effect sensor incorporates the concepts of the Hall effect and the Lorentz force.
Commercial Hall effect sensors
Hall effect sensors usually come in two forms commercially, as an independent Hall effect sensor, or integrated onto a module (e.g. SEN080604 and 44E).
Hall effect sensors that are integrated into a module often come equipped with a tiny bulb to indicate the presence of a current flow. Let us check this out on the 44E sensors using a conventional bar magnet The power (red) and ground (black) are connected up. There is no use for a microcontroller for this test other than to provide a power supply.
When there is no magnetic field near the sensor, the built-in bulb does not light up.
When the North pole of the bar magnet is brought close to the back of the Hall sensor, the built-in bulb lights up. Thereby confirming the presence and polarity of the magnetic field. When the South pole of the bar magnet is brought close to the back of the Hall sensor, the built-in bulb does not light up.
Likewise, bringing the North pole of the bar magnet close to the front of the Hall sensor does not result in the built-in bulb lighting up, whereas bringing the South pole of the bar magnet lights up the built-in bulb.
Applications of Hall effect sensors
Hall effect sensors have a variety of applications. They can be made into switches and integrated into security systems. They can also be used to detect position, velocity, and rpm by sensing magnetic field, voltage, and current changes. Their non-contact characteristic makes them versatile and reliable.
As the Hall effect is a consequence of an externally applied magnetic field, the strength and direction of the applied magnetic field can be detected by a 3-axis Hall sensor, often known as a 3-axis magnetometer or digital compass sensor.
Such modules can be found commercially as well, e.g. HMC5883L/QMC5883L Compass Sensor (3-axis) and are often used in geomagnetism measurements. In fact, it provides a cost effective position sensing module for gaming controller joysticks and even the GPS in your mobile phones.
Automotive systems and magnetic switches
Hall effect sensors are often found in cars for various uses. For instance, the safety feature of modern cars alerts the drivers of passengers who have yet to strap in. A Hall effect sensor within the seat belt buckle is activated when the seat belt latch pushes a magnet towards the Hall effect sensor. This induces a Hall voltage which will be detected.
A common application of Hall effect sensors can be found in the rotating parts, such as cooling fans equipped in computers.
Please note that by dismantling such fans, you will risk permanently damaging it. We advise against doing so unless you have a fan which you wish to discard.
Removing the blades from its frame reveals the components which help the fan rotate. For instance, there are the obvious coils of wire which are electromagnets.
Below the coils lie the integrated circuit which controls the coils to facilitate the rotation of the fan. Within the integrated circuit lies the Hall sensor which is tasked to detect the generated magnetic field and to keep the fan on constant rotation.
After considering these everyday applications of Hall effect sensors around us, it is your turn to come up with a fun device to demonstrate the Hall effect sensor!