Modern day position sensing technology is incredibly reliable, low-cost, and simple to implement. What does it take? A 3-pin device and a small magnetic material!
Hall effect sensing is all around us:
- Brushless DC motors use it for commutation decisions.
- Industrial valves use it for position information and to measure fluid flow rate.
- Vehicles use it for engine timing, traction control, pedal position, doors, and more.
- Game controllers use it to sense triggers.
- Laptops use it to sense lid closure.
- Handlebar grips, joysticks, and dials use it to sense movement.
The underlying physics is fascinating, and fortunately you don’t need an advanced degree in electromagnetism to grasp it. Whenever current flows through a conductor and there’s a magnetic field in the perpendicular direction, a tiny voltage develops across the conductor in the 3rd perpendicular direction. That’s the Hall effect. The reason the voltage forms is, magnetic fields exert the Lorentz force on electrons moving in the current, causing them to build up on one side. That uneven distribution of electrons amounts to microvolts, and it must be amplified to be usable.
Analog Hall sensors
TI’s DRV5053 Analog Hall ICs have 3 pins: power, ground, and the output. When no external magnetic field is present, the output drives 1V. When magnetic field lines come from the bottom through the top of the package, the output linearly reduces toward 0V based on the perpendicular component of the magnetic flux density. That’s equivalent to bringing a south magnetic pole near the top of the device.
As you’d expect, bringing a north pole close increases the output voltage toward 2V. A microcontroller ADC can use this voltage to understand the object’s position and acceleration.
Within each Hall IC, there are actually 4 sensing elements. They’re used in parallel with a chopping technique that cancels DC offset.
Digital Hall sensors
TI’s digital Hall sensors use a predetermined magnetic threshold, and their open-drain output pulls low when it’s reached. The 3 device types are:
- DRV5013 Latch – when the output goes low it latches, and doesn’t return to high-z until the opposite magnetic polarity is applied.
2. DRV5023 Switch – the output is only low while the magnetic field is present.
3. DRV5033 Omnipolar Switch – the output is only low while the magnetic field is present, and both magnetic polarities are treated the same. One advantage is that product assembly can be easier if the magnet orientation is flexible.
What’s so great?
Simple = flexible: these 3-pin devices come in both surface-mount and through-hole packages. Common magnets are available in discrete form and on films, coatings, and adhesives. Keep in mind that the moving part that’s sensed can act to block the field between the Hall sensor and the magnet.
Low-cost: sensing solutions often add an insignificant amount to the system BOM cost.
Protected from the world: Hall sensors are easily embedded in sealed enclosures that protect the PCB from water, corrosion, and ESD.
Never wears out: solid-state sensing works the same after 10 years as it did on Day 1.
Temperature consistency: performance is nearly constant across -40°C to 125°C.
Do you have an interesting application for Hall sensors? Please share below in comments; we want to hear! Order a sample of the Hall sensor today.