18 ms·

Common Hall-effect sensor myths (2022)

98 points by zdw 4y ago

pedrovhb 4y ago
Hall effect sensors are really neat. I'm a mechatronics engineer by education, but I almost exclusively work with software. One of the reasons for this is that I dislike the fallibility of The Real World™. Switches wear out with time, you get noise in your circuits if someone turns on the microwave, and all that - I click better with solving problems in the domain of ideas, and software is closer to that. On one hardware project I did a couple of years ago, which involved automated closing and opening of a sliding door, we used hall effect instead of mechanical for the limit switches. I didn't react strongly to the idea at the time but boy, was it a good one. No issues with aligning switches precisely, no worrying about switches wearing out or getting stuck, minimal handling of debouncing necessary. And it was even totally silent! I think this was the closest I got to perceiving something in the real world to be as elegant and consistent as (most) things are in the code world.
- runnerup 4y ago
  Hahaha whereas Hall effect sensors caused me no end of trouble using it as a design component to measure the current draw of an AC motor in a valve actuator. The EMF from the motor played all kinds of havoc on the Hall effect sensor.
- defrost 4y ago
  If you enjoyed triggering against events in the milliTesla range [1] imagine the excitement of continously measuring nine inputs in the nanoTesla range [2] - three axis magnetometers at the wingtips and tailboom of a drafting airframe [3] 80m above ground for millions of line kms per survey [4]. [1] https://www.ti.com/product/TMAG5124 https://www.ti.com/product/TMAG5124 [2] https://georesults.com.au/product/geometrics-g-822a-caesium-cs-vapour-magnetometer/ https://georesults.com.au/product/geometrics-g-822a-caesium-... [3] https://scintrexltd.com/wp-content/uploads/2017/02/CS-VL-Manual-773701-Rev0.pdf https://scintrexltd.com/wp-content/uploads/2017/02/CS-VL-Man... [4] https://www.youtube.com/watch?v=AZyNIGFHsE4 https://www.youtube.com/watch?v=AZyNIGFHsE4
- fest 4y ago
  There is another type of switch even more common in industrial automation: inductive switch, where the trigger mechanism relies on inductive coupling between an external target and a coil in sensor (for all practical purposes the target is ferrous metal- they do usually work against aluminum alloys or stainless steel but at greatly reduced range). I usually see hall-based switches being used to detect pneumatic cylinder position- the plunger in cylinders has an embedded magnet and there is a rail on the outside of cylinder where you can fix a small sensor.
- FpUser 4y ago
  Reed switch for this application might be even better
Veliladon 4y ago
I will die on the hill that hall effect control sticks and triggers are superior to pots. SEGA used them on the Saturn and Dreamcast controller sticks and triggers and they were awesome. It's good to see Gulikit making OEM stick parts and OEMs like NYXI putting them into products like the Wizard.
- nomel 4y ago
  For the game controller context, anyone who thinks otherwise has probably never taken apart an old potentiometer, and looked inside at the carnage. Things scraping together, wearing each other away, until they fail in a non graceful way. Solid state analog is hard to beat, in low current devices, with human speed dB/dt.
  - raverbashing 4y ago
    Hah you don't even need to take one apart Just get an old radio, fiddle with the volume control and hear the scratching
- Waterluvian 4y ago
  Okay I have almost zero hardware chops but this sings to me. Does that mean that the sensor is all solid state and the only moving bit is just a gimbal-like thingy attached to the rubber thumb interface to move a little magnet around? That’s got to be ridiculously simple and long-lasting. Or even trivial to make replaceable without having to replace any of the electronics.
  - p_l 4y ago
    That was literally why the infamous hall effect keyboard switches of Honeywell were designed. Keyboard were required to be very robust, and switches that required direct interaction were found lacking in reliability. Thus no-touch, special integrated circuit per key, hall effect keyboards were born before the advent of cheapness and higher reliabilty of mechanical switches drove them out due to price difference.
anonymousiam 4y ago
I didn't know much about Hall-effect sensors until I built a solar M&C system (in 2003) and I wanted to accurately measure currents (into/out of battery, out from solar array, and out of auxiliary charger). I didn't want to use shunt resistors because of losses, dealing with voltage offsets, and calibration uncertainty. I ended up using some metrology-grade Closed Loop Hall Effect Current Sensors (F.W. Bell CLN-200). Hall-effect sensors by themselves are pretty poor for this application, but these sensors consist of a traditional (AC type) current transformer, but instead of a closed core, there's a Hall-effect sensor placed in a small gap in the core loop. Instead of measuring current from the transformer windings, the windings are fed from an op-amp current source with feedback from the Hall-effect sensor with the result that the magnetic field produced by the transformer windings exactly cancels the magnetic field produced from the current flowing through the source cable. The current in the cable is thus known because it equals the product of the CT current and the turns ratio (in this case 200/1). The Hall-effect sensor here is only sensing the presence or absence of a magnetic field, and the CT is driven to null the field, so the system calibration is simple. (There's no need for any temperature compensation of the Hall-effect sensor.) Also, IIRC, these sensors have a pretty high operational bandwidth (DC to ~200kHz).
- gfaregan 4y ago
  Do you have any references or diagrams for the system?
- Animats 4y ago
  That's how clamp-around DC ammeters work. It's amazing that's even possible.
  - ilyt 4y ago
    But those require constant zeroing
    - xxs 4y ago
      since the device (clamp/fork meter) doesn't know if there is a current going or not... but if you control the load/current - it should be trivial to zero 'em.
prpl 4y ago
also why my 1997 Jeep Cherokee was running funny and a proper PITA to fix
- autotech 4y ago
  Those are particularly prone to failure on 4.0 (as you are now know) make sure you use an OE crank sensor.
FatActor 4y ago
#1 is weird. I would never look at a bipolar sensor with a wide hysteresis and think "latch", but after re-reading it that's totally what it is and makes me rethink my idea of a latch. And here I just thought they were for non-intrusively measuring current.
sakras 4y ago
I used a Hall Effect sensor on my robotics team and it caused nothing but issues. We were using it to PID our motors to be the same speed. I think there might’ve been some kind of interference from the motors, but I’m not sure. We ended up switching to an optical rotary encoder and all of our problems went away. Given my bad experience, reading that they’re so popular really surprised me. Are they actually finicky or did my team just do something wrong?
- marcosdumay 4y ago
  They seem to work incredibly well when everything is made of plastic, and incredibly badly when everything is made of steel. What is quite reasonable. If you go to a gym, try to keep track of your exercise counts and compare them to the machine counters. The machines almost never get them right. But for keyboards they seem to be pretty great.
- retSava 4y ago
  Halls depends on magnetic fields. Motors generate magnetic fields to a large degree, hence electromagnetic interference handling becomes important in those applications.
- fest 4y ago
  Many brushless motors (fans, electric scooters) have digital output (i.e. on/off) hall sensors triggered by motor magnets to read a coarse motor's shaft (to know which coil should be energized). There is even a higher resolution approach of using two or three analog output hall sensors sensing motor magnets to read fine stator position (for example, gimbal motors for DJI drones use this technique). Then there are ICs that contain several hall sensors that are arranged to measure absolute angle of diametrically magnetized target (these are the one's used in hall effect potentiometers, and I've seen them used for position feedback in brushless motor control). So, most likely your project had an issue with sensor placement, or the sensor wasn't correctly selected for the application They are no more finicky than IR sensors reacting to sunlight, or just about every type of sensor *also* being a temperature sensor: you have to be aware of what exactly is the sensor measuring and how the environment may affect it's measurements.
julian_sark 4y ago
Myth #6: Mixing SI and imperial units makes for good reading. How many millimeters are three inch again?
- xxs 4y ago
  76.2 - still puzzles me, though. While I can convert units in my my head, I have never used anything but metric... so I always convert them. The most common misuse is likely to be attributed to Canadian folks, I guess.
EtienneK 4y ago
I expect to see an explosion of hall-effect switches in gaming keyboards in the next few years following the success [1][2] of the Wooting 60HE [3] and the Steel Series Apex Pro [4] keyboards. [1] https://www.youtube.com/watch?v=2kvmccinWMk https://www.youtube.com/watch?v=2kvmccinWMk [2] https://www.youtube.com/watch?v=dUZxW2VzyIk https://www.youtube.com/watch?v=dUZxW2VzyIk [3] https://next.wooting.io/wooting-60he https://next.wooting.io/wooting-60he [4] https://steelseries.com/gaming-keyboards/apex-pro https://steelseries.com/gaming-keyboards/apex-pro
- simplyinfinity 4y ago
  I love my apex pro TKL Keyboard! The switches are a part of it, but the overall build and quality are amazing. I highly recommend it!
- lsaferite 4y ago
  I bought the Wooting Lekker keyboard and while the hall-effect switches are awesome, I realized afterwards that I've come to love low-profile mechanical keyboards too much to go back. If they release a low-profile version of the switches I'll gladly change over.
eternityforest 4y ago
Analog hall sensors are amazing. With a bit of filtering you make your activation point any arbitrary distance, and do hysteresis, and have a bit of flexibility to reconfigure if you decide you want to mount the magnet farther away.
hoseja 4y ago
>There are also those who believe that Hall-effect sensors don’t have a good range for practical use because magnetic fields decay exponentially over distance. That would be because they decay quadratically over distance...
- kragen 4y ago
  i think it's actually cubic, but 'exponential' is still wrong

98 points by zdw 4y ago

Hall effect sensors are really neat. I'm a mechatronics engineer by education, but I almost exclusively work with software. One of the reasons for this is that I dislike the fallibility of The Real World™. Switches wear out with time, you get noise in your circuits if someone turns on the microwave, and all that - I click better with solving problems in the domain of ideas, and software is closer to that. On one hardware project I did a couple of years ago, which involved automated closing and opening of a sliding door, we used hall effect instead of mechanical for the limit switches. I didn't react strongly to the idea at the time but boy, was it a good one. No issues with aligning switches precisely, no worrying about switches wearing out or getting stuck, minimal handling of debouncing necessary. And it was even totally silent! I think this was the closest I got to perceiving something in the real world to be as elegant and consistent as (most) things are in the code world.

runnerup 4y ago
Hahaha whereas Hall effect sensors caused me no end of trouble using it as a design component to measure the current draw of an AC motor in a valve actuator. The EMF from the motor played all kinds of havoc on the Hall effect sensor.
defrost 4y ago
If you enjoyed triggering against events in the milliTesla range [1] imagine the excitement of continously measuring nine inputs in the nanoTesla range [2] - three axis magnetometers at the wingtips and tailboom of a drafting airframe [3] 80m above ground for millions of line kms per survey [4]. [1] https://www.ti.com/product/TMAG5124 https://www.ti.com/product/TMAG5124 [2] https://georesults.com.au/product/geometrics-g-822a-caesium-cs-vapour-magnetometer/ https://georesults.com.au/product/geometrics-g-822a-caesium-... [3] https://scintrexltd.com/wp-content/uploads/2017/02/CS-VL-Manual-773701-Rev0.pdf https://scintrexltd.com/wp-content/uploads/2017/02/CS-VL-Man... [4] https://www.youtube.com/watch?v=AZyNIGFHsE4 https://www.youtube.com/watch?v=AZyNIGFHsE4
fest 4y ago
There is another type of switch even more common in industrial automation: inductive switch, where the trigger mechanism relies on inductive coupling between an external target and a coil in sensor (for all practical purposes the target is ferrous metal- they do usually work against aluminum alloys or stainless steel but at greatly reduced range). I usually see hall-based switches being used to detect pneumatic cylinder position- the plunger in cylinders has an embedded magnet and there is a rail on the outside of cylinder where you can fix a small sensor.
FpUser 4y ago
Reed switch for this application might be even better

Veliladon 4y ago

I will die on the hill that hall effect control sticks and triggers are superior to pots. SEGA used them on the Saturn and Dreamcast controller sticks and triggers and they were awesome. It's good to see Gulikit making OEM stick parts and OEMs like NYXI putting them into products like the Wizard.

nomel 4y ago
For the game controller context, anyone who thinks otherwise has probably never taken apart an old potentiometer, and looked inside at the carnage. Things scraping together, wearing each other away, until they fail in a non graceful way. Solid state analog is hard to beat, in low current devices, with human speed dB/dt.
- raverbashing 4y ago
  Hah you don't even need to take one apart Just get an old radio, fiddle with the volume control and hear the scratching
Waterluvian 4y ago
Okay I have almost zero hardware chops but this sings to me. Does that mean that the sensor is all solid state and the only moving bit is just a gimbal-like thingy attached to the rubber thumb interface to move a little magnet around? That’s got to be ridiculously simple and long-lasting. Or even trivial to make replaceable without having to replace any of the electronics.
- p_l 4y ago
  That was literally why the infamous hall effect keyboard switches of Honeywell were designed. Keyboard were required to be very robust, and switches that required direct interaction were found lacking in reliability. Thus no-touch, special integrated circuit per key, hall effect keyboards were born before the advent of cheapness and higher reliabilty of mechanical switches drove them out due to price difference.

anonymousiam 4y ago

I didn't know much about Hall-effect sensors until I built a solar M&C system (in 2003) and I wanted to accurately measure currents (into/out of battery, out from solar array, and out of auxiliary charger). I didn't want to use shunt resistors because of losses, dealing with voltage offsets, and calibration uncertainty. I ended up using some metrology-grade Closed Loop Hall Effect Current Sensors (F.W. Bell CLN-200). Hall-effect sensors by themselves are pretty poor for this application, but these sensors consist of a traditional (AC type) current transformer, but instead of a closed core, there's a Hall-effect sensor placed in a small gap in the core loop. Instead of measuring current from the transformer windings, the windings are fed from an op-amp current source with feedback from the Hall-effect sensor with the result that the magnetic field produced by the transformer windings exactly cancels the magnetic field produced from the current flowing through the source cable. The current in the cable is thus known because it equals the product of the CT current and the turns ratio (in this case 200/1). The Hall-effect sensor here is only sensing the presence or absence of a magnetic field, and the CT is driven to null the field, so the system calibration is simple. (There's no need for any temperature compensation of the Hall-effect sensor.) Also, IIRC, these sensors have a pretty high operational bandwidth (DC to ~200kHz).

gfaregan 4y ago
Do you have any references or diagrams for the system?
Animats 4y ago
That's how clamp-around DC ammeters work. It's amazing that's even possible.
- ilyt 4y ago
  But those require constant zeroing
  - xxs 4y ago
    since the device (clamp/fork meter) doesn't know if there is a current going or not... but if you control the load/current - it should be trivial to zero 'em.

prpl 4y ago

also why my 1997 Jeep Cherokee was running funny and a proper PITA to fix

autotech 4y ago
Those are particularly prone to failure on 4.0 (as you are now know) make sure you use an OE crank sensor.

FatActor 4y ago

#1 is weird. I would never look at a bipolar sensor with a wide hysteresis and think "latch", but after re-reading it that's totally what it is and makes me rethink my idea of a latch. And here I just thought they were for non-intrusively measuring current.

sakras 4y ago

I used a Hall Effect sensor on my robotics team and it caused nothing but issues. We were using it to PID our motors to be the same speed. I think there might’ve been some kind of interference from the motors, but I’m not sure. We ended up switching to an optical rotary encoder and all of our problems went away. Given my bad experience, reading that they’re so popular really surprised me. Are they actually finicky or did my team just do something wrong?

marcosdumay 4y ago
They seem to work incredibly well when everything is made of plastic, and incredibly badly when everything is made of steel. What is quite reasonable. If you go to a gym, try to keep track of your exercise counts and compare them to the machine counters. The machines almost never get them right. But for keyboards they seem to be pretty great.
retSava 4y ago
Halls depends on magnetic fields. Motors generate magnetic fields to a large degree, hence electromagnetic interference handling becomes important in those applications.
fest 4y ago
Many brushless motors (fans, electric scooters) have digital output (i.e. on/off) hall sensors triggered by motor magnets to read a coarse motor's shaft (to know which coil should be energized). There is even a higher resolution approach of using two or three analog output hall sensors sensing motor magnets to read fine stator position (for example, gimbal motors for DJI drones use this technique). Then there are ICs that contain several hall sensors that are arranged to measure absolute angle of diametrically magnetized target (these are the one's used in hall effect potentiometers, and I've seen them used for position feedback in brushless motor control). So, most likely your project had an issue with sensor placement, or the sensor wasn't correctly selected for the application They are no more finicky than IR sensors reacting to sunlight, or just about every type of sensor *also* being a temperature sensor: you have to be aware of what exactly is the sensor measuring and how the environment may affect it's measurements.

julian_sark 4y ago

Myth #6: Mixing SI and imperial units makes for good reading. How many millimeters are three inch again?

xxs 4y ago
76.2 - still puzzles me, though. While I can convert units in my my head, I have never used anything but metric... so I always convert them. The most common misuse is likely to be attributed to Canadian folks, I guess.

EtienneK 4y ago

I expect to see an explosion of hall-effect switches in gaming keyboards in the next few years following the success [1][2] of the Wooting 60HE [3] and the Steel Series Apex Pro [4] keyboards. [1] https://www.youtube.com/watch?v=2kvmccinWMk https://www.youtube.com/watch?v=2kvmccinWMk [2] https://www.youtube.com/watch?v=dUZxW2VzyIk https://www.youtube.com/watch?v=dUZxW2VzyIk [3] https://next.wooting.io/wooting-60he https://next.wooting.io/wooting-60he [4] https://steelseries.com/gaming-keyboards/apex-pro https://steelseries.com/gaming-keyboards/apex-pro

simplyinfinity 4y ago
I love my apex pro TKL Keyboard! The switches are a part of it, but the overall build and quality are amazing. I highly recommend it!
lsaferite 4y ago
I bought the Wooting Lekker keyboard and while the hall-effect switches are awesome, I realized afterwards that I've come to love low-profile mechanical keyboards too much to go back. If they release a low-profile version of the switches I'll gladly change over.

eternityforest 4y ago

Analog hall sensors are amazing. With a bit of filtering you make your activation point any arbitrary distance, and do hysteresis, and have a bit of flexibility to reconfigure if you decide you want to mount the magnet farther away.

hoseja 4y ago

>There are also those who believe that Hall-effect sensors don’t have a good range for practical use because magnetic fields decay exponentially over distance. That would be because they decay quadratically over distance...

kragen 4y ago
i think it's actually cubic, but 'exponential' is still wrong