Why Hall effect sensors used so rarely in human input devices (HID)? - Page 1
Forum section: electronics / general

author: hun_yeti
author_rank: Contributor
timestamp: February 01, 2019, 02:26:13 am
content: Why Hall effect sensors used so rarely in human input devices (HID)?The only two i know that (probably) user hall effect sensors:Thrustmaster t16000m - a joystick, only uses hall effect sensor for the x and y movement of the joystick, it also supports rotation of the stick, but that's handled with a potenciométer, it needed a contact cleaner after only 2 months of use (i own one), i'm not sure isn't a magnetic sensor used for thatHaken continuum - a very expensive musical instrumentI haven't had the chance to try one, they are super expensive, starting at $3390If you'd say, it's because magnetic fields can disturb the device, don't forget that we are using magnetic data store for the most part of the century.I'm planning to make a (commercial) device that would utilize hall effect sensors, but i'm wondering if there is some serious downside of using them, since so few devices use them.The use case i'm considering:Having input keys with a decent travel length, where can track their position with relatively low latency and at at least ~256hz update rate,Alternative solution i could utilized but ruled out:Mechanical potenciométer - not the cheapest option, and will degrade with using, fairly quickly in this use case.Optical solutions - i'm not sure if i would be able to get it manufactured in a sealed fashion and with time dust and dirt would compromise it's operation, this applies to both encoder and the Adomax Flaretech (wooting) switchesForce sensors - They are pretty expensive as i see, and would require fairly complicated mechanical setupSo after this options, Hall effect sensing looks like a very nice option.TI DRV5053 looks ideal for the job, at $0.3 at 1ku it's price is acceptable. The magnets required would cost less than $0.1 each.For the physical assembly a cherry mx style switch could be used, since the have an extruding shaft, the magnet could be mounted on the end of it.They are the most resistant to any external effect, unless you put a very strong magnet next to it, but even that could be detected in software and the user could be warned that it wont work correctly in the current situation.Adomax Flaretech sound nice, but they are not really time tested, they are not very well protected. These "switches" are basically just optical modulators, you need to have an LED and a light sensor on the pcb, the switch itself is really just a "mirror" that changes the amount of reflected light based on how much it is pressed.Am i missing someting? Please let me know!

author: amyk
author_rank: Super Contributor
timestamp: February 01, 2019, 03:26:39 am
content: The main reason is cost. Apparently you can find keyboards with hall-effect switches now, but they're still quite rare.

author: David Hess
author_rank: Super Contributor
timestamp: February 01, 2019, 03:55:36 am
content: Quote from: hun_yeti on February 01, 2019, 02:26:13 amHigh density magnetic storage relies on incredibly high field strength generated over microscopic distances. Typical handheld magnets will have no effect on modern magnetic storage but will completely disrupt an unshielded hall effect device.QuoteIn the past hall effect sensors had poor reliability but I am not sure about integrated hall effect sensors. They are not precision devices which matters in some applications.QuoteI would also consider reluctance (inductance with a moving core) sensors and capacitance sensors. In the past and even now in high reliability applications,LDVTsare still used but they are more complicated. I think LVDTs should be used instead of hall effect sensors in human safety applications like drive-by-wire vehicles.

author: Brumby
author_rank: Unknown
timestamp: February 01, 2019, 04:05:15 am
content: Quote from: David Hess on February 01, 2019, 03:55:36 amEver pulled the magnet out of the seek arm actuator of a 3.5" HDD? That is one serious bit of magnetic material, yet doesn't seem to be a problem for data integrity on the nearby disc.

author: Marco
author_rank: Super Contributor
timestamp: February 01, 2019, 05:08:27 am
content: You could do a rotational sensor (at the pivot point) based on capacitance between overlapping electrodes.Main problem I see with Hall effect sensor is cross talk.

author: hun_yeti
author_rank: Contributor
timestamp: February 01, 2019, 10:41:38 pm
content: Quote from: amyk on February 01, 2019, 03:26:39 amI heard about that, although it's a bit different since that is only an "on/off" button, while i need an analog readout.Quote from: David Hess on February 01, 2019, 03:55:36 amI'm not really worried about the precision of it, i only really need 8 bits out of it.Re-calibrating, even on the fly is not an issue and can be easily done, assuming that the amount of change, as the key travels does not change.Quote from: David Hess on February 01, 2019, 03:55:36 amReluctance sensors only sense a changing magnetic flux, processing it would be pretty heavy, especially compared to a hall effect sensor.LVDTs are nice but they are expensive, bulky and i don't have any human safety application.For some reason i did not think of capacitive sensing, so i'm going to investigate that.It's a bit funny because the keyboard i'm using every day for the last 3 years has capacitive buttons. Nevertheless topre capcitive switches construction are pretty involved and not easily done.Thanks for the suggestions!Quote from: Marco on February 01, 2019, 05:08:27 amI'm not really sure what kind of rotation sensor do you mean, but there are no pivot points, it's a linear up/down motion.Crosstalk is the least thing i worry about. I only need to detect ~3.5mm of up/down motion, while they are at least 18mm apart, the change in the position nerby magnet between fully pressed and released is 0.34mm, that's a 2% change, i can easily live with that.I only said magnetic storage, didn't say "modern HDD". I know they are obselate but floppy disks had pretty long lifespan. Also tapes can be erased with a magnet aswell.

author: MT
author_rank: Super Contributor
timestamp: February 01, 2019, 11:54:30 pm
content: As Hakken is an quite old design why not a Linnstrument which i personally think beats them all, unfortunately to a price, i recall its capacitive and/or resistive sensing.http://www.rogerlinndesign.com/linnstrument.htmlAlso there is Roli Seaboard. I wonder what kind of sensing they use since tangents/sensors seams to be gelly like!Also the competition is fierce for past 3-4 years in this area one can by quite chap general purpose capacitve surfacesin which the top is replaceable with whatever layout you want.Here just 2 examples.https://www.play-joue.com/en/https://sensel.com/

author: David Hess
author_rank: Super Contributor
timestamp: February 02, 2019, 12:01:02 am
content: Quote from: hun_yeti on February 01, 2019, 10:41:38 pmBoth reluctance and capacitance can be used in a simple oscillator and frequency is one of the easiest things for digital circuits to measure.

author: amyk
author_rank: Super Contributor
timestamp: February 02, 2019, 01:32:32 am
content: Quote from: David Hess on February 01, 2019, 03:55:36 amDo you have any evidence of that? They've been used in electronic engine ignition systems for decades, switching dozens to hundreds of times per second, and likewise in brushless fan motors. It's rare for them to fail.

author: timelessbeing
author_rank: Frequent Contributor
timestamp: February 02, 2019, 01:55:14 am
content: Quote from: hun_yeti on February 01, 2019, 02:26:13 amvideo game controllers use them

author: David Hess
author_rank: Super Contributor
timestamp: February 02, 2019, 01:58:26 am
content: Quote from: amyk on February 02, 2019, 01:32:32 amPersonal experience.QuoteThe engine ignition pickups I am familiar with are reluctance sensors. I have had plenty of non-integrated hall effect sensors in brushless motors fail.

author: hun_yeti
author_rank: Contributor
timestamp: February 02, 2019, 11:59:56 am
content: Quote from: timelessbeing on February 02, 2019, 01:55:14 amWow, i didn't even think of that really, and it seems that it's true for the last 20 year. I guess if it's good enough for Sony and Microsoft, it's good enough for me!Although that's not a lot of different products, just huge volume.Quote from: MT on February 01, 2019, 11:54:30 pmI really don't like the idea of these input devices.They have absolutely no feedback to the user, there's a reason why button grid controllers are more popular amoung musicians (among anyone who would need specialized keys) than touch controllers.I think an instrument needs to have some physical feedback, espeically when there is concrete notes, just a range. Any string instrument have tons of physical feedback to the player.This is really far from what i want to achieve anyway. I just want to have buttons that have an analog input range, that can be read at any time.Quote from: David Hess on February 02, 2019, 12:01:02 amFor reluctance, i think that would require to have connected component on the moving part. I'd like to avoid that, since that's something that's very hard to do in a a relaibly way.Capacitance sensing might work tough.

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 02, 2019, 12:07:29 pm
content: IIRC, there were several (many?) keyboard designs that used Hall-effect in each key.I don't think the initial premise of the question is correct.

author: hun_yeti
author_rank: Contributor
timestamp: February 02, 2019, 04:23:05 pm
content: Quote from: Richard Crowley on February 02, 2019, 12:07:29 pmCare to show a few examples? The german RAFI company did manufacture some a long time ago, at an extraordinary price, but they don't seem to do that anymore.Recently there was a keyboard buy on massdrop, for a hall effect keyboard, where the overall rating for it is under 1.5 stars out of the 5.Even if there are a few, they are incredibly rare, especially compared to how many rubber membrane, mechanical switches or even optical switches there are.

author: MT
author_rank: Super Contributor
timestamp: February 02, 2019, 05:02:04 pm
content: Quote from: hun_yeti on February 02, 2019, 11:59:56 amReally!? yet you seams be for capacitive sensing who is the worst of them all, but i would like to see poly Theremin interface for sure.I havent studied Hakken in detail but it seams the only feedback it gives is sponginess, Roli seaboard could be said to be the same as Hakken also giving back a sponginess/clayess kind of feedback but i cant see any particular muscular or motorik, vibrationall (mobilephone, personal pager, massage stave) feedback in either one.QuoteI assume you meant non touch responsive buttons, then i disagree since most musicians go for multi directional touch sensitive interface silicone button , branch MI sales figures points to that. Point are, you can bild anything with any features there are but the first thing a musicians will complain about is the asking price, as have been shown time and again.QuoteWell peoples milage vary, piano (string hammer) players little of tactile feedback at all while church organists(standing wave in tube) have lots of vibration feedback despite players contact only interface.Quoteyou want both feedback and non feedback?!, well then its classic resistive foam/esd bags/conductive rubber sheets cut into size.

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 02, 2019, 05:49:43 pm
content: Quote from: hun_yeti on February 02, 2019, 04:23:05 pmQuoting from your very citation:QuoteYou said "used so rare" and your citation says "popular in keyboards". So you can understand my confusion.Quote

author: hun_yeti
author_rank: Contributor
timestamp: February 02, 2019, 07:01:06 pm
content: Even if all the nuclear power plants, aircraft cockpits used hall effect buttons, that's pretty still extremely rare. But obliviously not every one of them used hall effect switches, and it appears that they don't do it anymore since you can't really buy an industrial hall effect keyboard or keys, most references to it trace back to the 80's.Also, compared to the number of other input devices, that amount is marginal at best.

author: hun_yeti
author_rank: Contributor
timestamp: February 02, 2019, 07:18:11 pm
content: Quote from: MT on February 02, 2019, 05:02:04 pmI mean capacitive sensing of a buttons linear position, not sensing touch, that's completely different use case.QuoteFeedback doesn't have to be 'real', but you need to be able to feel it. Touching down harder on a capacitive surface does not offer feedback, you can't build muscle memory for that, while you can easily learn press an organ's key partially and since it has enough travel you can learn it to control easier.QuoteI have no idea what are you saying hereQuoteI'd argue that the piano key offers a lot of feedback to the players. Playing a real piano feels way more connected than playing on a cheap midi keyboard.I want feedback, although that's might be the wrong word for it.I want it to have a feel.A smooth, flat surface has absolutely no feel, while, for example, a piano key does. The point is that the user should have an easier association of what's happening in the sound, for what physical motion.The resistive foam type of sensor would probably die after a few hours of use.

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 02, 2019, 08:05:24 pm
content: I used many ordinary QWERTY hall effect keyboards in ordinary office and computer room settings. Never been in a nuclear plant, etc. But then perhaps I am older than you and have first-hand experience of the era.Certainly the reason they are not seen anymore is because new technology allowed simpler, better and cheaper alternative ways of making keyboard switches, so like many technologies Hall-effect was made essentially obsolete by progress.

author: Marco
author_rank: Super Contributor
timestamp: February 03, 2019, 09:37:00 am
content: Quote from: hun_yeti on February 01, 2019, 10:41:38 pmThis kindof sensor.Why would you want do a pure linear motion? You need lots of rigidity and tight tolerances to make a large key move evenly up and down regardless of where you strike it. A hinged key such as a piano key is easier in that respect and allows you to measure rotation rather than distance.

author: SilverSolder
author_rank: Super Contributor
timestamp: February 03, 2019, 03:59:23 pm
content: You can get some pretty cool hall effect products these days, for example Rotary Position Sensors:https://ams.com/as5132Pretty mind blowing alternative to an optical rotary encoder!

author: hun_yeti
author_rank: Contributor
timestamp: February 03, 2019, 05:42:35 pm
content: Quote from: Marco on February 03, 2019, 09:37:00 amI want to use cheap, and widely available cherry mx style switches, the shaft extrudes from the housing when the button is pushed down, so i'll just stick a tiny magnet on the end of the shaft.I want it to be compact, at least for the first version.I like the hinged design, and it it can have a better feel as well, but they required way more space, and the need to be stacked on each other if more rows are desired, while plain linear switches can have multiple rows while laying flat.That kind of sensor sounds really nice to use instead of optical encoders.Quote from: SilverSolder on February 03, 2019, 03:59:23 pmcool, but at $4 1ku price they are defiantly not a way to lower your bom cost.If i'd need to do something like that i'd use 3 cheaper sensors. If i wanted to have a digital output, it's just ad a cheap PIC mcu or something, it would still be less than third the price.