[HN Gopher] TrackWeight: Turn your MacBook's trackpad into a dig...
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TrackWeight: Turn your MacBook's trackpad into a digital weighing
scale
Author : wtcactus
Score : 425 points
Date : 2025-07-21 14:51 UTC (8 hours ago)
(HTM) web link (github.com)
(TXT) w3m dump (github.com)
| benoau wrote:
| There used to be iPhone apps that did something similar -
|
| https://www.theverge.com/2015/10/28/9625340/iphone-6s-gravit...
| ashertrockman wrote:
| If anyone happens to be using an iPhone 6S...
| http://touchscale.co/
| hackmiester wrote:
| This worked all the way up through the iPhone Xs.
| jmb99 wrote:
| The single most irritating killed feature from Apple.
| Redesign half of their UI to rely on 3D Touch to make
| sense, then get rid of 3D Touch without redesigning the UI.
| Previewing links, moving the cursor, interacting with
| items, they're all "press and hold until haptic feedback"
| instead of "quickly press hard and get immediate feedback."
| Easier to accidentally trigger, slower to trigger on
| purpose.
| 05 wrote:
| Hardware cost+extra weight (need to make the glass
| thicker to be able to handle extra force and not push on
| the display). Turns out nobody was really using it
| because discoverability sucked..
| jmb99 wrote:
| Hardware cost & weight, fine. Glass doesn't need to be
| thicker than it currently is (I can press on my 13 Pro's
| screen about twice as hard as was needed for 3D Touch's
| max depth, and no issues with the screen), and the last
| time I replaced a battery on a 12, the screen was just as
| thick as the XS.
|
| >Turns out nobody was really using it because
| discoverability sucked..
|
| Sure, but then redesign the UI after removing 3D Touch to
| not be equally undiscoverable but less precise. Even on
| the latest iOS beta with its full redesign, there's still
| many, many actions that require a long press that are
| completely undiscoverable. (For example, if you don't
| have the Shazam app installed, go find the list of songs
| Siri has recognized when asked "What's this song?" Don't
| look up the answer.)
| echoangle wrote:
| > Glass doesn't need to be thicker than it currently is
| (I can press on my 13 Pro's screen about twice as hard as
| was needed for 3D Touch's max depth, and no issues with
| the screen)
|
| I dont think this is a great argument. The glass maybe
| needs to be thicker so the sensors on the border can
| properly measure the pressure, not because the screen is
| close to shattering.
| sejje wrote:
| Maybe you had a hard time parsing his comment.
|
| He is capable of pressing twice as hard as the feature
| required at maximum. The screen handles 2x the maximum
| without issues. Therefore, the glass is thick enough to
| handle half that pressure,as required by the feature.
|
| It's a good argument.
| echoangle wrote:
| As far as I know, the pressure is measured around the
| edge of the screen. If the screen is thin enough, it
| could bend when pressed and the pressure applied to the
| center of the screen can't be properly measured. I don't
| think the problem with a too thin screen is the screen
| breaking when pressing it.
| cluckindan wrote:
| Nobody? Really? It's definitely the UX feature I miss
| most on modern iPhones. Long press feels janky in
| comparison.
| gxs wrote:
| Really? For me it's the "open image in new tab" option in
| safari
|
| Have no idea why you'd go out of your way to do that
| other than placating image sharing services
| yoz-y wrote:
| The discoverability sucked because Apple never rolled
| this out to all of the devices, themselves grossly under
| utilized the feature and eventually ghosted it.
|
| It was by far the best cursor control paradigm on iOS.
| Now everything is long press which is slow and as error
| prone.
|
| I'm all for proposing different paradigms as
| accessibility but 3dtouch was awesome.
| macNchz wrote:
| 3D Touch was amazing for typing alone, I miss it
| basically every day when I type more than a couple of
| words on my phone. It was so great to be able to firm-
| press and slide to move the insertion point, or firm _er_
| press to select a word or create a selection. It was like
| a stripped down mobile version of the kind of write-and-
| edit flow of jumping around between words that I can get
| on a proper keyboard with Emacs keybindings drilled into
| my brain.
| bagels wrote:
| I hated when my mother in law came to me for help using
| her iPhone. She had a hard time controlling and
| understanding 3d touch.
| behnamoh wrote:
| I don't like it when old people are the reason the rest
| of us can't have nice things. Some grandma in Nebraska
| can't use 3D touch and now the rest of the demographic of
| Apple's customers are deprived of it.
| wat10000 wrote:
| There was a principle of UI design that all UI actions
| should be discoverable, either with a visible button or a
| menu item in the menus at the top of the screen (or
| window on Windows). This is annoying for power users and
| frequently used actions, so those can _also_ be made
| available with keyboard shortcuts or right-click actions
| or what have you, but they must always be optional. This
| allows power users to be power users without impacting
| usability for novices.
|
| We've been losing this idea recently, especially in
| mobile UIs where there's a lot of functionality, not much
| space to put it in, and no equivalent of the menu bar.
| nottorp wrote:
| When I had an iPhone XS i could never understand how to
| predictably do a normal touch or a 3d touch, or where
| exactly the OS has different actions for one vs the
| other.
|
| And I play games [1] using just my macbook pro's
| trackpad...
|
| [1] For example, Minecraft works perfectly without a
| mouse. So does Path of Exile. First person shooters ofc
| don't.
| notpushkin wrote:
| https://archive.li/KtfxO
| wanderingstan wrote:
| My memory was that the weight API was made private because they
| didn't want people using iPhones for drug deals.
| cryptoz wrote:
| You can use any phone with a barometer to make a scale. All
| iPhones since the 6, and all the Pixels, and Samsung flagships
| have one. You get a zip loc bag, blow some air into it, put
| your phone in running an app that shows the pressure in a big
| font (so you can see it through the ziploc). Then you put an
| object of known weight on it like a quarter (balanced carefully
| on top of the air-filled ziploc) and note the pressure change
| on the display. With that, I think the weight / pressure change
| scales linearly, so you can now weigh anything small that you
| can balance on the ziploc.
| jbverschoor wrote:
| Dropbox shouldn't exist either bc we have rsync ;)
| Nathan2055 wrote:
| The infamous Dropbox comment[0] actually didn't even cite
| rsync; it recommended getting a remote FTP account, using
| curlftpfs to mount it locally, and then using SVN or CVS to
| get versioning support.
|
| The double irony of that comment is that pretty much all of
| those technologies listed are obsolete now while Dropbox is
| still going strong: FTP has been mostly replaced with SFTP
| and rsync due to its lack of encryption and difficult to
| manage network architecture, direct mounting of remote
| hosts still happens but it's more typical in my experience
| to have local copies of everything that are then synced up
| with the remote host to provide redundancy, and CVS and SVN
| have been pretty much completely replaced with Git outside
| of some specialist and legacy use cases.
|
| The "evaluating new products" xkcd[1] is extremely
| relevant, as is the continued ultra-success of Apple:
| developing new technologies, and then turning around and
| marketing those technologies to people who aren't already
| in this field working on them are effectively two
| completely different business models.
|
| [0]: https://news.ycombinator.com/item?id=9224 [1]:
| https://xkcd.com/1497/
| kiddico wrote:
| I'm adding this to my list of obscure tools I have in the
| back of my head
| nemosaltat wrote:
| no affiliation whatsoever but the app PHYPHOX has access to
| basically all of your iPhone sensors and can show the
| information in real time and save it, even has the capability
| of running a local python server so you can access it from a
| web browser on the same network or tethered device.
| thomascountz wrote:
| I've use Sensor Logger[1], which does the same. I enjoy
| following its development.
|
| [1]: https://github.com/tszheichoi/awesome-sensor-logger
| xsmasher wrote:
| Wait, I know this one. You give the barometer to the
| superintendent if he tells you the height of the building.
| Raed667 wrote:
| how about stacking the barometers ?
| rzzzt wrote:
| Do I measure the passenger plane with or without the
| ship?
| ChrisMarshallNY wrote:
| Very cool, but I'd still probably just buy a cheap digital scale.
| raldi wrote:
| The best digital scale is the one you have with you ;)
| j45 wrote:
| One less thing to carry.
| ChrisMarshallNY wrote:
| I used to travel with one of these[0].
|
| [0] https://en.m.wikipedia.org/wiki/Macintosh_Portable
| tln wrote:
| No download link?
| ChrisMarshallNY wrote:
| I think it's a DIY project.
| addandsubtract wrote:
| DIY projects can't be downloaded?
| ChrisMarshallNY wrote:
| By "downloaded," I expect that you mean "Built, tested, and
| deployed." It's not an App Store app. It's basically a
| technology demo. Get Xcode, and build it and run it.
| lucasoshiro wrote:
| A .dmg or at least a CLI instruction would really help
| ChrisMarshallNY wrote:
| You could always request that from the author. Since it's
| a Mac app, they could do that. Not so, if it were an iOS
| app.
|
| It's a pretty basic SwiftUI app. They haven't really
| polished it, so I could see why they might not be
| interested in making it much more accessible. It's a tool
| for Mac geeks.
|
| Speaking for myself, I have a whole bunch of packages,
| and almost every one has a test harness. Many of the test
| harnesses are "full-fat" iOS apps, so they can't be
| provided as releases, unless I create an App Store app
| for each one.
|
| They need to be built and run. A couple are Mac apps, but
| the whole deal with them, is that they are _test
| harnesses_ , so divorcing them from the IDE is sort of
| negating their purpose. They are meant to help other
| Apple developers to understand and use the packages the
| apps are associated with.
| qwertytyyuu wrote:
| Ah I remember being able to do this with the iPhone 6s
| hn_throwaway_99 wrote:
| I think this is neat, but only in a Rube Goldberg machine sort of
| way. The instructions are:
|
| 1. Open the scale
|
| 2. Rest your finger on the trackpad
|
| 3. While mainting finger contact, put your object on the trackpad
|
| 4. Try and put as little pressure on the trackpad while still
| maintaining contact. This is the weight of your object
|
| That is, the pressure sensors only work if it detects
| capacitance, so you need to be touching the track pad (but not
| too much!!) _while_ weighing something.
| linux2647 wrote:
| Sometimes you can get capacitance to be detected if you hover
| your finger just millimeters over the trackpad
| whycome wrote:
| Can't you get capacitance with a wet sponge? Like your typical
| dish cellulose sponge. You could make a small platform?
| asimovDev wrote:
| I remember drawing on my old iPad back in the day by shoving
| a wet q-tip into a BIC pen and using it as a stylus. I am
| sure something similar could be rigged here
| dotancohen wrote:
| I've used carrots and cucumbers as a capacitive stylus
| while wearing gloves.
|
| It's the reason why I love Note and S Ultra phones - the
| stylus. I'm using it now.
| doubled112 wrote:
| The recipe was on your phone/tablet and there was no way
| you were taking your gloves off?
| dotancohen wrote:
| Nice. No, I preemptively armed myself with a carrot
| before taking the dog for a walk in cold weather.
|
| I only had a non-stylus smartphone for a year and a half
| before whimpering back to the Note series. It's what
| keeps me in the Samsung sphere of influence.
| mietek wrote:
| I used my nose.
| throwanem wrote:
| Ever try putting gloves back on when your hands and the
| gloves are both wet? This is why I print recipes on the
| laser, and just take the paper version downstairs.
| Y_Y wrote:
| I use this to avoid touching the stupid self-checkout
| machines when buying groceries
| namdnay wrote:
| Could a small piece of conductive foam or some cleverly layered
| tin foil+paper work? So put the object on the shim (which has a
| known or even negligeable weight)
| 83 wrote:
| Could probably make a small stand with nubbins from touch
| screen pens as the feet.
| svnt wrote:
| No, you need roughly a small human's worth of ground mass for
| most capacitive touch sensors to register a touch.
| bigyikes wrote:
| Tape a wire to the trackpad and hold the wire?
| stavros wrote:
| How do capacitive pens work?
| acct-litter-al wrote:
| I once put some aluminum duct tape completely over the touch
| pad of an old laptop to see what would happen. Turns out it
| induced enough "eddy currents" to make the mouse move around
| the screen without me touching it--in a way, visualizing the
| currents!
|
| I connected the foil to ground using a small strip of the
| tape to the ground metal of a USB port on the side and it
| disabled the touch pad.
| acct-litter-al wrote:
| Looking back, it would have been interesting to code up a
| program to record the movement of the mouse as a trail of
| pixels...
| ashertrockman wrote:
| On iPhones at least a hack was to rest a metal spoon on the
| screen and weigh something in the spoon...
| jihadjihad wrote:
| Could you accurately weigh a hot dog?
| dtgriscom wrote:
| No, only cool ones.
| wanderingstan wrote:
| This is a very clever hack, _exactly_ the sort of thing that
| belongs on Hacker News.
| pmxi wrote:
| This is clever! and potentially useful too.
|
| Have you done any testing to determine how precise and accurate
| this is? I suspect their must be a lot of variance between
| laptops, since this isn't an intended use case.
| mschuster91 wrote:
| > I suspect their must be a lot of variance between laptops,
| since this isn't an intended use case.
|
| Yeah and so it is for ordinary strain gauges aka load cells.
| You can either use a 2 point calibration (aka no load followed
| by known load) or if you want more precision a 3 point
| calibration.
|
| [1] https://en.wikipedia.org/wiki/Load_cell
| cluckindan wrote:
| I would assume Apple hardware comes precalibrated. Homogeneity
| is everything for their product lines, down to individual
| calibration of screens and audio hardware. It would be weird to
| get a new laptop and have its trackpad feel different.
| hbn wrote:
| They have a setting for adjusting the pressure needed to
| activate a click.
|
| I wonder if that affects this app at all.
| DonHopkins wrote:
| Just what I need to roll the quantitative doobie.
| qoez wrote:
| Apparantely on safari there's touch strength so this should be
| possible to make for the web too, cool
| ashertrockman wrote:
| Somebody could use this as a starting point.
| http://touchscale.co/ You'd have to collect new data on touch
| strength vs. weight to get the regression parameters.
|
| (If you do this, let me know and I can add it to the site
| above, and then we can both delight in the surprisingly large
| amount of unmonetizable traffic it gets.)
| thrownawaysz wrote:
| Can someone compile a binary? Don't want to download Xcode just
| for that...
| incanus77 wrote:
| This reminds me of how, twenty years ago, I used the PowerBook's
| hard drive vibration sensor to rig up a seismograph to measure
| construction noise:
|
| https://allthegooddomainsweretaken.justinmiller.io/2007/04/0...
| bitwize wrote:
| Reminds me of the people who used their ThinkPad's vibration
| sensor to detect smacks on the machine, and rigged their X
| window manager to switch virtual desktops when smacked from the
| appropriate side, panning right when smacked on the left, and
| left when smacked on the right.
| 1bpp wrote:
| this update breaks my case smacking workflow, please revert
| incanus77 wrote:
| Oh, I vaguely remember someone hacking that for some sort of
| windowing back then on OS X!
| akubera wrote:
| The smackbook pro!
| https://www.youtube.com/watch?v=6uvQTTPr9Rw
| BolexNOLA wrote:
| What a great name
| incanus77 wrote:
| That's it exactly. I clearly remember the nonchalantness.
| stockresearcher wrote:
| I heard that IBM decided to move out of this building [1]
| because vibration due to the construction of the tower across
| the street kept destroying hard drives in their computing
| center.
|
| [1] https://en.wikipedia.org/wiki/330_North_Wabash
| mananaysiempre wrote:
| Obligatory link to Brendan Gregg shouting at hard drives:
| https://www.youtube.com/watch?v=tDacjrSCeq4.
| js2 wrote:
| Gosh I hope there are some lucky 10K seeing this today.
| stavros wrote:
| I was one!
| CalChris wrote:
| I used an iPhone as an air pressure recorder. There's an app
| for that; many actually. Anyways, the trunk gate on my car
| wasn't sealing and when it went over pavement joints on the
| highway it would slightly open and then close in quick
| succession which was nauseating. I showed the data to Tesla
| service and they (grumbled and) readjusted the trunk gate. The
| problem disappeared.
| dtgriscom wrote:
| I wrote that software, called SeisMac. Someone figured out the
| Apple-private API for the Sudden Motion Sensor that parks your
| laptop's hard drive if it detects free-fall. Working from that,
| I wrote a free app that used the API to show three-axis
| acceleration graphs. I was proudest of the calibration utility,
| which had you tip your laptop on its side (with properly
| rotated dialogs!), and then on its screen.
|
| People would send me recordings from all over the world (e.g.
| on a ship in the Drake Passage showing enormous surges). It was
| a lot of fun, and I even got an educational grant to improve
| it.
|
| Big bummer when Apple switched to solid-state drives (well, a
| bummer for my one small reason...)
|
| [0]: https://en.wikipedia.org/wiki/Sudden_Motion_Sensor
| incanus77 wrote:
| Awesome, the name rings a bell now! Thanks for that. Honestly
| didn't remember the software involved (nowadays, I'd mention
| it in the blog post).
| theyknowitsxmas wrote:
| Apple would've made an app a long time ago but would get sued
| after someone put a tire on it.
| mrexroad wrote:
| I can already picture the Reddit post of an inverted aeropress
| brew fail while using trackpad as scale.
| mig39 wrote:
| Very cool, Krish! Hi from Fort McMurray! I'm going to use this
| project as an example for a Computer Science class.
| ynniv wrote:
| Finally some _hacker news_
| ivanjermakov wrote:
| > TrackWeight utilizes the Open Multi-Touch Support library by
| Takuto Nakamura to gain private access to all mouse and trackpad
| events on macOS. This library provides detailed touch data
| including pressure readings that are normally inaccessible to
| standard applications.
|
| How can something be available as a library but not as a native
| interface? Swift does not expose that API?
| bri3d wrote:
| Mac OS has "Private Frameworks" - shared libraries that are
| used by the system but don't ship with headers by default. It's
| trivial to produce these headers from the libraries, and then
| make wrappers for them like OpenMultitouchSupport which is a
| wrapper for MultitouchSupport.framework.
| anxman wrote:
| But just to note, I believe you can't pass Gatekeeper/Notary
| if you use these APIs so it's not possible to sign the app
| jordanmorgan10 wrote:
| Back when we had 3D Touch, there was UIForce which did this. I
| still lament the loss of 3D Touch to this day :-(
| volemo wrote:
| It was such a useful feature! I mourn it every time I try to
| save a picture from Google and iOS selects nonexistent text
| around it. :(
| arm32 wrote:
| I must not use this for weed, I must not use this for weed, I
| must not use this for weed
| dmd wrote:
| Why not?
| ThatMedicIsASpy wrote:
| Weed can be sticky depending on the strain/harvest/cure time
| arm32 wrote:
| The sticky icky would completely destroy my beautiful, black
| M3 MBP.
| flotzam wrote:
| https://en.wikipedia.org/wiki/Weighing_paper
| jahantech wrote:
| This is exactly why normal people call us geeks "weird". Keep
| bringing on the cool stuff!
| mikpanko wrote:
| Very cool. Curious: what is the minimum and maximum weight
| MacBook's trackpad can reliably measure this way?
| fnord77 wrote:
| What's the weight range it can handle? no mention of it and I
| don't want to dig through code
| projektfu wrote:
| Could it be used to provide gait analysis for your pet mouse?
| subdev wrote:
| How does one come up with this idea?
| pavon wrote:
| I love this, such a creative hack, and the wonderful irony that
| it only works when one has their finger on the scale.
|
| * Not legal for trade outside of Ankh-Morpork.
| koiueo wrote:
| Finally, some actually useful usage scenario for that oversized
| trackpad
| byyoung3 wrote:
| great work
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