TrackWeight: Turn your MacBook's trackpad into a digital weighing scale | Hacker News Reader

TrackWeight: Turn your MacBook's trackpad into a digital weighing scale

github.com

620 pointswtcactus148 comments

There used to be iPhone apps that did something similar -

https://www.theverge.com/2015/10/28/9625340/iphone-6s-gravit...

If anyone happens to be using an iPhone 6S... http://touchscale.co/

This worked all the way up through the iPhone Xs.

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.

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..

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.)

> 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.

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.

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.

For what it’s worth, I made the same parsing error upon first read.

stiffness != strength

Nobody? Really? It’s definitely the UX feature I miss most on modern iPhones. Long press feels janky in comparison.

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

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.

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 firmer 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.

You can still move the cursor by long pressing on the space bar, in case you didn't know. There's no equivalent replacement for the selection behavior you're describing, though (as far as I'm aware).

I don't understand why Apple doesn't just let us slide to move the cursor, who needs force touch?

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.

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.

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.

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.

For many, old people are the reason the rest of us have nice things.

Apple UX is generally very bad, especially around discoveribility.

  iPhone 6s and 6s Plus (2015) - First to introduce 3D Touch
  iPhone 7 and 7 Plus (2016)
  iPhone 8 and 8 Plus (2017)
  iPhone X (2017)
  iPhone XS and XS Max (2018) - Last models with 3D

Interesting that the iPhone SE 2nd/3rd generation with iPhone 8 form factor do not have 3D touch but "Haptic touch" instead.

https://archive.li/KtfxO

My memory was that the weight API was made private because they didn’t want people using iPhones for drug deals.

Apple, policing use of an API on a privately-owned device for purposes of a consensual, non-violent activity that is only technically a crime in some legal jurisdictions? Sounds about right.

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.

Dropbox shouldn’t exist either bc we have rsync ;)

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/

It's also not the same thing as Dropbox was offering: that's a description of a network drive, but the key thing about Dropbox is that it's a syncing engine. It's a much harder thing to do, but with very big benefits: much faster (since it's just reading off disk) and offline access.

I'm adding this to my list of obscure tools I have in the back of my head

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.

I've use Sensor Logger[1], which does the same. I enjoy following its development.

[1]: https://github.com/tszheichoi/awesome-sensor-logger

Wait, I know this one. You give the barometer to the superintendent if he tells you the height of the building.

how about stacking the barometers ?

Do I measure the passenger plane with or without the ship?

It's pronounced thermometer. :-)

Not everyone got the Niels Bohr joke that you subtly pulled there.

Neat. This method also assumes constant ambient pressure and temperature, and an ideal ziplock bag. (I.e., not stretchy, completely convex, and zero leaks.)

I don't think stretch would matter, or even leaks for that matter. It'd still find equilibrium at the same pressure, no?

3D touch was god tier for FPS games on iOS

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.

Sometimes you can get capacitance to be detected if you hover your finger just millimeters over the trackpad

Can’t you get capacitance with a wet sponge? Like your typical dish cellulose sponge. You could make a small platform?

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

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.

The recipe was on your phone/tablet and there was no way you were taking your gloves off?

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.

I used my nose.

I've done that many times while working on something and my hands are filthy.

My nose-eye coordination leaves something to be desired.

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.

I use this to avoid touching the stupid self-checkout machines when buying groceries

What do you use to avoid touching the carrots and cucumbers?

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)

Could probably make a small stand with nubbins from touch screen pens as the feet.

No, you need roughly a small human's worth of ground mass for most capacitive touch sensors to register a touch.

Tape a wire to the trackpad and hold the wire?

How do capacitive pens work?

You electrically couple to the pen, unless they are active devices, in which case they generate a signal.

That can't be, they work with gloves and things. My gloves even have a thing at the end that works with the touchscreen.

You’ll have to be more descriptive for me to have any hope of answering.

If by your gloves have a thing at the end you mean a patch of special fabric, yes, that fabric conducts from your skin to the screen.

ground mass?

If you don't have ground human presumably you can substitute ground beef or ground turkey.

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.

Looking back, it would have been interesting to code up a program to record the movement of the mouse as a trail of pixels...

If you ever want to do this keep in mind to reconfigure the mouse as a digital pointing device (tablet like), otherwise the mouse acceleration will mess up your position measurement.

On iPhones at least a hack was to rest a metal spoon on the screen and weigh something in the spoon...

Could you accurately weigh a hot dog?

No, only cool ones.

This is a very clever hack, exactly the sort of thing that belongs on Hacker News.

I use a similar approach to weigh objects using gym weighing machine. It doesn't trigger unless there's skin touch.

> 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?

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.

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

Notarisation is not supposed to check for things like this; but you certainly would not be able to ship this to the App Store.

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...

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.

this update breaks my case smacking workflow, please revert

Oh, I vaguely remember someone hacking that for some sort of windowing back then on OS X!

The smackbook pro! https://www.youtube.com/watch?v=6uvQTTPr9Rw

What a great name

That's it exactly. I clearly remember the nonchalantness.

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

Obligatory link to Brendan Gregg shouting at hard drives: https://www.youtube.com/watch?v=tDacjrSCeq4.

Gosh I hope there are some lucky 10K seeing this today.

I was one!

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.

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

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).

The best use of the SMS in the MacBook… or should I say SMACKbook

https://www.youtube.com/watch?v=6uvQTTPr9Rw

Very cool. Curious: what is the minimum and maximum weight MacBook's trackpad can reliably measure this way?

It goes in gram increments and my laptop was able to read 7300g pressing as hard as i could, which I was surprised it would be designed to read that high, might go up to 10kg but I don't want to crack my trackpad lol. The actual measurements though are extremely unreliable. I've found it can't reliably measure anything, measuring a roll of tape gave me measurements from 70g to 700g, it always settled on a number but was different every time. Maybe the underlying data is more accurate but this API is definitely just designed for outputting the force of a finger. M1 MBP for reference

> pressing as hard as i could

you are a brave one

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.

> 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

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.

They have a setting for adjusting the pressure needed to activate a click.

I wonder if that affects this app at all.

The app isn't accurate at all, magic 8-ball of scales, anything you put on the trackpad it'll settle on a weight and give you a number but it'll be random. The app will accurately tell you how much force you're applying with a finger but when putting something else on it'll settle on a random number

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.

Reminds me of this from when I had an HDD Macbook https://uri.cat/software/LiquidMac/

That was such a cool app!

“It mimics the behavior of liquid by creating a particle system that reacts to the computer's orientation.”

Back when we had 3D Touch, there was UIForce which did this. I still lament the loss of 3D Touch to this day :-(

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. :(

This is exactly why normal people call us geeks "weird". Keep bringing on the cool stuff!

Very cool, Krish! Hi from Fort McMurray! I'm going to use this project as an example for a Computer Science class.

Could it be used to provide gait analysis for your pet mouse?

Apparantely on safari there's touch strength so this should be possible to make for the web too, cool

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.)

If you are backpacking with your Macbook, this saves you from also needing to pack a kitchen scale.

I must not use this for weed, I must not use this for weed, I must not use this for weed

Why not?

Weed can be sticky depending on the strain/harvest/cure time

The sticky icky would completely destroy my beautiful, black M3 MBP.

https://en.wikipedia.org/wiki/Weighing_paper

Just what I need to roll the quantitative doobie.

What's the weight range it can handle? no mention of it and I don't want to dig through code

Apple would've made an app a long time ago but would get sued after someone put a tire on it.

I can already picture the Reddit post of an inverted aeropress brew fail while using trackpad as scale.

OT, but this is what i love about apple laptop. They care about small detail, the detail that won't be on spec sheet for advertising.

Like their laptop speaker is superior to any other machine, even premium laptop like xps or surface won't even come close. Or their huge trackpad but still accurate.

I wish other manufacturers copy this from Apple.

https://github.com/grantcarthew/notes/blob/main/macOS/Rant.m...

I was a bit frustrated that the expected precision wasn’t on the main summary screen.

Does anyone know?

Best repo I discovered this month. I love this kind of stuff.

Ah I remember being able to do this with the iPhone 6s

No download link?

I think it's a DIY project.

DIY projects can't be downloaded?

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.

A .dmg or at least a CLI instruction would really help

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.

This is a clever idea, well done!

How does one come up with this idea?

Can someone compile a binary? Don't want to download Xcode just for that...

Finally, some actually useful usage scenario for that oversized trackpad

great work

Finally some hacker news

Very cool, but I'd still probably just buy a cheap digital scale.

The best digital scale is the one you have with you ;)

One less thing to carry.

I used to travel with one of these[0].

[0] https://en.m.wikipedia.org/wiki/Macintosh_Portable

That thing will break your scale.

Yup. Extra batteries were also necessary.

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