I wonder why? Presumably this information doesn't come for free, and Apple spends money to put this sensor in.

Is it a backup if the magnet for closed lid detection fails? Is it some kind of input for the brightness sensor or True Tone? Is it for warranty investigation, that if the hinge breaks they can figure out if it was physically pushed too far, or was repeatedly slammed open and shut like a toy?

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avianlyric 7 days ago | parent | next [-]

The info probably does come for free. The laptops don’t use the magnets along the top edge of the screen for detecting if the screen is closed, those magnets are just there to provide the latching effect when the screen is closed, so it doesn’t open accidentally.

The sensor used for detecting if the lid is closed is an “angle” sensor, although really it’s an Hall effect sensor and a magnet in the hinge. If you have a Hall effect sensor, getting angle data from it is pretty much free, because the Hall effect produces a continuously varying signal, you need thresholding logic to turn it into a binary output.

Given Hall effect ICs are so cheap and plentiful there no reason to use anything else. Also given they mass-produced ICs it’s probably cheaper to buy a fully featured Hall Effect IC, because the manufacturing cost between a basic IC and an advanced IC is almost certainly zero these days.

In short, modern IC manufacturing has just made magnetic angle sensors as cheap, if not cheaper, than dump non-angle sensing Hall sensors. After all you can always use an angle sensing Hall sensor as binary switch if you want, but the reverse isn’t true, so if the ICs basically cost the same, you can expect the less capable ICs to be completely outcompeted by the more capable ICs.

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macNchz 7 days ago | parent | next [-]

Once upon a time Mac laptops used reed switches to detect closed lids, and they were a common point of failure, presumably since they contained moving parts.

	▲	cosmic_cheese 7 days ago \| parent [-]
		They can be erroneously triggered or prevented from working as expected by nearby magnetic objects too, which can be annoying. No such issue with a hinge angle sensor.

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londons_explore 6 days ago | parent | prev | next [-]

Angle sensing IC's tend to need to be on the end of the shaft they sense, which can make some packaging and assembly headaches.

I personally am surprised they don't put an accelerometer in both halves of the laptop and use math to calculate the angle based on gravity.

	▲	avianlyric 6 days ago \| parent [-]
		They only need to be co-linear to the shaft if you care about accurate measurements, such as in a motor controller. I doubt the error introduced by being off-axis would make much difference in this application. There are also packaging considerations when putting a hall sensor elsewhere. Packaging it in the hinge has the advantage you can use the same hinge and sensor setup in all laptop models. Packaging the sensor elsewhere means custom packaging setups for each laptop to work around all the other components in the body of the machine. Doing the extra work for packaging in the hinge once is probably quite a bit cheaper than having to constantly redo the packaging work in every new model.

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ChocolateGod 7 days ago | parent | prev | next [-]

So basically as free as the glowing Apple logo that used to be on the back of Macbooks.

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userbinator 6 days ago | parent | prev [-]

The cost of the software is higher for an angle sensor than a binary switch, but perhaps they consider it NRE (which is actually not true if you consider "maintenance" work.)

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estimator7292 7 days ago | parent | prev | next [-]

We've been using Hall effect sensors for lid close detection for a long, long time. My thinkpad from 2013 has it halfway down one edge.

If you simply move the sensor (that is already a requirement) closer to the hinge, you can infer angle based on the Hall sensor for free. You can even get special sensors that specifically measure the magnetic field orientation for the same price as the simple type.

Yes, it's completely free with just a very minimal amount of thought put into the design.

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postalcoder 7 days ago | parent | prev | next [-]

It’s likely there to support Desk View[0]. Desk View presents the items on your desk in a geometrically correct, top-down view. Knowing the angle of the display is very helpful when applying keystone correction.

0: https://support.apple.com/en-us/121541

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rossant 7 days ago | parent | prev | next [-]

Wild idea: if the goal is to wake from sleep as quickly as possible when opening the lid, could receiving a signal as soon as the user starts lifting the screen save a few hundred milliseconds? I might be way off though.

	▲	anentropic 7 days ago \| parent [-]
		Pretty sure that exact feature was announced when the current generation of Macbooks were launched

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seanalltogether 7 days ago | parent | prev [-]

My best guess is it's related to thermal control. The vents on macbooks are right under the hinge, and the vents are blocked and opened to different degrees based on the angle of the lid.