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Comment by euroderf | Hacker News Reader

> trackpads that you'd swear are actually physically clicking

Like my Mac's trackpad ? Can someone ELI5 how it works ? It's gotta be magic-adjacent cos when the machine locks up, the trackpad is deader than a doornail.

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It's the same technique of the "3D touch" the iPhone 6S had, though that was discontinued. Capacitive sensors measure microscopic changes in the glass, as it slightly flexes when you press it. Then a haptic motor does a little kick to simulate the feel of it being pressed down.

They've been doing this since 2015 or so. Prior Macs didn't click on the top 1/4 of the trackpad, because there was basically a "hinge" there and the glass would actually press on a physical button.

So there's a big big matrix of tiny tiny motors under the trackpad ?

no, it sends a large “click” across the whole surface which your finger registers as a local click, they have two large and two small haptic motors in a line iirc and they do some software magic to cancel out the click so it feels extremely localised.

I just tried on my macbook trackpad and if I rest a finger in on part and click with a finger in another part both fingers feel the click. But I suspect this is a feature, not a bug, for multi-touch interfaces.

This sounds very complex and it explains why nobody explains it :)

I wonder if there's a teardown that has really dug into it.

Fun fact, the other thing that can cause this is a Bluetooth mouse in a backpack that is being clicked continuously. Confused me to no end for fifteen minutes.

Have noticed exactly this behavior as well, it's one of the better indicators actually the system ain't coming back.

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