How do devices like phones or ipad know which way is “down” for them to auto rotate?
In: 13
They use a device called an accelerometer. This measures gravity and acceleration.
The accelerometer in your phone is a tiny device built into a microchip – but it basically consists of a microscopic weight suspended on magnetic springy suspension and made to bounce like a pendulum with clever electronics. If the springs are pointing up and down, then the weight will take longer to bounce up (because gravity pulls it down, fighting the spring which is pulling it up) and take less time to bounce down (because gravity pulls it together with the spring). The electronics can tell by timing the bouncing. If the bouncing is even, then the springs are flat to the ground. If they are uneven, then one spring is higher than the other.
In order to make sure that this works whichever angle you hold the phone, typical accelerometer chips actually contain 3 accelerometers each at 90 degrees to each other – so that all 3 dimensions get measured.
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