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How does your phone know when to rotate the screen?

You were watching a video on YouTube in portrait mode, and the screen real estate wasn’t enough. To solve this problem, you did what anyone with a smartphone would do. Turn the phone on its side.


As soon as you did this, the video took up the entire screen, and all menu options were invisible, but how did your phone know about its orientation?

Well, apart from the high refresh rate screen and a great user interface, your phone has several sensors that detect its orientation in space, but how do these sensors work?


Understanding the fundamental forces of nature

Although you can feel the wind on your face and the water on your hands when it rains, what you cannot feel are the fundamental forces of nature.

These forces include the gravitational force and the electromagnetic force. Although these forces are intangible, they influence everything we do. In fact, the screen of your smartphone detects tiny changes in electromagnetic forces for your finger to detect. Not only this, the weight of your body is also defined due to the force of gravity.

Simply put, gravity exerts a force on objects causing them to accelerate at a speed of 9.8 m/s^2. Due to this acceleration, things fall back to the ground when thrown.

On the other hand, the electromagnetic force cannot be felt like the gravitational force. That said, if you put a compass anywhere in the world, it will detect the Earth’s magnetic field in that region and align itself to the North Pole.

Although electromagnetic forces have enabled many technological advances, they are not all for good, and electromagnetic radiation in high amounts can be dangerous to the human body.

Understanding sensor technology on your smartphone

Your smartphone’s sensors detect changes in the forces of nature to sense the orientation of nature in space, but how do these sensors work?

Well, there are thousands of sensors on your smartphone’s motherboard, but there are three main sensor types that enable your phone to detect changes in its orientation.

These orientation detection sensors use micro-electro-mechanical systems (MEMS) to measure the forces of nature. To measure the data, MEMS devices use mechanical parts embedded in silicon to generate an electrical signal. Using these signals, your smartphone detects changes in the forces acting on it.

Below is a brief description of how these sensors work.

  • Accelerometer: As the name suggests, the accelerometer is used to detect the change in acceleration on the smartphone. To detect these changes, the accelerometer uses the law of inertia, which states that a body will remain at rest as long as no external force is applied. To use this concept, a fixed mass is suspended between spring-like structures in a MEMS sensor. Therefore, when the springs are compressed due to the inertia of the phone, the fixed mass remains in place. This spring compression generates an electrical signal telling the smartphone that it is being accelerated.

  • Gyroscope: The gyroscope monitors the rotational forces on your smartphone. This rotation measures the Coriolis force acting on the smartphone to estimate how much it has rotated about its center of gravity. Simply put, the Coriolis force is the force acting on any body due to the rotation of an object moving inside it. The gyroscope uses the same design as the accelerometer but is modified to detect changes when the smartphone is rotated.
  • Magnetometer: Due to the currents flowing in the Earth’s core, a magnetic field engulfs it. Detecting these regions helps the smartphone to sense its orientation along the true north of the Earth’s magnetic field. Smartphones are equipped with three-axis Hall effect sensors to detect these changes. This sensor uses Faraday’s laws of electromagnetic induction to detect the magnetic field. According to this law, a current carrying conductor produces an electromotive force when the magnetic field around it changes. Because of these changes in voltage, sensors can be used to detect its orientation with respect to the Earth’s magnetic poles.

Now that we have a basic understanding of the sensors in our smartphone, we can see how they work together to detect the position of your smartphone.

How does your phone know when to turn on the screen?

As mentioned earlier, the accelerometer can detect changes in acceleration, but this data alone cannot be used to detect the orientation of the smartphone. This is because the forces of gravity are always acting on the accelerometer, and it is difficult for the sensor to detect when a change in acceleration occurs to rotate the smartphone.

Smartphones use sensor fusion to solve this problem, which enables different sensors to communicate with each other. To detect the orientation of the phone, the accelerometer communicates with the gyroscope and magnetometer.

So, when a phone spins, the accelerometer detects the change in acceleration and then communicates with the gyroscope. Because of this communication, the smartphone can understand whether the change in acceleration is for rotation or not.

That said, the gyroscope is susceptible to errors because it cannot consider the gravitational forces acting on the smartphone. Hence, a third sensor is needed to detect the change in orientation of the smartphone. This sensor is none other than the magnetometer on your device.

This magnetometer is used to detect changes in the position of the smartphone with respect to the Earth’s magnetic field. This data, along with data from the accelerometer and gyroscope, is used to decide whether your screen should be in portrait or landscape mode.

Is sensor technology the future?

Accelerometers, gyroscopes and magnetometers use the laws of inertia and electromagnetic induction to detect changes in the fundamental forces of nature.

Smartphones use these fundamental laws to enable features such as autorotation and optical image stabilization. That said, smartphones now offer innovative features by combining data from different sensors.

A prime example of this is the release of crash detection on Apple devices that enables data from these sensors to detect a crash and alert emergency services.

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