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The proximity sensor is found in almost all smartphones and has several uses.
He is in charge, among other things, of disabling touches on the screen and turning it off during a call. It was the main application of this sensor in the beginning, and today it is used in many ways. For example, newer phones have an auto-dial option when you hold the phone to your ear while the contact is open, or while reading a message. Many applications use this sensor, e.g. push-up applications where the sensor has the role of counting push-ups by putting the phone under your head and when you do the push-up you get closer to the sensor and it registers it and increases the number by one. Some applications use this sensor to register if the phone is in your pocket and thus prevent accidental unlocking of the phone.
There are many examples, but you are probably wondering how it works?
It is very simple: the proximity sensor emits infrared light (IR - infrared) which is reflected from the object and returned to the photodiode. If no object is nearby, infrared light cannot be reflected and the photodiode does not receive any signal.
However, the infrared beam differs in the color of the surface from which it is reflected, so mistakes were made earlier and the screen was turned on during the conversation. A test was performed with a white, gray, and black surface and the photodiode did not receive a signal when the beam was supposed to bounce off the black surface. This was a problem for those with black hair.
This problem was soon solved by making an "all in one" package of VCNL4020 sensors where IR, photodiode, and ambient light sensor work together.
The light sensor is also present in almost all smartphones and serves to detect ambient light, ie. light reaching the sensor in different conditions. You are probably familiar with the fact that when you turn on the option of automatic adjustment of the screen brightness, the brightness decreases when you go inside and increases when you go outside. This is controlled by this sensor.
Combined with it, the IR and photodiode work perfectly and there are no more errors. The photodiode successfully detects black objects, ie all objects that approach.
That would be the basic principle of the proximity sensor in smartphones. And if you have a phone like this, you can find these sensors somewhere next to the speakers on the front of the phone. When the room is dark, you can see how this sensor lights up when it is active.
Various apps test the sensors on your phone, and one of them is an app for Android devices called Sensor Box you can download it from this link https://play.google.com/store/apps/details?id=imoblife.androidsensorbox
When you open the app, select Proximity Sensor and test by bringing your hand closer to this sensor.
Izvor: thecodeartist.blogspot.com, Smartphone Proximity Sensing By Jim Toal
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