In 2022, even the simplest push-button phones are equipped with many smart sensors and even processors, which makes them an order of magnitude smarter than their distant relatives. What can we say about smartphones: proximity sensor, lighting sensor, gyroscope and accelerometer are only a small part of the smart stuffing of your phone. Of all these smart sensors, the Hall sensor stands out especially, about which not much is known. What kind of sensor is this? How does he work?
Why do you need a Hall sensor in a smartphone?
What is a Hall sensor
A Hall sensor is a smart sensor that detects the magnetic field and its strength. In everyday life it is quite cumbersome, so a smartphone uses a more simplified analogue of this device, which reacts only to the presence of a magnetic field. The device is based on the principle of the Hall effect, which was discovered in 1879. The bottom line is that if the conductor through which electric current flows is in a constant magnetic field, under this action the electrons are deflected towards one of the faces of the plate. This part accumulates a negative charge, and the opposite part accumulates a positive charge. As a result, the potential difference formed at the edges of the plate is recorded by a sensor. In a smartphone, this sensor is a microcircuit that represents a binary code.
The Hall sensor looks exactly like this when analyzed
Smartphone manufacturers are not using this sensor to its full . There are several reasons for this: for example, this is hampered by the lack of free space in the smartphone case, weak batteries that cannot cope with the voracious sensor. In addition, the sensor is used exclusively for three functions and manufacturers do not have any interest in implementing new functions using it.
Types of sensors
There are several types of Hall sensors, each of which differs in the characteristics of its operation and reactions to the poles of magnets:
- Unipolar. This type is built into small processors, smartphones and tablet computers; the sensor reacts only to one pole of the magnet and produces a signal when it is brought to the device;
- Bipolar. Used in aircraft and rocket science, they react to both magnetic poles, with the only exception that in order to turn off the sensor, it is necessary to bring the opposite pole of the magnet to it;
- Omnipolar. This type is similar to unipolar sensors, but the controller itself reads the signal from both the north and south magnetic poles, therefore it is considered more sensitive, although it takes up more space.
Why do you need a Hall sensor in a smartphone?
The sensor is used for three important functions. Firstly, for stable operation of GPS and positioning. With its help, navigation maps speed up the determination of your location, which allows the system to work with high accuracy and without long delays when turning on navigation maps. What are the best cards to use? Read in our Yandex.Zen!
Hall sensor helps with GPS operation
The most striking example of everyday use of a Hall sensor is smartphones or tablets with magnetic cases, styluses and keyboards. Perhaps this is the most important advantage, which we will discuss below. The work of the same Smart Cover for iPad is based precisely on this principle, thanks to which the cover is considered smart (and costs more).
Smart sensors: How does a gyroscope work in a phone?
The third function is also important: the Hall sensor allows the operation of folding smartphones and laptops, whose when closed . Previously, this was actively used in flip phones and sliders, but now it has found application in the new foldable Samsung smartphones. The smart sensor is located on one part of the phone, and the other has a small magnet that ends up directly above the sensor. When you close the phone, the sensor is triggered, allowing you to perform some action, such as ending a call or closing an application. In laptops, the Hall sensor is useful in a similar way - when you close the lid, the operating system leaves the computer in sleep or standby mode.
Why is it needed on the phone?
A few years ago, a magnetometer with a dozen capabilities could only be found in flagship smartphones. Now, it is installed in almost every phone. A smartphone equipped with a magnetometer (working on the principle of a Hall sensor) made it possible to measure the electromagnetic induction of various devices, control some phone functions without contact (for example, scrolling through photos using gestures, without physical contact), etc.
Although the magnetometer is installed in many mobile devices, not all of its functions are fully implemented.
This is done for technical (for example, there is not enough space in the design of the phone or to reduce power consumption) and financial (in budget models) reasons. If we remove all the additional functions, the task of the mentioned sensor comes down to two main functions:
- Digital compass. Used by navigation programs to speed up positioning and more accurately determine the direction of movement. Using a sensor, GPS search is faster.
- Interaction with accessories. By purchasing a magnetic case for a smartphone, the sensor will allow the smartphone to turn on and off the display depending on the distance/approach of the magnet on the accessory.
The “display off” effect can be seen when the lid is closed on folding phones.
How does a magnetic case work?
The market is replete with a variety of cases for smartphones, but magnetic book cases that automatically turn off or activate the smartphone screen have always been in particular demand, such as the Smart Case for iPad. How it works? The display is blocked or activated due to the reaction of the Hall sensor in the smartphone to an approaching magnet hidden in the cover of the case. When you open the cover of the case, the radiation intensity decreases, so the screen turns on.
Conventional cases for Samsung Galaxy work with a Hall sensor
The Hall sensor works very conveniently with flip cases that have a small cutout for controlling the player or answering calls. Thanks to this feature, you can use certain functions without opening the case, for example, view notifications from our Telegram chat or check the time. How it works? The possibility of the presence or absence of a high magnetic field allows the smartphone to leave the screen active or illuminate only the required area of the display. By the way, the magnet itself installed in the case does not harm the smartphone.
Interaction between the sensor and the magnetic case
The interaction is implemented in a simple way: when you open the case, the magnet located in the flip moves away from the display. The conductor with the magnetic field breaks, the Hall voltage decreases and the display switching circuit starts. After this, the display will be unlocked.
As you may have guessed, when you close the case the opposite happens and the screen is blocked.
Some cases have windows to display information when the cover is closed. Displaying information and locking the screen follows the same principle. The hall sensor detects the position of the smartphone and “decides” whether to block the phone’s display or leave it on.
If you're worried that the magnet on the flip will damage your smartphone, take that weight off your shoulder. The magnet does not harm the smartphone! To see this, watch the video.
How to check the Hall sensor in a smartphone
Almost all modern smartphones are equipped with this sensor. If you are wondering whether your phone supports this feature, you can go to the manufacturer’s website to search for documentation on the model or check in the “Sensors” section through the AIDA64 utility.
Smart Case for iPad - an excellent use of the Hall sensor
When purchasing a smartphone, ask if smart magnetic cases are available for it. If they exist, then your phone definitely has a Hall sensor. There is another way to manually check the presence of a sensor: take a small magnet and hold it to the smartphone screen. The screen should go dark when you approach it and start glowing when you move the magnet away.
It turned out that the Hall sensor is one of the quite familiar smartphone sensors that we use everywhere. Sometimes we don’t even think that behind such simple things there are huge scientific discoveries.
Miracle cases
I'm sure you've seen book-shaped cases that when closed block the display, and when opened, they automatically unlock. How is this possible?
It is the Hall sensor that provides this behavior. As soon as a magnet (located inside the protective flip) approaches it, the direction of the field changes, the sensor detects the change and the phone software receives the corresponding command - turn off the screen.
Some “book” models have a window for displaying time, messages and other information. How does this happen, since the lid is closed and the display is active? The fact is that the Hall sensor operating principle in a phone can be such that it determines the need for complete or partial blocking of the display.
I suggest watching a more detailed video on this issue:
Advantages and disadvantages
Pros:
- universality (they simultaneously determine position, direction, and so on);
- wear resistance. There are no moving parts, they are solid state, rugged devices, providing extreme durability;
- almost complete independence from the need for maintenance;
- The Hall effect current sensor operates under vibrations, in dusty, humid, aggressive conditions, and at high temperatures.
Minuses:
- standard devices have a maximum distance to the measured current of about 10 cm. But it all depends on the magnet: if it is powerful and creates a wide field, then the distance increases;
- a characteristic “disease” is accuracy, since there is a dependence on the magnetic field, and other external similar phenomena can introduce distortions. The same applies to high temperatures, since they change the resistance of conductors, and accordingly, the mobility of charge carriers, but here sensitivity suffers. However, this is rare or the effect is negligible; in general, it does not particularly affect the work.
Disabling the sensor
You cannot disable the sensor using the settings - such a function is not provided in either Android or iPhone. In some ZTE models, the manufacturer independently added this feature. You can also do this if you have root rights (for Android devices) by installing the Xposed module. But there is little point in this, since the Hall sensor consumes a tiny amount of current (approximately 0.05% of the battery capacity during the entire discharge cycle). If you need to disable interaction with the case, it is easier to remove the magnet from it.
So, the sensor is used to measure the polarity of the magnetic field. It is used primarily for interaction with branded accessories (cases, styluses, keyboards) and for the operation of a digital compass. Perhaps in the near future manufacturers will find other options for its use. For example, in China it was proposed to use it to determine background radiation (when exposed to it, the polarity on the conductor also changes).
Magnetic cases
You've probably seen so-called magnetic cases for both smartphones and tablets. They allow you to lock and unlock the device when opening/closing the case.
How is this possible? The Hall sensor installed in the device responds to a magnet located in the case itself. When the magnet is placed close to the device, the sensor detects increased radiation, resulting in the display being blocked. Such cases often have the prefix “Smart”.
When the user opens the flip case (book case), the sensor detects a decrease in radiation intensity and unlocks the screen.
What if the case has a special window that displays information even if the case is closed? In this case, the Hall sensor is also used - it gives a command to switch between different display operating modes, that is, it displays only certain information in the window, for example, time, date, notifications. An example of such a case is from Samsung:
And by the way, if you use a screen created using AMOLED technology, due to the peculiarities of the technology, the information displayed in the window has practically no effect on the energy consumption of the battery.
The principle of interaction with a magnetic case
Interaction with magnetic cases is the most common use case for a Hall sensor.
It works like this:
- When the display is covered with a case, it turns off or goes into the mode of showing the time and current notifications (if such a function is provided by the built-in OS, there is a cutout or “window” in the case itself).
- When the display is not covered with a cover, it operates as usual.
The magnet to which the smartphone responds is located in the front protective part of the case, which covers the display. When the case is opened, the magnet moves to the side, which is what the phone reads. If the magnet is removed, the smartphone will not respond to the case.
