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Application of Hall Switch on TWS Earphones

As TWS Bluetooth earphones are gradually known to everyone, the components related to TWS earphones have slowly entered into everyone's field of vision. Friends who have the Bluetooth TWS earphones know that if the Bluetooth earphones are always on, the power consumption will be very fast. If it is turned off manually, it must be turned on manually when it is used again. The charging compartment first solves the problem of the battery life of the Bluetooth earphones. In order to make the product more convenient to use, how to cancel the manual on/off function?

Friends who have Apple Airpods II and Airpods Pro know that after opening the cover, the Bluetooth earphones will automatically connect with the mobile phone. A seemingly simple function, but do you know the principle? This is a very small component that we are going to talk about todaythe pop-up HALL SWITCH, which greatly improves the convenience of the product and can help reduce the power consumption of Bluetooth earphones.

1. What is a Hall Switch?

The Hall element is a kind of magnetic sensitive element. A switch made of Hall elements is called a Hall switch. When the magnetic object moves closer to the Hall switch, the Hall element on the switch detection surface changes the internal circuit state of the switch due to the Hall effect, thereby recognizing the presence of a magnetic object nearby and controlling the switch on or off. The detection object of this proximity switch must be a magnetic object.

2. Hall switch Classification

Hall switch is divided into unipolar, bipolar and omnipolar

1. The induction method of the unipolar Hall switch a magnetic pole of the magnetic field is close to it, and a signal of low potential voltage (low level) or off is output, and the magnetic pole of the magnetic field leaves it and outputs a signal of high potential voltage (high level) or on However, it should be noted that the unipolar Hall switch will specify a certain magnetic pole induction to be effective, generally the positive side induction magnetic field S pole, the reverse side induction N pole.

2. The induction method of the bipolar hall switch because the magnetic field has two magnetic poles N and S (positive or negative magnetism), the two magnetic poles respectively control the on and off of the bipolar hall switch (high and low level) , It generally has a locking effect, that is to say, when the magnetic pole leaves, the Hall output signal does not change until another magnetic pole is induced. In addition, the initial state of the bipolar Hall switch is a random output, which may be high or low.

3. The induction method of the omnipolar Hall switch The induction method of the omnipolar Hall switch is similar to the induction method of the unipolar Hall switch, the difference is that the unipolar Hall switch will specify the magnetic pole, and the omnipolar The Hall switch will not specify the magnetic pole, any magnetic pole is close to the output low level signal, leaving the output high level signal.

3. Hall switch Bluetooth earphones induction principle

l Sports Bluetooth earphones and headphones Hall switch principle

The magnetized Bluetooth earphones has magnets on the left and right sides, and the patch Hall switch is located in the left and right ears, relying on the opposite magnet to sense it. When the left and right ears of the earphones are attracted to each other, the Hall switch relative to the magnet is turned off and the Hall switch senses the magnetic field. A single-pole Hall switch then triggers and the earphones turn off. When the left and right earphones are removed separately, the magnets are away from the Hall switch. At this point, the Bluetooth earphones Hall switch has no magnetic induction, a high level output, and a trigger signal, and the earphone is ready to use. Since Hall switches are based on magnetic field sensing, the Hall switch chips used in different earphone structures will be different, insulating the components from magnetic field interference. Nowadays, there are a lot of products that are used in life, such as Hall switches, cars, home appliances and electronic products, which are a little bit more.

l TWS earphones Hall switch working principle

A magnet is placed inside the charging case cover, and a Hall sensor is placed inside the charging case near the upper cover. When the Hall sensor detects the magnet, it will transmit the changed signal to the main board of the charging case. The main board sends out a series of signals to communicate with the Bluetooth earphones to notify the Bluetooth earphones to connect to the mobile phone.

In order to be convenient to carry, the general volume will not be very big. Except for the battery, circuit board, and earphones, there is not much space left. In this narrow space, the charging case needs a magnet to attract the cover. Earphones also need magnets, resulting in many number of magnets. The magnetic field of each magnet may induce the magnetic field strength of the Hall sensor. If it is disturbed by the magnet in the charging case, the Hall cannot react normally to the magnet on the cover. A common problem is that the cover is opened and Bluetooth will not automatically connect; or the cover is closed and the earphones will not be automatically charging, so the magnets in the Bluetooth earphones must be placed in different directions.

Under normal circumstances, it is difficult to achieve that the magnetic field of the Hall sensing point is 0 after opening the cover. Assuming that the magnetic field strength at this time is + 30GS, an omnipolar Hall switch is selected. After opening the charging case cover, the magnetic field on the cover is removed, and the Hall will also be triggered by the magnetic field in the charging case. In order to solve this problem, we need a Hall that only operates on -30GS, and can avoid the interference of + 30GS. Then put a strong magnet of -30 GS or above on the charging case cover. When the cover is closed, the Hall is triggered. After opening, the Hall induced magnetic field returns to + 30GS again, and the Hall returns to normal.

4. Sensitivity of Hall switch

In the process of customer product development, some engineers responded that the sensitivity of the Hall switching element is not good. In fact, in practical applications, most Hall ICs can trigger work when the surface reaches about 30GS. If the sensitivity is not enough, refer to the product specification. There is a parameter standard for the magnetic trigger value. According to the parameter value, determine the size of the magnetic magnetization to see if it can meet the requirements of the Hall switch. It is also necessary to determine whether there is an obstacle between the Hall switch and the magnet. The loss of this process must be verified repeatedly. Because Hall sensors have an error interval, there must be an interval value that can be adapted when determining the magnetic size and the sensing distance. The simple steps are as follows

1. Make sure the magnet strength meets the requirements of Hall switch parameters

2. Adjust the sensing distance between the Hall switch and the magnet to see if there are other obstacles

3. Adjust the resistance of the Hall switch is correct

Remarks The sensing distance of Hall switches currently on the market is between 0-20mm, depending on the sensitivity of the Hall components and the magnet magnetism. The magnetism of the current magnets is between several hundred GS and several thousand GS It can be strengthened and weakened, only the magnet supplier needs to be magnetized or demagnetized through professional equipment.

Now you know how the Hall switch works. I think you will know whether you have the function of your products.

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