Proximity sensor in the phone - what is it? Cell phones

Many modern electronics products are equipped with sensors that recognize the approach of an object, for example, a finger, to the keyboard or the person's ear to the phone. This technology is actively used in touch panels of all kinds, which allows eliminating the mechanical switching of devices, as well as prolonging their service life. And many may well have a question: the proximity sensor in the phone - what is it and how does it work? Next, this device will be considered from the point of view of implementation by capacitive technology.

Approach recognition

Recognition proximity by contactless technology quickly found application in the field of portable devices that are fed autonomously. The function is actively used in the latest models of smartphones and tablets, in music players. Its main purpose is to increase the reliability of devices and save energy.

The display of the device will be in an inactive state until the user's hand is detected and the proximity sensor in the phone answers for it. What this - will become clear, if we consider the principle of its work. When it comes to the use of such a technology, then it is worth noting that in the standby mode, only the CPU is concerned with power consumption. And when non-contact sensors determine the approach of the palm or finger, the display turns on, where the current information is displayed. All this allows you to reduce the average power consumption of the gadget, while increasing battery life.

Features of using the function in different techniques

In the home automation system, the recognition function of the approximation has also become very widespread. Non-contact sensors are used to turn on table lamps, open water supply tap when the person's hand is in the field of action; The displays of refrigerators and microwave ovens will be inactive until they reach the user's hand. Equipped with this function and new home automation systems. Touchscreens used to control household appliances and lighting are configured to serve as digital photo frames. But as soon as one of the people approaches them, control buttons immediately appear . A rather interesting technology is the proximity sensor in the phone. What it is, will help to understand the description of the method by which recognition occurs.

Approach recognition methods

There are a number of ways, including inductive, resistive, optical, capacitive, visual and acoustic. Each of them has certain advantages and disadvantages. The choice of this or that technology depends on the cost and ease of working with it. Consider the proximity sensor in the phone - that it will help to understand certain information. The most commonly used capacitive proximity sensors. Their principle of operation is quite simple. The sensor with conductors, suitable for it, is hidden under a special protective layer. Two conductive elements in close proximity to each other have a certain parasitic capacitance that arises between the conductive ground layer and the contact pad of the sensor itself. Usually its value is 10-300 picafarads.

When the sensor approaches, for example, a finger, the total capacity of the system changes. This is what is used to detect the object near the contactless sensor.

Capacity change detection

The degree to which the proximity sensor will work reliably and reliably depends entirely on the accuracy of measurements of the changed capacity of the system. For this purpose, a number of methods have been developed, among which the most famous are the methods of charge transfer, successive approximation, capacitance interaction and sigma-delta method. Two of them are most often used. Both use a switchable capacitive circuit and an external measuring capacitor.

The method of successive approximation

In this case, the switched capacitive circuit is charged. From this capacitor, voltage is applied to the comparator through the LPF, where a comparison with the reference voltage occurs. The counter synchronized with the generator is locked using the output signal of the comparator. This signal is processed for a specific sensor status. For the method of successive approximations, an insignificant number of external components is required. In this case, the operation of the circuit is not affected by transient interference in the supply circuit.

Advantages and disadvantages of recognition technology

The Android proximity sensor, like others, has certain characteristics. Among the advantages in this case are the following:

- a fairly large detection area;

- high degree of sensitivity;

- relative availability in terms of price, because the production of sensors is made from fairly cheap components - copper, tin oxide film, indium and printing ink, external wire sensor;

- small size;

- universality of design;

- temperature stability;

- the possibility of functioning with the use of various non-conductive coatings, for example, glasses of different thicknesses;

- durability and high reliability.

There are certain drawbacks to this method:

- the sensing element must be conductive, then it will be able to detect the approximation; However, the hand, for example, in a rubber glove, it may not be found;

- Being near a conductive object can cause the system to recalculate the parasitic capacitance in such a way as to take into account changes that are caused by this object. This often causes false positives in the future, but the calibration of the proximity sensor will eliminate this trouble;

- The capacitive recognition method works so that when there are metal objects in the range of its operation, the range decreases.

IPhone 4 screen lock

The proximity sensor works in such a way that you can turn off the smartphone screen during a call to prevent accidental keystrokes. There are special applications that make it possible to block the screen by simply passing a hand over it. To enable it, you need to press the hardware key.

Calibration

Quite often, users are faced with an unpleasant situation, when the screen lock during a conversation is not carried out. And it also happens that after the end of the conversation the display does not turn on, because of what the phone will not be unlocked. For example, the Nokia proximity sensor does not work correctly. To eliminate this problem, it needs to be calibrated. Usually most manufacturers use specialized software for these purposes, which can be downloaded on the official website.

In the latest versions of Android 4, the calibration function is located directly in the menu. To do this, enter the settings, find the screen, and then select Proximity Sensor Calibration. After closing the sensor with your hand, press OK in the window that appears. Sometimes calibration is allowed without closing the sensor.