Many products of modern electronics are equipped with sensors that recognize the proximity of an object, for example, a finger, to the keyboard or a person’s ear to the phone. This technology is actively used in various types of touch panels , which eliminates the mechanical switching of devices and also extends 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.
Proximity recognition
Non-contact proximity proximity technology quickly found application in the field of portable devices that powered 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 electrical energy.
The device’s display will be inactive until an approximation of the user's hand is detected, which is precisely what the proximity sensor in the phone is responsible for. What is it - it will become clear if you consider the principle of its work. When it comes to the use of such technology, it is worth noting that in standby mode only the central processor is engaged in energy consumption. And when proximity sensors determine the proximity of the palm or finger, the display turns on, which displays the current information. 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 home automation, the proximity recognition function is also very widespread. Non-contact sensors are used to turn on table lamps, open water taps, when a person’s hand is in their field of action; displays of refrigerators and microwave ovens will be inactive until the user's hand approaches them. Equipped with this feature and new home automation systems. The touch displays 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, the control buttons immediately appear . Quite an 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, among which are inductive, resistive, optical, capacitive, visual and acoustic. Each of them has certain advantages and disadvantages. The choice of a particular technology depends on the cost and ease of working with it. Consider the proximity sensor in the phone - what is it, it will help to understand certain information. Most commonly used are capacitive proximity sensors. Their principle of operation is quite simple. A sensor with conductors suitable for it is hidden under a special protective layer. Two conductive elements located in close proximity to each other have a certain parasitic capacitance that occurs between the conductive ground layer and the contact area of the sensor itself. Usually its value is 10-300 picafarads.
When a finger approaches, for example, a finger, the total capacity of the system changes. It is it that is used to detect an object near a proximity sensor.
Capacitance Detection
How accurately and reliably a non-contact sensor will work depends entirely on the accuracy of measurements of the changed system capacity. For this purpose, a number of methods have been developed, among which the methods of charge transfer, successive approximation, the interaction of capacitance and the sigma-delta method have become the most famous. Two of them are most commonly used. Both use a switched capacitive circuit and an external measuring capacitor.
Sequential Approach Method
In this case, a switched capacitive circuit is charged. From this capacitor, voltage is supplied to the comparator through the low-pass filter, where a comparison is made with the reference voltage. The counter synchronized with the generator is locked using the output signal of the comparator. Processing of this particular signal is carried out for a specific sensor status. The method of successive approximations requires a negligible number of external components. In this case, the operation of the circuit is not affected by crosstalk along the supply circuit.
Advantages and disadvantages of recognition technology
The Android proximity sensor, like others, has certain features. Among the advantages in this case include the following:
- a fairly large detection area;
- high degree of sensitivity;
- relative affordability in terms of price, because the production of sensors is carried out from fairly cheap components - copper, a film of tin oxide, indium and printing ink, an external wire sensor;
- small size;
- universality of design;
- temperature stability;
- the possibility of functioning using various non-conductive coatings, for example, glasses of different thicknesses;
- durability and high reliability.
This method has certain disadvantages:
- the sensitive element must be conductive, then it can detect an approach; however, he, for example, in a rubber glove, may not be able to detect it;
- being close to a conductive object can cause the system to recalculate stray capacitance so as to take into account changes that are caused by this object. This often causes false alarms in the future, however, calibrating the proximity sensor will eliminate this nuisance;
- 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 so that it allows you to turn off the smartphone screen during a call to prevent accidental keystrokes. There are special applications that make it possible to lock the screen by simply swiping your hand over it. To turn it on, you need to press the hardware key.
Calibration
Quite often, users are faced with an unpleasant situation when the screen is not locked during a conversation. And it also happens that after the end of the conversation the display does not turn on, because of which the phone does not unlock. For example, the Nokia proximity sensor does not work correctly. To fix this problem, you need to calibrate it. Typically, 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 the Proximity Sensor Calibration item. After closing the sensor by hand, click OK in the window that appears. Sometimes calibration is allowed without closing the sensor.