Many products of modern electronics are equipped with sensors that recognize the proximity of an object, such as a finger, to the keyboard or a person's ear to the phone. This technology is actively used in touch panels of various kinds, which eliminates the mechanical switching of devices, as well as extending 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 using capacitive technology.
Proximity detection
Proximity recognition using non-contact technology quickly found application in the field of portable devices that are 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 saveelectrical energy.
The display of the device will be in an inactive state until the approach of the user's hand is detected, which is exactly what the proximity sensor in the phone is responsible for. What it is - it will become clear if we consider the principle of its work. When it comes to using this technology, it is worth noting that in standby mode, only the central processor is engaged in energy consumption. And when the proximity sensors detect the approach of a palm or finger, the display turns on, which shows 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 household automation, the proximity recognition function has also become very widespread. Non-contact sensors are used to turn on table lamps, open water taps when a human hand is in their field of action; the displays of refrigerators and microwave ovens will be inactive until the user's hand approaches them. Equipped with this function and new home automation systems. Touch displays used to control appliances and lighting are set up 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 whichrecognition occurs.
Proximity recognition methods
There are a number of ways, among which we can distinguish inductive, resistive, optical, capacitive, visual and acoustic. Each of them has certain advantages and disadvantages. The choice of one or another technology depends on the cost and ease of working with it. Consider the proximity sensor in the phone - what it is, certain information will help to understand. The most commonly used capacitive proximity sensors. Their working principle is quite simple. The sensor with conductors suitable for it is hidden under a special protective layer. Two conductive elements that are in close proximity to each other have a certain parasitic capacitance that occurs between the conductive ground layer and the pad of the sensor itself. Usually its value is 10-300 picafarads.
When a finger, for example, approaches the sensor, the total capacity of the system changes. This is what is used to detect an object near the proximity sensor.
Capacity change detection
How accurately and reliably a non-contact sensor will work depends entirely on the accuracy of measurements of the changed capacitance 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 the sigma-delta method. Two of them are most commonly used. Both useswitched capacitive circuit and an external measuring capacitor.
Successive approximation method
In this case, the switched capacitive circuit is being charged. From this capacitor, voltage is supplied to the comparator through the low-pass filter, where it is compared 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 certain status of the sensor. 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 on the supply circuit.
Advantages and disadvantages of recognition technology
The Android proximity sensor, like others, has certain features. Benefits in this case include the following:
- 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 oxides, indium and printing ink, an external wire sensor;
- small size;
- design versatility;
- temperature stability;
- the possibility of functioning with the use of various non-conductive coatings, for example, glasses of different thicknesses;
- durability and high reliability.
This method also has certain disadvantages:
- sensitivethe element must be conductive, then it can detect the approach; however, a hand, for example, in a rubber glove, may not be detected;
- being close to a conductive object may cause the system to recalculate the parasitic capacitance so as to take into account the changes caused by this object. This often causes false positives in the future, however, calibrating the proximity sensor will eliminate this nuisance;
- The capacitive detection method works in such a way that when there are metal objects in its range, the range decreases.
iPhone 4 screen lock
The proximity sensor works in such a way that it allows you to turn off the smartphone screen during a call to prevent accidental keystrokes. There are special applications that allow you 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, which is why the phone does not unlock. For example, the Nokia proximity sensor does not work correctly. To fix this problem, it needs to be calibrated. Usually, most manufacturers use specialized software for these purposes, which can be downloaded from the official website.
In the latest versions of Android 4, the calibration functionlocated directly on the menu. To do this, you need to enter the settings, find the screen, and then select the Proximity Sensor Calibration item. After closing the sensor with your hand, press OK in the window that appears. Calibration is sometimes allowed without covering the sensor.
