Sensor is a kind of detection device that can sense the measured information, and can convert the sensed information into electrical signals or other required forms of information output according to certain rules to meet the requirements of information transmission, processing, storage, display, recording and control. Distance sensor is a big category of sensors, and the working principles of distance sensors with different structures and uses are very different.
The more common distance sensor has two common principles (there are many other principles, but their applications are not very popular):
The first is the time-of-flight method. By emitting and measuring the time from the emission of a specific energy beam to the reflection of the object, the distance to the object can be calculated from this time interval. This specific energy beam can be electromagnetic wave (radar), ultrasonic wave, light, etc. This distance sensor is suitable for long-distance measurement;
The second is the variable flux method. The distance is detected by the different effects of conductive objects on the changing magnetic field at different distances. This kind of sensor is widely used in industry to measure the proximity between metals.
In the field of daily use, because of the low requirements for detection, the distance sensor can be made very simple, and sometimes only one or two components are needed to achieve specific functions. For example:
When the entrance guard or the distance sensor on the door detects whether the door is closed, it only needs to detect whether the door is close to the door frame. At this time, distance detection can be realized only by installing a magnet and a magnetic induction switch at a specific position.
On the mobile phone, the proximity sensor detects the distance between the object and the mobile phone. It is usually only necessary to return to the far state and the near state, that is, the far state and the near state. Some chips integrate the functions of proximity sensor and optical sensor. In fact, a light-emitting diode emitting infrared rays with a specific wavelength is installed next to the light sensor. When there is an object at close range (such as the face when answering the phone), the object is reflected by infrared rays, and the optical sensor next to it will send out a near-state signal when it receives the infrared ray reflection of this specific wavelength. Otherwise, a far state signal is sent. The proximity sensor of the mobile phone can be used to automatically close the LCD screen when answering the phone to save power.