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The working principle of 1D time-of-flight ultrasonic transducer and its application in the smart home appliances(1)

Views:2     Author:Site Editor     Publish Time: 2020-05-21      Origin:Site

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Smart home appliances are home appliance products formed by introducing microprocessors, ultrasonic sensor technologies, and network communication technologies into home appliances. The intelligentization of home appliances should respond automatically according to the surrounding environment without human intervention. This inevitably involves the participation of sensors. This paper compares several distance measurement of ultrasonic distance transducer.
such as infrared tube, proximity sensor, 1D time-of-flight sensor and triangle distance sensor, and specifically introduces the principle of 1D direct time-of-flight sensor and the application of smart TV as an example.
The development of smart homes is already unstoppable, and smart home appliances for the highest proportion in smart homes. Smart home appliances are home appliance products formed by introducing microprocessors, sensor technologies, and network communication technologies into home appliances. They have the ability to automatically make sense the status of home appliances and the service status of home appliances. For example, we can direct the work of household appliances such as sweeping robots and televisions through smart phones and smart speakers.


The intelligentization of home appliances needs to respond automatically according to the surrounding environment without human intervention. Such automatic perception of the surrounding environment will inevitably involve the participation of ultrasonic sensors. The 1D time-of-flight ultrasonic sensors introduced in the past two years have slowly been recognized and applied by major smart home manufacturers.


Comparison and application of several ranging schemes
The commonly used ranging solutions on the market mainly include infrared tube, proximity sensor, 1D time-of-flight sensor and triangular distance sensor. The principles, advantages and disadvantages are as follows:


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Table 1: Comparison of infrared ranging solutions
Infrared tube and infrared proximity sensors are more suitable for distance measurement solutions in smart homes ,such as automatic clamshells and automatic toilet seats, automatic faucets and other application scenarios, because this scene does not require high precision, but high-quality sanitary and automatic faucets are also switching to the 1D time-of-flight ultrasonic sensor solution.
1D time-of-flight 200KHz ultrasonic transducers are more used for obstacle recognition and staircase detection of sweeping robots, proximity detection of smart TVs, proximity lighting of smart lights, eye protection of projectors and auto-focusing functions, 3D smart door locks and other applications scenes.Next, we will introduce the principle of 1D direct time-of-flight ultrasonic sensor and the application of smart TV as an example.


The working principle and advantages of 1D direct time-of-flight ultrasonic sensor
Take the new TMF8801 that can detect the distance of 2cm ~ 2.5m as an example. The internal structure is as follows:


Figure 1: TMF8801 internal structure diagram
The IR laser transmitter (using VCSEL) emits photons through the optical components, and at the same time sends a start signal to the time-to-digital converter (TDC), the photons will be reflected back when they encounter obstacles, and are received by the single-photon avalanche diode at the receiving end of TMF8801 ( SPAD) received, and caused SPAD to avalanche, thus giving TDC a stop signal. TDC calculates the time between the start and stop signals to know the time of flight of the photon to and from. If the speed of light is known, the distance between the object and the ultrasonic wind sensor transducer can be calculated. Distance is a real time flight measurement.


Figure 2: The principle of distance calculation
Advantages of TMF8801 time-of-flight sensor:

  1. Histogram output
    The TMF8801 can directly output histogram data. The histogram is an accurate graphical representation of the data distribution. It is processed by continuously collecting the infrared light reflected by the object and reflecting the distribution of the TDC data, which facilitates the accurate calculation of the distance algorithm.

    `XU_LQEPCWU744K158J


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