CSHIA Micro Lesson | Hyman Zeng Yonggang: How to design and apply smart sensors?
Source: Hyman Technology Release time: 2019-11-27 Clicks:
With the development of the Internet of Things technology, the application of smart homes is also becoming more and more popular. As the nerve endings of the smart home, smart sensors play a decisive role in the smart home experience. Without sensing devices, smart homes cannot be truly intelligent. The application fields of smart sensors are very wide, and their coverage includes smart manufacturing, smart cities, smart security, smart home, smart transportation, smart medical, etc.
The smart sensor concept was first proposed by NASA during the development of the spacecraft, and was formed in 1979. The IEEE Association refers to sensors that can provide a controlled or to-be-perceived size and that can typically simplify their integration in a network environment as smart sensors. Intelligent sensors are a new type of sensors with microprocessors that have information detection, information memory, logic analysis and judgment functions, and communication and management functions. Smart sensors have the ability to automatically zero, calibrate, compensate, and collect data. Its ability determines that the smart sensor also has higher accuracy and resolution, higher stability and reliability, and better adaptability. 温湿度传感器、气体传感器、烟雾传感器、压力传感器、加速度传感器、光照度传感器，人体移动传感器等等。 At present, smart sensors commonly used in smart homes include temperature and humidity sensors, gas sensors, smoke sensors, pressure sensors, acceleration sensors, light intensity sensors, human movement sensors, and so on.
The development trend of smart sensors
Moving towards high precision With the development of science and technology, the accuracy of existing sensors can no longer meet the requirements, and the requirements for sensor accuracy are getting higher and higher.
Moving towards high reliability The reliability of the sensor directly affects the accuracy of the data and the user experience. High-reliability sensors need to be able to work stably for a long time under anti-interference and adapt to changes in different temperature and humidity environments.
Move towards miniaturization At present, the functions of various control instruments are getting stronger and stronger, and the smaller the volume of each component is, the better, so the smaller the volume of the sensor itself is, the better.
Moving towards micropower At present, many smart sensors are powered by batteries. The reduction in power consumption means that the battery's service life will be longer, and users do not need to replace the battery frequently, which improves the user's experience. In the past, the smoke alarm required replacing the battery once a year. With the reduction of power consumption, the current battery of a CR123A smoke alarm can be used for more than 10 years. Traditional sensors can only detect a single type of physical quantity. Today's smart sensors integrate multiple physical sensors and can simultaneously detect multiple physical quantities. For example, one of our smart sensors has both temperature and humidity, illumination, acceleration, and human movement Detection, users only need to purchase a smart sensor to achieve detection of multiple physical quantities. Networking is an important direction for the development of sensors, and the role and advantages of networks are gradually emerging. Network sensors will definitely promote the development of electronic technology. What problems can smart sensors solve in smart home systems? ：在欧美发达国家，目前安防仍然是刚需，政府立法规定住宅必须安装安防设备，例如烟雾传感器、一氧化碳传感器、防盗报警传感器等，传统的安防产品，只有人在家里的时候能够知道有警情发生，如果不在现场就收不到报警信号。 1. Real-time data : In developed countries in Europe and the United States, security is still just needed. Government legislation requires that residential buildings must be equipped with security equipment, such as smoke sensors, carbon monoxide sensors, burglar alarm sensors, etc. Traditional security products can only be used when people are at home. Know that there is a police situation, if you are not on site, you will not receive an alarm signal. In the intelligent era, the data of each of our security sensors can be transmitted to the cloud platform and user's APP through the Internet of Things technology for the first time. Keep abreast of home safety in real time and avoid unnecessary losses. ：智能家居想要实现“自动化场景”离不开传感器的数据信息，这个时候传感器的数据就可以作为“自动化场景”的触发条件。 2. Linkage trigger : The smart home wants to realize the "automated scenario" without the data information of the sensor. At this time, the sensor data can be used as the trigger condition of the "automated scenario". For example: we want to turn on the lights automatically when there is someone, and turn off the lights automatically when there is no one. At this time we will use human infrared sensors; when the weather is hot, automatically turn on the air conditioner, you need the data of temperature and humidity sensors. When the gas leaks, the valve is automatically closed and a gas sensor is used. ，并将这些数据发送给AI进行分析和处理。 3. Provide a large amount of environmental data for AIoT , and send this data to AI for analysis and processing. This data is also an important feed for AI for deep learning, helping AI to become smarter and make smarter decisions. In summary, the use of smart sensors is very wide, it can monitor all the conditions in the home or hidden dangers, remind users when necessary or trigger measures to mitigate hidden dangers. With the rapid development of smart homes, more and more home products are becoming intelligent, providing users with a safe and convenient life experience. These smart sensors have a great auxiliary role.
How to design a smart sensor device that is popular in the market? 1. First of all, it should be a complete definition of the product. Before designing a smart sensor, we must make clear the audience, function, appearance, wireless communication method, power supply method, battery life, cost, etc. of this product. 2. The appearance determines the success of a product. The appearance is the first impression left to the user. The user cannot see the intrinsic quality of the product at a glance, but can see whether the appearance is novel and the workmanship is fine. Overall positioning. The most important task of appearance design is to control the needs of the market, grasp the psychology of users, and design the appearance of products that most customers can accept. The appearance design of the smart sensor should be simple, small, and modern, and it doesn't need to be too fancy in design. It should be able to be integrated into the decoration of modern homes. 3. The stability of the performance of smart sensors is very important, especially for smart security sensors. The principle of smart sensors basically uses sensors to detect different physical signals and then convert them into electrical signals. When the electrical signals are weak, signal amplification is required. Then, it is sent to the MCU for calculation and processing. For data that meets the alarm or needs to be reported, it is reported to the gateway or cloud platform through wireless communication technology. The stability of smart sensors is not good, and they will be susceptible to environmental interference and false positives or false negatives. For example, human body infrared sensors report data of someone when there is no one. Conversely, when someone passes through the detection area, the Report someone's data, which will seriously affect the user experience.
What are the factors that cause the stability of smart sensors to be poor? 1. Selection of key components. The key piece is one of the main factors affecting the performance of smart sensors. The key component of a human body sensor is a pyroelectric infrared sensor. In the selection process, we must pay attention to some of its key indicators. For example, key indicators such as detection angle, detection distance, anti-RF interference performance, and signal-to-noise ratio, and then the choice of Fresnel lens. When choosing a Fresnel lens, we should pay attention to its focal length, detection angle and detection range And other parameters, if the Fresnel lens is not selected properly, the sensitivity of the human sensor will be greatly reduced. ，很多时候，因为关键器件的选型不合适，导致探测灵敏度下降，这个时候就会调高硬件放大电路的放大倍数，放大倍数调的太高时，干扰信号也被放大，就会导致传感器误报。 2. The design of the hardware circuit and PCB LAYOUT . Many times, because the key components are not selected properly, the detection sensitivity is reduced. At this time, the amplification of the hardware amplifier circuit will be increased. It is also amplified, which will cause false alarms by the sensor. When the PCB layout is unreasonable, for example, the layout of analog circuits and digital circuits is unreasonable, and the layout of signal amplifier circuits is unreasonable, it will cause external RF signals to enter the amplifier, leading to product false alarms. 3. Signal processing. There are some cheaper human sensors on the market, and their signal processing is too simple. After the sensor signals are amplified, a simple comparison is performed through a comparator. If a fixed threshold is exceeded, the alarm will be reported. Such a treatment method is very easy to produce false positives. The method adopted by our human body infrared sensor is that after the signal of the sensor is amplified, it is sent to the MCU for AD sampling, and the sampled signals are compared. The software processing uses dynamic threshold adjustment, automatic temperature compensation, energy analysis and other algorithms. It can accurately identify the movement of the human body, has strong resistance to radio frequency interference and light interference, and achieves high detection sensitivity without false positives and false negatives. 4. Selection of communication protocol. Now more and more smart homes adopt wireless communication methods. At present, wireless communication technologies include RF315, 433, NB-IoT, LORA, Wi-Fi, BLE, Zigbee and so on. Faced with many wireless communication technologies, each has its own advantages and disadvantages, how should we choose? There are cost considerations, power consumption considerations, security considerations, wall penetration effects, and interoperability with other hardware. 具有低成本、低功耗、传输距离远、穿墙能力强、频点单一容易受同频干扰，网络通讯安全性低，不能够自组网等特点，应用在电子玩具、工业控制、无线数据采集等领域。 RF315, 433: low cost, low power consumption, long transmission distance, strong wall-penetrating ability, single frequency point, easy to be interfered by the same frequency, low network communication security, not capable of self-organizing network, etc., applied to electronic toys, industrial Control, wireless data acquisition, etc. 烟感、水表、气表、井盖、路灯和停车等领域应用，实现物联网通讯。 NB-IoT, LORA: It has the characteristics of low power consumption, long distance, etc., and is used in the management of public facilities, such as: smoke detection, water meters, gas meters, manhole covers, street lights and parking, etc., to achieve the Internet of Things communication. Wi-Fi has simple operation, fast data transmission, high power consumption, and few devices that can be accessed by one router. It is widely used in smart single products and smart home appliances. BLE is Bluetooth low energy, which has the characteristics of low power consumption, low cost, short distance, and convenient connection with mobile phones. Based on the low power consumption characteristics, BLE is widely used in wearable devices, health monitoring devices and other products. Starting from the Bluetooth 4.1 protocol, Bluetooth mesh products have the characteristics of ad hoc networking, but Bluetooth mesh is still in the technology accumulation period.
Zigbee is a low-power LAN protocol based on the IEEE 802.15.4 standard. It is an open wireless mesh network technology with low power consumption, low cost, ad hoc networking, high security, interconnection and interoperability, strong interoperability, and network nodes. Large number of features, so Zigbee is widely used in the field of smart home. At present, more than 3,000 products worldwide have passed Zigbee 3.0 certification.
Common problems of smart sensors in landing applications AC供电的产品都是直接插到220V插座上，对于智能安防传感器，在安装时还是有些需要特别要注意的。 Most of the current smart sensors are relatively simple to install. Battery-powered products are equipped with 3M glue and can be directly installed on the wall. AC-powered products are plugged directly into 220V sockets. For smart security sensors, there is still some need for Special attention. For example, when installing a human body infrared sensor, you should avoid installing it near a curtain, a place that is suddenly cold or hot, otherwise a false alarm will occur, which is determined by the principle of the human body infrared sensor. 如果使用的是液化石油气，安装的位置就需要选择比泄漏源低的位置，因为液化石油气的比重比空气重，在气体泄漏的时候会往下沉。 For smart gas alarms, you need to know the type of gas used in the kitchen during installation. If it is natural gas, the installation location should be selected higher than the source of the leak, because natural gas is lighter than air, and it will float upward when leaked; If LPG is used, the installation location needs to be selected lower than the leak source, because the specific gravity of LPG is heavier than air, and it will sink when the gas leaks. Most of the current smoke alarms use photoelectric smoke sensors. Its principle is to detect small particles of smoke and identify smoke alarms through the reflected signals of smoke particles. When installing, you should pay attention not to install in places with large dust. Large places, such as furniture factories, kitchens and other places. When installing, you should also consider the signal problem. Take Zigbee's smart home for example. If our battery-powered smart sensor is far away from the repeater or gateway and is at the critical point of communication distance, when the sensor wakes up every time When you come, you ca n’t send data to the gateway in a very short time. It takes a certain amount of time to try to communicate with the gateway. This will speed up the use of the battery. Normally, the battery can be used for 1 year. When installed at the signal critical point The battery may only be used for half a year. In this state, the gateway often cannot receive the sensor's signal, causing the sensor to go offline. 智能开关，智能插座等AC供电的产品，具体要参考设备厂家的说明书了解这些设备是否带中继功能。 When installing, you need to choose a suitable location for installation according to the communication distance recommended by the equipment manufacturer. When the installation location is far from the gateway, you need to install a device with a relay function in the middle position, such as: smart switches, smart sockets For AC-powered products, please refer to the equipment manufacturer's instructions to find out whether these devices have a relay function.
Product selection is also important At present, there are many smart home products on the market, and the price and quality are also uneven. How should we choose? 1. For smart sensors, stability is the key. How to judge the stability of the product? 其次就是了解关于这些产品的法律法规，是否有通过国家的一些关于产品质量的强制性认证。 The stability of any product requires a process of technological accumulation. In the choice of brands, we must choose companies that have developed in this field for many years and have relatively strong technical strength. Secondly, we must understand the laws and regulations on these products and whether they have passed some of the countries. Compulsory certification of product quality. There is also the reputation of the brand's products in the industry. If these aspects are done well, the stability of the product will not be a problem. 2. The choice of wireless communication protocols. The Zigbee protocol is currently used more in the field of smart homes. We also need to pay attention when selecting Zigbee smart sensors, and try to choose products that have passed Zigbee Alliance technology certification. Authentication can be queried through the official website of the Zigbee Alliance. 没有通过认证的产品可能存在兼容性的问题，会出现网关不能识别，或者部分功能不能使用，容易离线等问题。 The advantages of choosing a Zigbee-certified product are interoperability, good interoperability, and high security; products that do not pass the certification may have compatibility problems, and the gateway may not be identified, or some functions may not be available, and it is easy to go offline. 3. Select energy-saving and environment-friendly products. Energy saving and environmental protection have become the key words, promoting energy saving to become a consumption trend and industry trend, and various industries are also advocating "energy saving" and "environmental protection". As a smart home manufacturer, providing users with both easy-to-use and energy-saving products cannot be ignored. Smart home control systems based on the Internet of Things technology and automation technology, energy saving and environmental protection functions are most prominent in lighting energy saving, and can be through various timing event management, induction control functions, brightness sensors, human infrared sensors, automatic detection of light brightness and other cores Means to achieve energy-saving lighting. For battery-powered products, the battery life must be considered. The battery life must be at least 1 year. The battery cannot be replaced frequently, which affects the user experience and the pollution to the environment.
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