基于单片机的电子换号牌的设计

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Nature kind of odor tens of thousands, even professionals specializing in odor identification work is often recognition errors.Keywords: electronic nose computer technology developed olfactory organs physiological reaction Customs security monitoring neural networks odor sensor identification infrared sensorIntroduction: The electronic nose developed a high-tech products is simulated animal olfactory organ, scientists are still not all clear principle of the animals sense of smell. However, with the development of science and technology, more authoritative some universities in the world have developed electronic nose has a wide range of applications, most notably to the number of the University of Hamburg, Germany, has absolute authority in the sensor field in the world today. Electronic nose is the response pattern to identify the odor of the gas sensor array electronic systems, it can be in a few hours, days or even a few months time within a continuous, real-time monitoring of the specific location of the odor condition. Identifying odor main mechanism of the electronic nose is that each sensor in the array has a different sensitivity of the measured gas. The core of the device of the electronic nose gas sensor. Gas sensors based on the principle of different type of metal oxide, electrochemical, and conductive polymer type, quality, photo-ionization type can be divided into many types. Currently the most widely used is a metal oxide.How it works: Electronic nose is mainly composed of three parts of a gas sensor array, signal pre-processing and pattern recognition. Presented in front of an active material of the sensor, an odor sensor chemical input is converted into an electrical signal by a plurality of sensor response to an odor they constitute the sensor array to the odor of the response spectrum. Obviously, the various chemical components in the odor sensitive materials play a role in this response spectrum for a broad spectrum of odor response spectrum. To achieve the odor qualitative or quantitative analysis, the sensor signal must be appropriate pretreatment (to eliminate noise, feature extraction, signal amplification, etc.), using a suitable pattern recognition analysis method for processing thereof. Theoretically, each odor will have its characteristic response spectrum, according to its characteristic response spectrum can distinguish between small same odor. While gas sensors constituting the array to measure the cross-sensitivity of a variety of gases, by a suitable analytical method, the mixed gas analysis. The electronic nose is the use of various gas sensing device has a response to this characteristic but different from each other, with the data processing methods to identify a variety of odor, odor quality analysis and evaluation of complex component gases. The main mechanism of the electronic nose identify each sensor in the array has a different sensitivity of the measured gas, e.g., high response One gas may be generated on a sensor, while the other sensor is a low response; Similarly, the 2nd gas generating high response of the sensor is not sensitive on the 1st gas and, ultimately, the entire sensor array response pattern is different for different gases, it is this difference, to enable the system to identify a gas according to the response of the sensor pattern. Electronic nose can be summarized as follows: the sensor array - the signal preprocessing - neural networks and a variety of algorithms - computer identification (gas qualitative and quantitative analysis). Functionally speaking, the gas sensor array is equivalent to the biological olfactory system in a large number of olfactory receptor cells, neural network and the computer to recognize the biological equivalent of the brain, the rest is the equivalent of the olfactory nerve signal transduction system. For example, the measurement of the metal oxide semiconductor (MOS) gas sensor in response to the schematic diagram of the voltage signal. MOS gas sensor is usually before the test shall be heated to 2500 (or higher) in order to work properly. After the chemical reaction occurs in the testing process, the MOS gas sensor and the sample gas / odor, will change its own gas sensitive film conductivity and resistance values, leading to a terminal voltage of a sampling resistor in series thereto is changed. Due to sampling resistor is fixed, so the immediate extraction of the end of the sampling resistor voltage signal voltage MOS gas sensor response curve. 图1Features:Electronic nose response time, speed detection, unlike other instruments, such as the gas chromatography sensors, high-performance liquid chromatography sensor need complex pretreatment process; measuring a wide range of assessment, it can detect a variety of different types of food; and to avoid human error, good repeatability; can detect some of the human nose can not detect the gas, such as poison gas or some irritant gases, which in many areas, especially in the food industry plays an increasingly important role. And graphical cognitive equipment to help its specificity greatly enhance the development of sensor materials also contributed to the improvement of its repetitive, and with the improvement of biochips, biotechnology development and integration technology, and some nanomaterials The application of electronic nose will have broad application prospects. Many different types of the electronic nose, the typical working program that is: 1) Sensor initialization: using a vacuum pump to the air sampling lessons to small containers fitted with the electronic sensor array chamber; 2) Determination of the sample and data analysis: sampling operation unit the initialization of the sensor array is exposed to the odor body, when the contact with the surface of the active material of the volatile compounds (VOC) and the sensor (ultrasonic sensor), to produce the transient response. Such a response is recorded and transmitted to the signal processing unit for analysis, and stored in the database of a large number of VOC pattern comparison, identification, and to determine the type of odor; 3) cleaning the sensor: measured after the sample is finished, use of alcohol vapor flush . The sensor surface of the active material, the odor removal measured Bi mixture. In enter new measurement prior to the next round, the sensor still implement initialization (that is, between the work again, each sensor are required dry air or some other reference gas cleaning to meet the benchmarks). The measured odor effect of time is called the response time and the purge process and the reference gas role of the sensor array used in the initialization process time is called the recovery time.The electronic nose system consists of two parts: information acquisition the terminal (Acquisition terminal) and information processing terminal (processing terminal). 1) collection terminal is responsible for collecting the signal voltage of the MOS gas sensor array processing terminal via a handheld computer (PDA) to complete the data analysis and processing. Two terminal data exchanged by the two wireless module. Collection terminal consists of three major components: sampling systems, electrical systems, as well as the sensor array. The sampling system consists of the the gas sensor cavity, micro plow pump and three-way solenoid valve. Circuit system consists of the following functional modules and power: the microcontroller, ADC module, DAC conditioning modules, memory modules, wireless modules and lithium battery. The sensor cavity is placed with the sensor array consisting of eight commercial TGS gas sensor. The work of energy consumption of the entire collection terminal in 6W about, in the case of the lithium battery with a capacity of 3800Amh powered, it is possible to work continuously 3.2h. Collection software on the terminal is under in Keil uVision2 development environment with C language, writing good source through the RS232 serial burn to STC89C516KD + microcontroller. 2) processing terminal by a wireless module, microcontroller, RS232 serial port to USB interface module (RS232 to USB), and PDA. Wireless module with microcontroller interface design circuit with the collection terminal. Because on PDA USB interface, it is necessary to design RS232 serial to USB interface circuit to complete the exchange of data between the MCU and PDAs. The electronic nose system software is divided into two parts. The software is based on processing terminal LabVIEW71 (NationalInstrumentation, USA) platform developed on a PDA (WindowsXP system).Electronic nose in a complete test process, have to go through four stages; ground state phase sampling stage, holding phase and the recovery phase. Stage in the base state, the three-way solenoid valve is switched to the air passage, and a voltage signal of the sensor array to a horizontal baseline. To be a three-way solenoid valve is switched to the sample gas channel into the sampling stage, the sensor array response, a few seconds after the voltage signal value rose to a peak and then stabilized, to be close to equilibrium, the system enters the holding phase, three-way solenoid valve remains constant sample gas channel. The last to enter the recovery phase, three-way solenoid valve is switched back to the air channel, rapid decline in the response curve of the sensor array, until it is restored to the baseline position. The time value of the four stages of the testing process before the start of the test, you must first set on a PDA: the ground state time, sampling time, hold time and recovery time. Then Start command, the system began to test issued by the PDA. Collection terminal after receiving the order, the internal microcontroller in accordance with the instructions, timer to control the time of the four stages. First, the microcontroller will control the heating voltage of DAC conditioning module output is used to heat the sensor array, and then control the signal voltage of the ADC module acquisition sensor array and choose to get the data saved to the memory module, or directly to the receiver by the wireless module feedback PDA to do the analysis and processing. After the data acquisition is completed, PDA sends end command, the system stops working. During the next round of testing is required before the PDA issue a reset command to make the system cleared before a new round of tests. In addition, in the process of testing, you can issue commands through the PDA miniature air pump and three-way electronic valve control switch. After the test is stopped, the data of the sensor array can be read through the open instruction to obtain before and response curves.Statistical methods:Principal component analysis (PCA)Principal component analysis refers to several variables by linear transformation to elect a fewer number of important variables of multivariate statistical analysis method, also known as principal component analysis; It is a statistical analysis method to grasp the principal contradiction of things, you can parse out the main influencing factors from diverse things, to reveal the nature of things, simplify complex problems. PCA as a linear feature extraction technology, designed to exploit data dimensionality reduction idea that the calculation of the main components and high-dimensional data is projected onto a lower-dimensional space, multi-indicators into a few indicators, so as much as possible to show the information contained in the original data. PCA in electronic noses for an objective analysis of the differences between the samples.cluster analysis (CA)Cluster analysis is a kind of subjects were divided into relatively homogeneous groups of statistical analysis techniques. From a statistical point of view, the cluster analysis is a way to simplify the data through data modeling. CA is classified based on the relationship between the number of the individual or variable the objectivity strong, but various clustering methods can only be achieved under certain conditions the local optimum; whether the final result of the clustering to set up, take identification of experts.Discriminant factor analysis (DFA)The judgment factor analysis is a statistical method to determine the individual category. Observations according to the known classes of two or more samples to determine one or more linear discriminant function discriminant index, then another body to determine which category the discriminant function based on discrimination index. DFA according to the results of the standard sample used for electronic noses to identify blind. By re-combination of sensor data to optimize the differentiated, or through the sensor optimized selection, i.e. removal of the sensor, no contribution or a small contribution to improve the recognition capability, its purpose is to bring the group distance between the difference within a maximum while ensuring group minimum.Artificial Neural Network (ANN)The artificial neural network is a by imitate human or animal neural network behavioral characteristics, mathematical model of distributed parallel information processing. This network relies on a system of complex procedures, by adjusting the the internal large number of interconnected relationships between nodes, so as to achieve the purpose of processing information. ANN provided in advance a number of mutually corresponding input data - output data, analysis, grasp the potential between the law, and ultimately with a new input data According to these laws, to derive output, this The learning process of analysis is called training. The aforementioned methods, ANN is usually considered to be a promising approach, and its features and benefits mainly in three aspects: with self-learning and adaptive function; associative memory function; with high-speed to find the optimal solution capacity. In addition, it is able to solve nonlinear problems better than the traditional statistical methods in dealing with noise and drift. Currently, many artificial neural network is used for processing the signal of the sensor array, such as BP neural network, radial basis neural networks, fuzzy neural networks, self-organizing network.图2Research progress:In 1964, Wilkens and Hatman use of gas on the electrode, the oxidation-reduction reaction olfactory process electronic analog, which is the earliest reports on the electronic nose. 1965, Buck et al the use of changes in the conductance of a metal and a semiconductor gas measurement, Dravieks then using the change in contact potential measurements of the gas. However, as the gas classification with the concept of intelligent chemical sensor arrays until 1982 by the University of Warwick, UK Persuad et al, their electronic nose system consists of two parts of the gas sensor array and pattern recognition system. The sensor array part of the mountain three semiconductor gas sensor. This simple system can distinguish between the brain, according to the tree rose oil, clove oil, volatile chemical substances for dental odor. In the next five years, the electronic nose research and did not cause extensive attention in the international academic community. 1987, held at the University of Warwick, UK 8th Annual Meeting of the European chemical sensing research organization is the turning point of the study of the electronic nose. At this meeting, Gardner led by the University of Warwick in gas sensing sensing research team published a paper sensor in gas measurement parties and applications, focusing on the concept of pattern recognition, caused academia extensive interest. In 1989, the North Atlantic Treaty Organization held a special chemical sensor information processing symposium, dedicated to artificial olfactory system design of these two topics. In August 1991, the North Atlantic Treaty Organization was held in Iceland thematic sessions of the first electronic nose. The electronic nose Since then rapid development. 1994, Gardne: a review article on the electronic nose, formally proposed the concept of electronic nose, marking the electronic nose technology into the mature stage of development. Since 1994, after more than ten years of development, the electronic nose research has made rapid progress. For the study of the electronic nose mainly in the side of the sensor and electronic nose hardware design, pattern recognition theory, the electronic nose in food, agriculture, pharmaceutical, bio-field applications, electronic nose, and biological systems while. The hardware design of the sensor and the electronic nose and electronic nose applications in the field of food and agriculture is a hot spot in the study of the electronic nose. Crewe town in Cheshire, England company successfully developed an electronic nose, the tests showed that the patient skin wound bacteria can sniff out the erosion remind doctors to take appropriate measures in a timely manner. His study of the electronic nose is a matrix composed of 32 different organic polymer sensor, very sensitive to the smell of various volatile compound, the compound is different, the reaction is different. Typically, bacterial growth will be issued chemical odor the electronic nose contact with the odor, each sensor resistance will change. Format Since each sensor corresponding to a different kind of chemical substances, composed of 32 kinds of the same change in resistance would respectively represent the fingerprint of the different odors. The tests showed that the electronic nose can be found if there is the presence of bacteria only need a few hours. In the past, using the methods of the laboratory tests, usually 1-3 days to get the results. The gas sensors in the system of electronic nose, the gas sensor is the perceived odor of the basic unit, are also key factors. However, due to the strong specificity of the gas sensor, which makes the detection of the gas mixture or the presence of interfering gases, the single sensor is difficult to obtain a higher accuracy of detection and identification of. Therefore, the portion of the odor perception of the electronic nose often use a plurality of a gas sensor having a different selectivity, according to a certain array combination, the use of the cross-sensitivity of a variety of gases, the different odor molecules in its role of the surface is converted to a convenient calculate the time-related physical signal group, can be measured to achieve the analysis of the mixed gas. At present, the main types of electronic nose sensors conductive sensors, piezo sensors,