Design And Realization Of Positioning System On LCD Screen Based On Ultrasonic Technology

The positioning system working on the surface of a LCD screen is used in modern paperless office. The positioning system use LCD as the background to write and operate, and it can display the track of writing and the results of operation, improving the exchange. Positioning systems in market use infrared technology, and the positioning accuracy is not very good. Positioning system LCD screen is designed and based on ultrasonic in order to improve the positioning accuracy, finishing the written function.The ultrasonic localization technology can be applied in mobile robot, virtual reality (VR), smart home, consumer electronics and other application fields with its advantages such as low price, minimal infrastructure, low maintenance cost and less electromagnetic pollution. However, ultrasound signal is sensitive to the external environment, especially temperature, making ultrasonic positioning technology poor in positioning accuracy. In this paper, a microphone is used as a receive sensor in hardware circuit, and complete the LCD screen positioning system hardware design.Precise positioning of Ultrasonic positioning system is based on accuracy measurement of the time of flight. The threshold and cross-correlation method are the common methods for time of flight this measurements. The inherent drawback of threshold method is the integer signal periods errors. The localization system based on threshold method can not achieve high resolution because of the existence of integer signal periods errors. The cross-correlation method is the optimal method. In this method the received ultrasonic pulse is assumed to be time shifted, amplitude scaled and noise corrupted replica of reference signal. But in the actual system, AD sampling rate limit the methods, whether use the correlation algorithm is determine by the accuracy and computational complexity in practice. It use the sliding window method to reduce computational complexity and three-point parabola fitting joint to improve the accuracy of estimates.The main content of the paper are as follows:In first chapter, there are four positioning Methods on the surface of LCD screen. Analysis positioning characteristics of optical, resistive, SAW and capacitive touch-screen are discussed. For the shortages of these touch-screens positioning, we use ultrasonic location to design a positioning system. An overview of the basic principles of positioning system, the method and difficulties of positioning system is given. Identify the main research content of this article.In chapter two, the introduction and the analysis of the development and the present situations of ultrasonic localization technology are summarized. The chapter shows the analysis of the principles of ultrasound, the realization of methods and the impact of positioning accuracy.It is hardware design of positioning system on LCD screen in chapter three. First of all, the paper analyses the characteristics of the ultrasonic signal spread on surface of the LCD screen. The paper show the design of AD sampling circuit of the infrared signal and ultrasonic signal, the ultrasonic receiver superposition circuit and signal processing circuits, including power supply, oscillator and memory circuits. Finally, there is communication with the host computer circuit - USB circuit.In chapter four, it shows the functions and programming of positioning system. Mainly content are the procedure for hardware, sampling, extraction of time of flight and Communication functions. This chapter introduce the details about the procedures for DSP and system process as well as the positioning algorithm, focusing on analysis of related algorithms, using the sliding window method to reduce computational complexity and three-point parabola algorithm to improve the accuracy.Chapter five is about system debugging, including the debugging tools, testing methods and testing process, also analyze debugging problems during the process of hardware and software design and find out the solutions, modify system hardware and related programming, and show the rusult.In chapter six, a brief summary of this dissertation is given with the future expected work.The mainly work of this dissertation as follows:Positioning system on LCD screen structure and function are designed on the whole.Ultrasonic signal is seriously affected by the temperature of the liquid crystal surface, the effect of Multi-path make it even worse, and can not be determined by the characteristics of ultrasonic signals, and then does not recognize the signal. This paper analyzes characteristics of ultrasound signal on the surface of LCD, use the microphone sensors as the ultrasonic signal receiver to design receive circuit.Learning and exploring how to design the hardware of positioning systems using TMS320VC5502DSP. Design the hardware platform of the ultrasound signal receiving and processing circuitry.Although implementation of the assembly language is high efficiency, it is poor in readability and portability and not conducive to upgrades and development of system hardware and software. Using the C language to complete the hardware design is necessary.After analysis the shape and the characteristics of the ultrasonic received, the signal algorithm is designed. Firstly, using the rapid window function find the fuzzy location, then determine the signal arrival time through the correlation algorithm. Finally, improve the measurement accuracy through the three-point parabolic fitting algorithm.Test the hardware and software.The innovation ideas of this dissertation focus on the three aspects as follows:Design receiving circuit using a microphone sensor as the signal receiver to solve the problem of signal overlap serious and reduce the impact of temperatureTo resolve problem of the liquid surface temperature and infrared wave interference, give up the threshold method to determine the time of infrared sync signal arriving, design AD sampling the receiving pulse of infrared signal. Judge the arrival time of infrared signal by measuring the infrared pulse amplitude and duration Algorithm of ultrasonic location is composed of the rapid window function, the correlation algorithm and parabolic fitting algorithm.