| Virtual instrument is a powerful and flexible integrated test, measurement and control system, which is composed of computer technology, application software and modularization hardware. In recent years, Virtual instrument develops rapidly and is broadly applied. As a new bus standard in computer peripheral hardware, USB is adopted and widely used in virtual instruments for its ease of use, true plug and play, power supply from bus, high transmission speed, etc.The purpose of this project is to design and develop a virtual instrument that can test and display semiconductor transistor output characteristics curve, instead of tradition instrument which has being used in labs by now.Based on the analysis of the tradition instrument XJ4810, general configuration and working principle of this virtual instrument were discussed. Firstly, a data acquisition circuit was designed, which is consisted of AD420, DAC702 and AD7701. Then, comparing with different USB control ICs, AN2131 was selected to achieve the control of data acquisition and USB communication. Detailed rules to develop a USB device general purpose drivers were introduced, and the virtual instrument application software was developed basing on LabVIEW. Focus on the method of driver USB device in LabVIEW develop environment, three ways ( I/O, CIN, CLF ) were discussed, and the way of using VISA (Visual Instrument Software Architecture) to communicate with USB device was used that can easily develop instruments driver and application software and improve the applicability of instruments on various operating systems. Finally, source code of firmware was given.The result of experiments proves that virtual semiconductor characteristic curve instrument basing on LabVIEW and USB can run normally. The sample rate is 500 per second, and the total error is less than 2%. |
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