Microcomputer automation of a microwave spectrometer

Abstract

Since the advent of microcomputers the trend in laboratory data acquisition has been toward automatic control of the experiments, digitization of analog information and computerized data reduction. In a computer automated spectrometer, in addition to the several advantages, one is able to use new techniques in digital data manipulation to improve the quality of the spectral data. In this paper, the interfacing of an Hewlett-Packard Model 8460A microwave spectrometer with an Intel 8085 MPU based microcomputer is discussed. The two important objectives of this work were to enable a relatively inexperienced operator to obtain the data by running the experiment and to take advantage of the power of digital techniques available. The microcomputer has 64K bytes of dynamic random access memory. Among the other accessories are a dual floppy disk drive, a decwriter and a video monitor. The data acquisition is accomplished using AltairT'M'8800 Analog to Digital/ Digital to Analog (AD/DA) converter. The hardware interface with the microwave spectrometer system is done through a programmable I/0 board, using two Intel 8255 I/O chips. The components of a microwave spectrometer and its operation will be discussed briefly. Of the various components, the Sweep Control unit is of particular importance. This unit accepts the frequency command from the computer in BCD code and processes it to select a specific frequency. The corresponding analog output from the spectrometer is digitized and stored in a floppy diskette. To display this spectral data, the microcomputer is also interfaced with an X-Y plotter. The algorithm used in developing the software for the data acquisition from the spectrometer is given below. i. START; 2. Set the experimental conditions; 3. Initialize the I/O ports for output; 4. Initialize the Sweep Control;