The Research Of Portable Spectrometer Based On ARM7TDMI-S

Analyzing the chemistry composition and the structure of material bymaking use of the characteristic spectrum of the marerial's radiation orabsorbance is the basic contents in the spectrum analysis. And a spectrometeris the essential instrument in the sectrum analysis, whose basic function ismeasuring the material's spectrum composition including wave-length,strength of the spectrum etc.. The grating spectrometer is widely used becauseit has advantages of even color-spread, high resolution, concentrativeenergy,spreaded spectrum-scope etc.. The CCD has a series of advantages suchas small size, light weight, low power-consume,good linearity,low noise, bigdynamic scope, broad scope of spectrum response, long life, span real-timedelivering and self-scan that make its application more and more extensive.The measurement system constituted by the CCD grating spectrometer and thecomputer's data collected system have the function of sampling, saving,delivering and handling the spectrum information, these functions make thespectrum's measurement numeric. It will be widely applicated in the realm ofthe spectrum measurement.In this paper, a Portable spectrometer based on ARM7TDMI-S isdesigned. The CCD—ilx511 which has high sensitivity, designed by SONYcompany is adopted to do the light-electricity conversion job. The ray sendedout by the light source fall on the grating surface through the narrow gap andwas spreaded, then the spreaded ray become imaging in the CCD, the CCDsample outputs is analog voltage, then through a interface circuit the analogvoltage is converted to be digital signal by the A/D conversion. Then throughthe RS-232 serial port, the digital signal is delivered to the computer andprocessed in the computer, the spectrum diagram is drawed in the computer.Adopting ilx511 can make the size of the optical system smaller so that itcan lower the manufacturing cost and minish the volume of the instrument.It can also reduce CCD's integratiag time to raise the measuring speed of thesystem. each CCD's position is corresponding to the different wave-lengthafter the ray's color is spread, the CCD's output is the video signal of themesured ray, each size of discrete signal is corresponding to the strong or weakof the light intensity and the sequence of the output signal presents thesequence of the light intensity position. The CCD's output is sampled bit by bitby the sample circuit. According to the sample number, we can know thewave-length of the signal, and the amplitude of the signal is the spectrumenergy of that wave-length. So, as long as we sample to the target once, wecan get spectrum distribute curve within a scope of certain wave-length.This thesis adopts the small scaled pack in the circuit design, we gatherARM controller, the CCD image sensor, buffer interface module, A/D transfer,the exterior serial port to connect together to make a bit of circuit board, andso we carried out whole functions within a single board. Doing this not onlyreduced the physical volume of the system, more important it reduced exteriorwalk-line quantity, assuring the security of the system. In the meantime,because the A/D converter is completed in the head, the transfering of digitalsignal lower the noise interrupt of the transmission of the high-speed signal.The external interface adopted serial port method and can connect with thecomputer expediently.As regards the design of application program, we transplanted theoperating system of μC/OS-II to the ARM, bringing the convenience ofcontrolling the mission of performance, adopting multitask adjusted techniqueto ensure the real-time function of the system. So we can put more energies tothe application program, with no need to concern the management of thesystem resources. Doing this shortenned the development period, lowered thedevelopment cost and raised the development efficiency. In the design ofcomputer's application program we adopted Microsoft Visual C++6.0integration and development environment, the function includes initializinginstrument's parameters, reading data from the instrument, handling andsaving spectrum data etc.. Application program adopted the multi-threadingtechnique, the work of reading and processing the spectrum data is completedin the measure threading and the measurement threading can not interfere thecustomer's operation to the main program.The power supply of this circuit adopted AC and DC power supply,which made the system portable.This thesis made light source with the hollow cathode light of differentwave-length, and adjust the relation of CCD pixel serial number p and theincidence wave-length λp, by adjusting we drawed up the two rankpolynomials adjusting formula λ p= -2 E-5p2+0.23p+350.85. Thehot-preparing time is mainly decided by the instrument light source--iodinetungsten light and the hot-preparing time of the power supply module. Bytesting we found that the iodine tungsten light attains a stability after 20 mins.This instrument measures the wave-length scope as 350.0-750.0 nm, thespectrum resolution is 0.21 nms/pixels at the 450.0 nm, the power supplymode is AC and DC power supply and the working current is 150 mA.