Research And Design Of Fraunhofer Diffraction Instrument Base On The Embedded Linux Platform

This paper gives a brief dissusion on the primary research and development of the Fraunhofer diffraction experiment instrument which based on the embedded Linux operating system. The chip this system adopted is S3C2410, which of ARM9 series, provided by Samsung Electronics Company. And the operating system this apparetus applied is Embedded Linux, which is an open-resource, free operating system. Based on this OS, the system realized the function of real-time display of Fraunhofer diffraction figure in the LCD and real-time analysis of experiment data; moreover, it can display the teaching pictures, which pre-stored in the flash.As to the hardware of the system, the main CPU is the S3C2410, which is a powerful MPU integrated ARM920T kernel within. This CPU provides multiple functions, low power-consumption and high performance while low price. What's more, the S3C2410 schematic diagram, which offered by Samsung Electronic in the authoritative web site, provided great convenience in the hardware designation.Since this CPU doesn't integrate RAM and flash within the chip, expanded flash and RAM are indispensable. This system expands a slice of 64M NAND flash and two slices of 32M SDRAM. The entire circuit board is a six-layer PCB, and integrates the peripherals interfaces on it: the LCD interface, the touchpanel interface, the stepmotor interface, the light intensity probe interface, and so on. What's more, this system added a 10M/100M adapetive Ethernet interface chip AX88796, thus in the future upgrade it can expand the networking capabilities. As to the touchscreen interface, although the S3C2410 intergrated touchscreen control unit on chip, it didn't used, a dedicated touchscreen drive chip ADS7843, which produced by Burr-Brown Corporation, is added to replace the onboard control unit. Much performance enhancement is brought due to this hardware improvement; for example, the burden of the CPU is alleviated. And what's more important, the conversion precision and comversion rate were greatly enhanced.The designation of the light intensity probe is simpler to the main board. In this part, an intensity-frequency conversion chip was applied to replace the original design project, thus, the light intensity was converted to square wave of different frequency, and the CPU could count the frequency precisely. Finaly, according to the correspondence between light and intensity, the intensity of light could be calculated acculately, and displayed on the LCD displayer.The Embedded Linux was selected as the operating system for this apparatus. The Linux kernel version was 2.6.14. During the whole development, the transplantation of the linux to the S3C2410 CPU was completed successfully, and the development of some applicaton programs was also completed. The transplantation was a complicated process, quite a lot of time was spent in this step. After the transplantation of the kernel 2.6.14, the transplantation of CRAMFS file system was also accomplished. And the user fraction applied the YAFFS file system. Since the CRAMFS file system is readable only, and the YAFFS is readable and writeable, this design project combines the advantages of both sides. Thus, inadvertently modified to the root file system can be prevented, and the expansion of application function can be implemented easily. In addation to transplantation of kernel and file system, some driver programs are also completed. Such as LCD driver, touchscreen driver, stepmotor driver, etc.In the application program part, two main functions are realized completely. The first, the real-time acquisition of light intensity and calculate & display the light intensity distribution curve. The seond, display the teaching picture on the LCD display panel. In the first module, the precision has been greatly improved due to the application of light-intensity to frequency convereion chip. On the contrary, there are some inherent defects in the original design project of photodiode, such as low precision, valnurable to interference, etc. Besides, as the result of the probe was driven by the stepmotor, the position coordinates of the probe can be calculated accurately through measuring the step angle of the stepmotor. And the light intensity can be sampled at either stepforward or stepretreat, not like the former potentiometers design project, because of the Hysteresis Effect, the potentiometers can be interfered obviously by stepretreat during stepforward, so it can't compatiable with double-direction movement.However, due to the shortage of time, there are still some expected design requirements can't be fully achieved. Such as the USB access, the experimental data still can't be stored to the USB disk. And the teaching video playing requirement also can't be met. All of these unachieved requirements will be taken in into solution in the process of future upgrading.