The MMA7260QT can respond to gravity or constant acceleration due to its capacitive detection principle and mechanism。 When gravity is perpendicular to an axis, its axis output is zero-acceleration and therefore is half the VDD (i。e。, 1。65V for typical 3。3V application)。 When gravity is parallel to an axis and the gravity direction is toward the positive direction of that axis, its axis output is half the VDD plus the selected sensitivity

TABLE I。 THE MMA7260QT OUTPUTS WITH RESPECT TO DIFFERENT SENSOR ORIENTATIONS  (VDD=3。3V, 2G SENSITIVITY)

The gravity response capability of the MMA7260 is useful for accurate tilt sensing with respect to any orthogonal planes。 Assume the φ, ρ and θ are the tilt angles of X-,Y- and Z-axis with respect to horizon, respectively with known accelerations all the three tilt angles follow sinusoidal relationship。

= arcsin( ACC x )

arcsin( ACC y )

arcsin( ACC z  )

The resolution (acceleration changed per degree, i。e。, the slope the sinusoidal curve) for any axis also varies with tilt angles due to the sinusoidal relationship。 Take the x-axis for example, the maximal resolution can be obtained when its tilt φ increases from 0° or 180°, and the minimal resolution occurs at φ approaches 90° or 270°。 Therefore a modified tilt calculation is suggested and is valid and applicable because it combines other axis outputs and therefore a maximal resolution of tilt sensing can be retained across any rotation and orientation with respect to any axis。

The block diagram of the three axis accelerometer MMA7260QT is as shown in the Fig。 6。 The various components of the accelerometer sensor can be known from the block diagram。

Figure 6。   Simplified accelerometer functional diagram

VI。LIQUID CRYSTAL DISPLAY

In 1968, RCA Laboratories developed the first liquid crystal display (LCD)。 Since then, LCD’s have been implemented on almost all types of digital devices, from watches to computer to projection TVs 。LCD’s operate as a light “valve”, blocking light or allowing it to pass through。 An image in an LCD is formed by applying an electric field to alter the chemical properties of each LCC (Liquid Crystal Cell) in the display in order to change a pixel’s light absorption properties as shown in Fig。7。 These LCC’s modify the image produced by the backlight into the screen output requested by the controller。 Through the end output may be in color, the LCC’s are monochrome, and the color is added later through a filtering process。 Modern laptop computer displays can produce 65,536 simultaneous colors at resolution of 800 X 600。摘要本项目工作的目的是为了实现与手势重组轮椅方向控制。本文提出了一种综合性方法来实时检测，跟踪和方向识别，其目的是作为智能轮椅的人机交互界面。本文表明，通过对手势识别加速度计数据的校准和过滤，加速度计可以将手指和手势有效地转化为计算机解释的信号。加速度计可以测量除了重力以外的力所引起的加速度的大小和方向。为了校准加速度计，我们旋转相对于设备重力的敏感轴，并使用所得到的信号作为绝对测量信号。文献综述

关键字  手势识别系统，人机接口，微控制器，接受器，发射器

一、简介

加速度计可以用于有效地将手指和手势翻译成计算机能解释的信号。集成了MEMS加速度计的单芯将会产生一个小到足以适用于指甲的自动化设备。加速度计附连到指尖和手的背面。在手上箭头表示加速度计和其敏感方向的位置。加速度计最灵敏方向是在手的平面。微机电系统（MEMS）是无尺度加速度和压力传感器的使能技术。基于传感器产品MEMS能提供一种感测，处理或控制周围环境的界面。基于MEMS的传感器是一类建立在一个芯片上非常小的电子和机械部件的设备。基于MEMS传感器也是汽车电子，医疗设备，硬盘驱动器，计算机外围设备，无线设备和智能便携式电子产品重要的组成部分，例如手机和PDAs都有使用MEMS的传感器。MEMS技术提供了以下优点：成本效益搞，功耗低，小型化，高性能和集成。功能可以集成在相同的硅或在同一包中，这减少了元件数量，有助于降低总成本。