TOUCH SCREEN

First computers became more visual, then they took a step further to understand vocal commands and now they have gone a step further and became ‘TOUCHY’, that is skin to screen.

A touchscreen is an easy to use input device that allows users to control PC software and DVD video by touching the display screen. A touch system consists of a touch Sensor that receives the touch input, a Controller, and a Driver. The most commonly used touch technologies are the Capacitive & Resistive systems. The other technologies used in this field are Infrared technology, Near Field Imaging & SAW (surface acoustic wave technology). These technologies are latest in this field but are very much expensive.

The uses of touch systems as Graphical User Interface (GUI) devices for computers continues to grow popularity. Touch systems are used for many applications such as ATM’s, point-of–sale systems, industrial controls, casinos & public kiosks etc. Touch system is basically an alternative for a mouse or keyboard.

The market for touch system is going to be around $2.5 billion by 2004. Various companies involved in development of touch systems mainly are Philips, Samsung etc. Even touch screen mobile phones have been developed by Philips.

INTRODUCTION

A touchscreen is an easy to use input device that  allows users to control PC software and DVD video by touching the display screen. We manufacture and distribute a variety of touch screen related products.

A touch system consists of a touch

Sensor that receives the touch input, a Controller, and a Driver. The touch screen sensor is a clear panel that is designed to fit over a PC. When a screen is touched, the sensor detects the voltage change and passes the signal to the touch screen controller. The controller that reads & translates the sensor input into a conventional bus protocol (Serial, USB) and a software driver which converts the bus information to cursor action as well as providing systems utilities.

As the touch sensor resides between the user and the display while receiving frequent physical input from the user vacuum deposited transparent conductors serve as primary sensing element. Vacuum coated layers can account for a significant fraction of touch system cost. Cost & application parameters are chief criteria for determining the appropriate type determining the system selection. Primarily, the touch system integrator must determine with what implement the user will touch the sensor with & what price the application will support.

Applications requiring activation by a

gloved finger or arbitrary stylus such as a plastic pen will specify either a low cost resistive based sensor or a higher cost infra-red (IR) or surface acoustic wave (SAW) system. Applications anticipating bare finger input or amenable to a tethered pen comprises of the durable & fast capacitive touch systems. A higher price tag generally leads to increased durability better optical performance & larger price.

The most commonly used systems are

generally the capacitive & resistive systems. The other technologies used in this field are Infrared technology & SAW (surface acoustic wave technology) these technologies are latest in this field but are very much expensive.

1. Introduction

To avoid shoot-though in voltage source inverters (VSI), dead-time, a small interval during which both the upper and lower switches in a phase-leg are off, is introduced into the standard pulse width modulation (PWM) control of VSIs. How­ever, such a blanking time can cause problems such as output waveform distortion and fundamental voltage loss in VSIs, es­pecially when the output voltage is low.

To overcome dead-time effects, most solutions focus on dead-time compensation  by introducing complicated PWM compensators and expensive current detection hardware. In practice, the dead-time varies with the gate drive path propa­gation delay, device characteristics and output current, as well as temperature, which makes the compensation less effective, especially at low output current, low frequency, and zero current crossing. Several switching strategies for PWM power converters have been proposed to minimize the dead-time effect. A dead-time minimization algorithm was also discussed earlier to improve the inverter output performance. A phase-leg configu­ration topology proposed prevented shoot through. However, an additional diode in series in the phase-leg increases complexity and causes more loss in the inverter. Also, this phase-leg configuration is not suitable for high-power inverters because the upper device gate turn-off voltage is reversely clamped by a diode turn on voltage. Such a low voltage, usually less than 2 V, is not enough to ensure that a device is in its off-state during the activation of its complement device.

High-power inverters usually need longer dead-time than those low-power counterparts. Also due to complicated struc­tures and severe parasitic parameter variations, in practice, the dead-time for high-power inverters requires specific adjustment and/or compensation, and usually this process is time-con­suming. For general applications, automatically eliminating dead-time by gate drive technology is a desired and complete solution. Gate drives with intelligent functions are in high demand due to the emerging technology of power electronics building blocks (PEBB) and intelligent power modules (IPM) because smart functions can improve power devices’ modu­larity, flexibility and reliability.

In this work, an effective dead-time elimination method is proposed. This method is based on decomposing of a generic phase-leg into two basic switching cells, which are configured with a controllable switch in series with an uncontrollable diode. Therefore, dead-time is not needed. In this paper, the effect of dead-time in VSIs will be first introduced. The prin­ciple of the proposed method to eliminate dead-time effect is explained in detail. Simulation and experimental results are provided to demonstrate the validity and features of the proposed novel method. Flexible implementation methods are also discussed.

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ABSTRACT

Cocoa is one of Apple Inc.’s native object-oriented application program environments for the Mac OS X operating system. It is one of five major APIs available for Mac OS X; the others are Carbon, POSIX (for the BSD environment), X11 and Java.

Cocoa applications are typically developed using the development tools provided by Apple, specifically Xcode (formerly Project Builder) and Interface Builder, using the Objective-C language. However, the Cocoa-programming environment can be accessed using other tools, such as Object Pascal, Python, Perl and Ruby, with the aid of bridging mechanisms such as PasCocoa, PyObjC, CamelBones and RubyCocoa, respectively. Also, under development by Apple, is an implementation of the Ruby language, called MacRuby, which does away with the requirement for a bridging mechanism. It is also possible to write Objective-C Cocoa programs in a simple text editor and build it manually with GCC or GNUstep’s makefile scripts. For end-users, Cocoa applications are considered to be those written using the Cocoa-programming environment. Such applications usually have a distinctive feel, since the Cocoa-programming environment automates many aspects of an application to comply with Apple’s human interface guidelines.

Main frameworks

Cocoa consists primarily of two Objective-C object libraries called frameworks. Frameworks are functionally similar to shared libraries, a compiled object that can be dynamically loaded into a program’s address space at runtime, but frameworks add associated resources, header files, and documentation.

Foundation Kit, or more commonly simply Foundation, first appeared in OpenStep. On Mac OS X, it is based on Core Foundation. Foundation is a generic object-oriented library providing string and value manipulation, containers and iteration, distributed computing, run loops, and other functions that are not directly tied to the graphical user interface. The “NS” prefix, used for all classes and constants in the framework, comes from Cocoa’s NeXTSTEP heritage.

Application Kit or AppKit is directly descended from the original NeXTSTEP Application Kit. It contains code with which programs can create and interact with graphical user interfaces. AppKit is built on top of Foundation, and uses the same “NS” prefix. A key part of the Cocoa architecture is its comprehensive views model. This is organized along conventional lines for an application framework, but is based on the PDF drawing model provided by Quartz. This allows creation of custom drawing content using PostScript-like drawing commands, which also allows automatic printer support and so forth. Since the Cocoa framework manages all the clipping, scrolling, scaling and other chores of drawing graphics, the programmer is freed from implementing basic infrastructure and can concentrate only on the unique aspects of an application’s content.

Technology Overview

Cocoa helps you create commercial-grade applications quickly and efficiently. It is an advanced, mature object- oriented development environment that enables you to create complex software with surprisingly few lines of code. Through a seamless integration of tools and Cocoa API, the design and construction of a user interface is largely a matter of dragging windows, buttons, and other objects from palettes, initializing their attributes, and connecting them to other objects. Cocoa also defines a model for applications and implements most aspects of application behavior; you simply fit into this model the code that makes your application unique.

The programmatic interfaces of the core Cocoa frameworks, Foundation and Application Kit, simplify access to most of the technologies on which Mac OS X is based, such as Quartz, Bonjour networking, Core Text, and the printing system. Although these interfaces are in Objective-C, you can integrate code written in other languages into your Cocoa projects, including C++ code and C code. Because Objective-C is a superset of ANSI C, frameworks with C APIs are compatible with Objective-C.

Implementations

The Cocoa frameworks are written in Objective-C, and hence Objective-C is the preferred language for development of Cocoa applications. Java bindings for the Cocoa frameworks (known as the “Java bridge”) are also available but have not proven popular amongst Cocoa developers. Further, the need for runtime binding means many of Cocoa’s key features are not available with Java. In 2005, Apple announced that the Java bridge was to be deprecated, meaning that features added to Cocoa in Mac OS X versions later than 10.4 would not be added to the Cocoa-Java programming interface. AppleScript Studio, part of Apple’s Xcode Tools makes it possible to write (less complex) Cocoa applications using AppleScript. Third party bindings available for other languages include PyObjC (Python), RubyCocoa (Ruby), CamelBones (Perl), Cocoa#, Monobjc (C#) and NObjective(C#).There are also open source implementations of major parts of the Cocoa framework that allows cross- platform (including Microsoft Windows) Cocoa application development, such as GNUstep, and Cocotron

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Download Full Article Cocoa.doc

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