Touch Screen Displays

Touch Screen Displays

As all of us known about the touchscreen displays which we are using in our mobile phones, tablets, laptops and also it can be used in the smart TV displays. Instead of using keys we are using touchscreen displays. Using touchscreen we can interact directly with what is displayed.    

What is Touch Screen Technology?

Touchscreen technology is the direct manipulation type gesture based technology. Direct manipulation is the ability to manipulate digital world inside a screen without the use of command-line-commands. A device which works on touchscreen technology is coined as Touchscreen. A touchscreen is an electronic visual display capable of ‘detecting’ and effectively ‘locating’ a touch over its display area. It is sensitive to the touch of a human finger, hand, pointed finger nail and passive objects like stylus. Users can simply move things on the screen, scroll them, make them bigger and many more.

Hailing the History..!!

The first ever touchscreen was developed by E.A Johnson at the Royal Radar Establishment, Malvern, UK in the late 1960s. Evidently, the first touchscreen was a capacitive type; the one widely used in smart phones nowadays. In 1971, a milestone to touchscreen technology was developed by Doctor Sam Hurst, an instructor at the University of Kentucky Research   Foundation. It was a touch sensor named ‘Elograph’. Later in 1974, Hurst in association with his company Elographics came up with the first real touchscreen featuring a transparent surface. In 1977, Elographics developed and patented a resistive touchscreen technology, one of the most popular touchscreen technologies in use today.

Ever since then, touchscreen displays are widely used in computers, user interactive machines, public kiosks, point of sale applications, gaming consoles, smartphones, tablets, etc.

Types of Touchscreen Technology

Let us now give an engineer’s eye to this revolutionary technology. A touchscreen is a 2 dimensional sensing device made of 2 sheets of material separated by spacers. There are four main touchscreen technologies:

1)      Resistive

2)      Capacitive

3)      Surface Acoustic Wave

4)      Infrared

1.      Resistive Touchscreen Technology

The resistive touchscreen consists of a flexible top layer made of Polyethylene (PET) and a rigid bottom layer made of glass. Both the layers are coated with a conducting compound called Indium Tin Oxide (ITO) and then spaced with spacers. While the monitor is operational, an electric current flows between the two layers. When a touch is made, the flexible screen presses down and touches the bottom layer. A change in electrical current is hence detected and the coordinates of the point of touch is calculated by the controller and parsed into readable signals for the operating system to react accordingly. 

Some of the popular devices that use Resistive Touchscreen are Nintendo DS, Nokia N97, HTC Touch Pro2, HTC Tattoo, Sony Ericsson Satio, etc.

These systems transmit only 75% of light from the monitor. The resistive touchscreen is further divided into 4-, 5-, 6-, 7- and 8-wired resistive touchscreen. While the constructive design of all these modules is similar there is a major distinction in each of its method to determine the coordinates of touch.

The Four-wire Resistive Touchscreen uses both the layers to calculate the axes information of the touch. Touch measurement in the 4-wire is a 2 step process. The x-coordinate of the touch point is calculated by creating a voltage gradient on the flexible layer, and the y-coordinate is determined by creating a voltage gradient along the bottom layer.

Pros and Cons: Consequently, the 4-wire resistive touchscreen is less durable, feebly accurate and can drift with environmental changes. However these negatives are divulged only with large-sized touchscreen. These are relatively cheap, easily available and consume low power.

The Eight-wire Resistive Touchscreen is simply a variation of the 4-wire one with the addition of 4 sense wires, two for each layer. The sensing points aid in reducing the environmental drift to increase the stability of the system. The 8-wire systems are employed in sizes of 10.4” or larger where the drift can be significant.

The Five-wire Resistive Touchscreen do not uses the coversheet (flexible layer) in determining the touch coordinate. All the position sensing is employed on the stable glass layer. In this design, one wire goes to the coversheet and four wires are deployed to the four corners of the bottom sheet. The coversheet only acts as a voltage measuring probe. The functioning of the touchscreen remains unscathed even with changes in the uniformity of the conductive coating over the coversheet.

Pros and Cons: Highly durable, accurate and reliable. This technology involves complex electronics and is expensive. However, it can be used in sizes upto 22”.

The Six and Seven wire resistive touchscreen is also a variant to the 5 and 4 wire technology respectively. In the 6-wire resistive touchscreen an extra ground layer is added behind the glass plate which is said to improve system’s performance. While, the seven–wire variant has two sense lines on the bottom plate. However, these technologies are as prevalent as their counterparts. The Resistive Touchscreen works well with almost any stylus-like object.

2.      Capacitive Touchscreen Technology

The Capacitive Touchscreen Technology is the most popular and durable touchscreen technology used all over the world at most. It consists of a glass panel coated with a capacitive (conductive) material Indium Tin Oxide (ITO). The capacitive systems transmit almost 90% of light from the monitor. Some of the devices using capacitive touchscreen are Motorola Xoom, Samsung Galaxy Tab, Samsung Galaxy SII, Apple’s iPad. There are various capacitive technologies available as explained below.

Surface-Capacitive screens, in this technique only one side of the insulator are coated with a conducting layer. While the monitor is operational, a uniform electrostatic field is formed over the conductive layer. Whenever, a human finger touches the screen, conduction of electric charges occurs over the uncoated layer which results in the formation of a dynamic capacitor. The computer or the controller then detects the position of touch by measuring the change in capacitance at the four corners of the screen.

Pros and Cons: The surface capacitive touchscreen is moderately durable and needs calibration during manufacture. Since a conductive material is required to operate this screen, passive stylus cannot be used for surface capacitive touchscreen.

 In the Projected-Capacitive Touchscreen Technology, the conductive ITO layer is etched to form a grid of multiple horizontal and vertical electrodes. It involves sensing along both the X and Y axis using clearly etched ITO pattern.

The projective screen contains a sensor at every intersection of the row and column, thereby increasing the accuracy of the system. There are two types of projected capacitive touchscreen: Mutual Capacitance and Self Capacitance

3.      Surface Acoustic Wave Touchscreen technology

The Surface Acoustic Wave Touchscreen technology contains two transducers (transmitting and receiving) placed along the X-axis and Y-axis of the monitor’s glass plate along with some reflectors. The waves propagate across the glass and are reflected back to the sensors.  When the screen is touched, the waves are absorbed and a touch is detected at that point. These reflectors reflect all electrical signals sent from one transducer to another. This technology provides excellent throughput and image clarity.

  Pros and Cons: 100% clarity is obtained as no metallic layers are present on the screen, it can be operated using passive devices like stylus, glove or finger nail. Screen can get contaminated with much exposure to dirt, oil which may haunt its smooth functioning.

4.      Infrared Touchscreen Technology

In the Infrared Touchscreen Technology, an array of X- and Y- axes are fitted with pairs of IR Leds and photo detectors. The photo detectors detect any change in the pattern of light emitted by the Leds whenever the user touches the monitor/screen.

The potential novice touchscreen technology has many advantages over the conventional QWERTY keyboard and monitor. It is very flexible as opposed to its physical counterparts since the digital displays can be configured anytime at will of the user as per the functionalities. Touchscreen allows users to customize the interface for example alteration of language and size. By adjusting the size of the keyboard, user can utilize the spare area for display and other uses. With the decreasing size of computers and tablets these days, touchscreen is an added advantage. Multiple functions has to be performed on a small screen, touchscreen allows switching to a function at user’s will. For example, virtual keyboard which is an application of touchscreen is displayed on the screen only when the user allows it to be.

Apple iPhone: ‘Multitouch’ now is a trademark by Apple who rightly proved it with a bang with the first most successful multitouch device ever; the iPhone. The first iPhone was unveiled on January 9, 2007. iPhone is no less than a revolution in the touchscreen industry with its maestro functionalities and applications. It uses Mutual Capacitance Technology as its touchscreen. The capacitive touchscreen can only be operated by bare finger or multiple fingers for multi touch.   

Microsoft Surface: is a multi-touch product from Microsoft that allows multiple users to manipulate digital content through surface computing. The main feature of this product is its Surface’s interface: Direct interaction, multi-touch contact, object recognition and multi-user experience. It is not based on and limited by the conventional touch technology. The surface utilizes Frustrated Total Internal Reflection and underneath projectors for its display operation. It is indeed a milestone in the multi-touch scenario.

Reference:

Wikipedia.org

Electronics.Howstuffworks.com

Engineersgarrage.com

Books.google.com

Touchscreendisplays.ca

etouchtechnologies.com

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Vic