Touchscreens or Human Machine Interface (HMI)

A touchscreen is an electronic visual display that the user can control through simple or multi-touch gestures by touching the screen with one or more fingers. Some touchscreens can also detect objects such as a stylus or ordinary or specially coated gloves. The user can use the touchscreen to react to what is displayed and to control how it is displayed (for example by zooming the text size).

The touchscreen enables the user to interact directly with what is displayed, rather than using a mouse, touchpad, or any other intermediate device (other than a stylus, which is optional for most modern touchscreens).

Touchscreens are common in devices such as game consoles, all-in-one computers, tablet computers, and smartphones. They can also be attached to computers or, as terminals, to networks. They also play a prominent role in the design of digital appliances such as personal digital assistants (PDAs),satellite navigation devices, mobile phones, and video games and some books.

The popularity of smartphones, tablets, and many types of information appliances is driving the demand and acceptance of common touchscreens for portable and functional electronics. Touchscreens are found in the medical field and in heavy industry, as well as for automated teller machines (ATMs), and kiosks such as museum displays or room automation, where keyboard and mouse systems do not allow a suitably intuitive, rapid, or accurate interaction by the user with the display's content.

There are different types of touch screen

Resistive-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.   

                                     

Capacitive – he 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 is 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.

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.

Infra red – works with small infra red LED’s mounted around the outer edges of the glass front and basically divides the surface of the screen into small squares, making it extremely accurate. You can also use a stylus or have gloves on to make this work as it does not require a conductor, your finger, to make it work. 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.

Surface Acoustic Wave (SAW) – are the most sensitive of the touch screens as it works by sending an ultrasonic wave across the screen, when the screen is touched the ultrasonic beam is altered and the information is sent to the touch controllerThe 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.

The Plural Touch Technology..!!

The plural touch technology or the Multi touch is a variant of the touchscreen technology which can detect two or more touches over its display area at the same time. Some of the common functionalities that require multitouch interface are zooming in, zooming out, rotating objects, panning through a document, virtual keyboard, etc. Multi touch Applications  technology are found in smart phones like iPhone, Samsung Galaxy, Nokia N8, Nexus S, Microsoft Touchtable, Apple’s iPad and many more.