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Screening Touch Screens

Nowadays we are surrounded by numerous gadgets- Cellphones, Tablets, Handhelds, Smart Kiosks, Gaming Consoles. The list is virtually endless and more devices keep being added every week. But there is one common input for all these devices: the Touch Screen.

Touch Screens come in all shapes and sizes. They are easy to use and they have found their application in almost all of our devices. We all know how to use these screens, but what we don’t know is how these screens manage to act as both input and output devices at the same time.

The Touch Screens that we find in our communication devices are divided into three types:

1. Resistive Touch Screens: This type of screen is made up of three layers; i.e. a Conductive layer, a Resistive layer and a Protective Sheet to protect the other two layers.

The conductive and the resistive layers are placed together facing each other with a tiny gap in-between. One layer has conductive connections along its side axis whereas the other along top and bottom axis. A voltage is applied to one layer which is sensed by the other layer. When an object, like a finger or a stylus presses down on the outer surface, the two layers touch to become connected at that point: The position is the calculated by the coordinates of the pressing point on the screen.

This type of screens is rugged, durable and is cost effective for low priced devices. But, as it comprises of three layers, it lets only 75% of light pass through, so is not a good choice for devices with a sharp image.
Image Link: http://www.planartouch.com/101/images/resistive-how-final.jpg

2. Capacitive Touch Screen: This type of screen houses a thin electronically charged sheet placed against the glass. When a finger touches the screen, a little charge of the finger shifts to the screen. The position is calculated by the point at which there is a difference in the charge which is used to click or process any application.
This screen has only two layers and hence allows over 90% of light to pass through which results in a sharp display image. Unlike resistive touch screens, they respond only to finger touch and not to other objects like stylus.
Image Link: http://mobilephones.pk/reviews/wp-content/uploads/2011/07/ctdisp_r.gif

3. Surface Acoustic Wave Touch Screen: This is more advanced of all the touch screens. In this screen three sheets are used to perform the action: A Sending transducer, a Receiving transducer and a Reflector layer. Both, sending and receiving, transducers enable the screen to sense the outer touch and reflectors help in giving the proper response.

When the screen is touched, a wave produced which is transferred from sender transducer to the receiver, where reflectors get the message. This wave travels back to the specific place and perform the application action. These screens are fast and allow 100% light emitting resulting in a sharp & clear image. But these screens are too expensive and have a very short life, so they find their applications in very specialized processes.
Image Link: http://www.etouchtechnologies.com/product_saw_workspic.gif


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