How Touchscreens work? Learn in Tamil!

Note: This blog is a textual transcript of our video, not an in-depth article.

Before a few years, we used to own phones like Nokia 1100, 3315 and then we bought camera phones like 6600 or MusicExpress. Even then, a lot of people were still using landlines. But these days, everyone owns an android phone or an iPhone. In all these phones, an important technological advancement is the touch screen which they added after removing the buttons. Touch screen is something that works based on human touch. First iPhone was the first phone that had a full screen touch digitizer. It has been 10 years since the first iPhone came, but lot of us still don’t know how a touch screen works.

Not just phones, but touchscreen is also used in ATM machine, credit card machine, and aeroplane TVs. There are 2 types of touch screens, one is resistive touch screen and another is capacitive touch screen. Common in both is the technology where change in electric signal gets translated into location of touch. In resistive, it’s based on pressure of touch and in capacitive touch screen, it’s based on conductivity of our finger.

First let’s look at resistive touch screens, which came many years back. There are 2 layers, first layer which is flexible and transparent, made with materials like polyethylene. Bottom layer is a strong layer made with material like glass. Top layer is called resistive layer and bottom layer is called conductive layer. The bottom layer is given a metal coating to make it conductive, with metal like indium tin oxide. Both these layers are separated by dots called spacers. When there is no touch, current flows normally over the conductive layer. When we touch the resistive layer, due to pressure, resistive layer will come in touch with conductive layer, and there will be a voltage change. The processor then finds the voltage change and maps it to location of touch (x,y) coordinates. This is resistive touch screen, strong and less expensive, but there are some disadvantages like no multi-touch, heavy reflection and needs more touch effort to make things work seamlessly.

Another type of touch screen is called capacitive touch screens. These are the ones that are there in our mobile phones. In these touch screens, there are many layers. The top layer is called protective layer, for e.g. our gorilla glass. Below this are two layers, driving lines layer and sensing lines layer. In both these layers there is a grid that has metal with thickness like our hair. These hair like grid are made of metals like indium tin oxide. There is an electrostatic field where these lines intersect and that is saved as neutral in our processor. When a conductive material touches the top layer, electrostatic field will change. Our finger is conductive, and when it touches the screen, electrostatic field will change and the processor will find the location. This works well for multi-touch, swiping and is also very accurate. It doesn’t work well with gloves.

There are several advancements in this technology in recent years. In cell and on cell technology. In these technology, the top layer is replaced with touch screen technology. ‘On cell’ is used by Samsung AMOLED display and ‘In cell’ is used from iPhone 5S onwards. Even though the manufacturing for these is difficult, it reduces the thickness of phone drastically.

Someone will be using a smart phone near you. Walk to them, ask them if they know about touch screens. If they say no, show this video to them and teach them how it works. Not just that, SUBSCRIBE to our channel, and keep talking science.

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