How do touch screens work – process explained

How do touch screens work – process explained

Touch screens are a common feature of mobile phones these days. The screen is made to accept the commands like scroll up, scroll down and click, etc. To offer a seamless experience to the users. But, how exactly this touch screen technology works, let’s find.

The touch screens are broad of two types– resistive touch screens and capacitive touch screens. The screens are multi-touch as all the units of space of the screen are touch-sensitive and deliver a certain response like swiping left and right the screen or moving it up and down.

It is said that capacitive touch screens offer the better quality multi-touch experience to the users. These screens work on the conductive touch of the human finger or material like a stylus or pen. The capacitive touch delivers more utility because it can be operated both by the finger as well as the pen. In this screen, the panel stores electrical charge. When the touch happens, a signal develops which is actually the result of a change in capacitance of that particular spot.

Capacitive touch screens are used in tablets, mobile phones, iPhones and iPods, etc. In fact, most of the products with the screen in the present generation come with a capacitive screen feature in order to save the users from the hassle of carrying stylus around for inputting commands.

Employing of touch technologies in mobile phones and tablets offers better screen space. The keyboard becomes in-built and appears only when typing is required. Thus, the user gets to enjoy more screen space for watching videos or just going through any web page.

How do touch screens work – the real phenomenon behind it

Depending upon the way the screen recognizes the human touch, it can be categorized into three basic systems. These systems differ from each other in the way they create a capacitor and transmit signal. These basic systems are as below.

1) Resistive touch screen

A resistive screen comprises of two panels joined with each other through spacers. One of these panels is the resistive layer and the other is conductive. An additional anti-scratch layer is placed above these two panels to complete the composition. When the user puts on the gadget, the electrical current runs through the screen portion. On touching the screen, the contact is imprinted on both the layers at the same spot. This causes a change in the electrical field.

This change is then defined by coordinates, which are further communicated to the computer. The computing component or driver inside the gadget converts the coordinates to a language that the operating system can relate to and respond accordingly. All these changes happen in the time span much smaller than seconds and this is how a command using touch generates and the gadget’s operating system then processes it. You must know that the resistive touchscreens do not give as clear a picture as a capacitive screen delivers.

The resistive screen literally resists the touch. One can even notice a slight bend that appears on the screen when the user touches it with a finger. The touch is registered only when both the resistive and conductive layers are reading the contact. That is why; some people complain about these screens to be not so smooth to use.

Let’s discuss the reason for it while understanding the working of the capacitive screen.

2) Capacitive touch screen

In the capacitive system, the change in the electric field is created by passing of charge from the screen to the user’s finger. The screen has a layer with an electric charge stored in it. This charge transfers to the user when he or she touches the screen. Thus, the electrical field is changed. This change is sensed by the circuits present on the sides of the screen in a capacitive touch-screen. The change then meets the same fate as that in a resistive screen, that is, the computer calculates coordinates and the driver conveys the coordinate information to the operating system. Finally, the command with the help of touch is created which is actually the response of the operating system.

The clearer picture in the capacitive touch screen is attributed to the fact that this screen is able to transmit 90% of the light, unlike resistive screen which transmits only 75%.

3) Surface acoustic wave system

This system is of advanced type as compared to the above two. The glass plate screen has two transducers placed on the x and y-axis. Along with the transducers, there are signal reflectors also added. These reflectors allow the sound waves to travel between the transducers. The receiving transducer makes out the change when the user touches the screen. It also can detect the point of touch on the screen. The signals continue to flow between the transducers with the help of reflectors. The flow is disrupted with the touch which the receiving transducer detects and reports to the operating system through driver software.

If we compare the three systems, the finest is the surface acoustic wave system. It is responsible for the much-advanced clarity in the picture and for the brightness of the screen. This is because of its ability to reflect the light 100%. The surface acoustic wave system, therefore, is used for the touchscreen device that displays graphics and images mostly. The added clarity certainly enhances the visual experience.

In terms of flexibility, the surface acoustic wave system works almost the same as the resistive screen. The difference in the wave will generate no matter what is used to touch the screen. The capacitive touch screen requires only the input from electrically conductive sources like a human finger, whereas, the resistive and surface acoustic wave systems create change in the electric field when touched by a metallic tip, rubber tip or a human finger. The quality of the picture on the resistive screen is the poorest of all three. Surface acoustic wave screens deliver the brightest and crispiest pictures among the three.

Newer technologies are also on the way

As of now, the market is mostly comprising of capacitive touch screens. However, the newer ways of creating voltage drop are also under development. One such system is frustrated total internal reflection. Since nothing is absorbed or deviated, as the name suggests, the complete internal reflection causes brilliant illumination of the screen. When the FTIR screen is touched, the complete scattering of infrared light creates the thrust of light waves. The tiny cameras at the back of the screen capture this sudden burst of optical waves. This change in optics creates change in signal just the way it happens in the capacitive screen. The driver software detects the change in the optical field and translates it to a command by sending it to the operating system for interpretation.

So, this answers the query ‘how do touch screens work?’. The systems are making use of principles like conduction, insulation, voltage drop, change in the optical wave, etc. to make screens work. So, when your screen stops working, it is just that the electric current generation mechanism is out of order.

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