Touch Screen Technology – Working

Nowadays, there are a lot of touch screen monitors available in the market. They are made available in displays for computers, personal digital assistants, mobile phones and video games.

A touch screen contains a visual display area which can be sensitive to the touch of our finger or other passive components. A touch screen is only called so if the contact made with it is physical in nature. The common physical contacts made for a touch screen technology is the use of fingers or a pen. If the contact is made with an active component such as a light pen, they cannot be called a touch screen.

The use of a touch screen brings in a lot of advantages. They help us to interact without the help of an additional component such as a mouse or a touch pad. Even if there is an additional component, like a stylus, which is used instead of our fingers, they can be attached to our mobile phones and can be easily carried around.

This technology is now being used in heavy industries and also places where the user feels unsatisfied in using a mouse or keypad. They are also used in museum displays where the technology helps them to make a quick and accurate interaction with the content. We can also see their applications in ATM’s.

TAKE A LOOK : WORKING OF ATM

Emergence of Touch Screen Technology

The first touch screen enabled brand was the HP-150 computer released in the year 1983. Though it did not have the same features as the new ones, it had a 9-inch CRT screen which was surrounded by transmitters and receivers. These transmitters and receivers were used to detect the precise position of the non-transparent objects on the screen. Though the technology was invented during the end of 1960’s they were only used in computer assisted learning terminals during the year 1972.

During that time, the technology was only developed to sense the availability of one point of contact at a time. This technology has further been moved to ones having multi-touch screen pads. In the beginning, the touch screen technology was not made in chips or mother-boards. They were made as separate components by after-market system integrators.

Touch Screen – Construction and Working

In the construction of a touch screen there are some parameters that have to be fulfilled. They are

• The recognition of the touch on the display [including multi-touch].
• Mechanism to find out the location of the display and to carry on the appropriate command.

The most commonly used technologies are the resistive and capacitive sensing technologies [Both are explained below in detail]. For both these methods a touch screen should have four layers.

• A conducting metal coating with a poly-ester coating on the top. The metal coating should be transparent in nature.
• A spacing layer which is mostly an air-gap.
• A glass layer beneath the spacing with a conducting transparent coating on its top.
• An adhesive layer beneath the glass layer. This layer is mostly used for mounting purposes.

When a person presses his finger on the top of the screen, there will be a change in the electrical current in the display module. This change is measured in either ways explained below and the exact location of touch and the amount of force applied is calculated. Later, the command to be carried out is passed on to the operating system and the command is carried out.

Types of Touch Screen Technology

1. Resistive Touch Screen Technology

This type of a touch screen uses two layers that are coated with a resistive and a conductive material. These two layers are separated from each other with the help of an air gap or spacers.   On top of the whole mechanism will be a layer to provide resistance to scratches. The monitor of the display is made operational in nature. Thus, when our finger touches the screen, a contact is made between the two layers and current flows through them. As the layers make contact at the same point, the correct location of the point is noted. The location is calculated by the computer in course of the change in the electric field occurred by our touch. Thus when the position is known, it is passed on to a driver in the device which codes it and sends it to the OS of the device.

This technology can be used with the contact of any object like finger, pen, and stylus and so on. Thus it is also considered as a passive technology.

Advantages

• They are very accurate and can be used for high resolutions up to 4096X4096 dpi.
• Very cost effective in comparison with other technologies.
• It can also be used in multiple touch screen pads.
• It can transmit almost 75% of the light from the monitor.

Disadvantages

As the device is also used as a passive technology there will be problems regarding hand written notes taken on a stylus. As the person cannot use a whole hand down on the screen while he is writing there has to be a trade-off between the property of using a finger as a stylus and the pressing of a whole hand on the screen.

Capacitive Sensing Technology

This is one of the most widely used techniques for touch screens. This technology is based on the capacitor coupling effects. It has been used in devices like MP3 players, computer monitors, mobile phone displays and so on. As this technology has advantages like detecting the correct position at a very small time, less cost in production, and also a very unique human—device interface, it is widely used. It also has properties like multiple touch sensing and also gesture based touch screens. The latest and most famous gadget to be released with this technology is the Apple i-Pod click wheel. This mechanism is more advantageous than the resistive sensing because it can transmit to a maximum of 90% of the light from the monitor. Thus a much better vision can be obtained from these screens.

Here also, a glass panel is arranged on top of which a layer that is able to store electrical charge is kept. When the monitor is touched by the user, the charge begins to move from the layer to our body. This decrease in the charge on the conductive layer is measured with the help of electronic circuits which are placed inside the monitor. As the electronic circuits are placed on each corner of the monitor the difference in charge attained at each corner is calculated by the computer and the exact position of the touch is obtained. This information is then passed on to the touch-screen driver software.

Surface Acoustic Wave Technology

In this technology the use of ultrasonic waves are adapted. A glass plate is taken and two transducers are placed on the x and y axes of it. One transducer is used for sending the signal and the other is used for the reception. The glass plates will also have reflectors setup on them. These reflectors are used to reflect the electrical signal from one transducer to another. Thus when we touch the touch screen, there will be a difference in the wave and this difference will be understood by the receiving transducer. Thus, the exact position of the touch is calculated. This is the most efficient technology when compared to capacitive and resistive sensing as 100% of the light is transmitted from the monitor. Thus the screen clarity will be the highest.

This advantage makes way for this technique to be used in high end graphics devices. The disadvantages are that even a slight scratch on the surface can cause the damage of the screens. Dust and other contaminations can cause the change of its functions.

Strain Gauge

Strain gauge has already been explained in an earlier article. To know more about strain gauge click on the link below.

TAKE A LOOK : WORKING OF STRAIN GAUGE

With this technology, strain gauges are mounted on the four corners of the screen. As soon as the screen is touched, a deflection occurs which is picked up by the strain gauge. This device can also be used for the measurement of the Z-axis and also the amount of force exerted while touching the screen.  The main application of such screens is in devices like ticket machines.

Optical Imaging Technique

This is the most modern technique used in touch screens. It consists of a number of image sensors that are kept on the four corners of the screen. A field of infrared lights are set inside the monitor. When a person touches the screen, a shadow will build up which will be received by the sensors. This is more than enough for the sensors to calculate the exact location of the touch and also the size of the object that touched the screen.