Touchscreen technology is the direct
manipulation type gesture based technology. Direct manipulation is the ability
to manipulate digital world inside a screen without the use of
command-line-commands. A device which works on touchscreen technology is coined
as Touchscreen. A touchscreen is an electronic visual display capable of
‘detecting’ and effectively ‘locating’ a touch over its display area. It is sensitive
to the touch of a human finger, hand, pointed finger nail and passive objects
like stylus. Users can simply move things on the screen, scroll them, make them
bigger and many more.
Hailing the History..!!
The first ever touchscreen was developed by
E.A Johnson at the Royal Radar Establishment, Malvern, UK in the late 1960s.
Evidently, the first touchscreen was a capacitive type; the one widely used in
smart phones nowadays. In 1971, a milestone to touchscreen technology was
developed by Doctor Sam Hurst, an instructor at the University of Kentucky
Research Foundation. It was a touch sensor named ‘Allograph’. Later
in 1974, Hurst in association with his company Demographics came up with the
first real touchscreen featuring a transparent surface. In 1977, Demographics
developed and patented a resistive touchscreen technology, one of the most
popular touchscreen technologies in use today.
Ever since then, touchscreen displays are
widely used in computers, user interactive machines, public kiosks, point of
sale applications, gaming consoles, PDAs, smart phones , tablets, etc.
Types of Touchscreen Technology
Let us now give an engineer’s eye to this
revolutionary technology. A touchscreen is a 2 dimensional sensing device made
of 2 sheets of material separated by spacers. There are four main touchscreen
technologies:
1) Resistive
2) Capacitive
3) Surface Acoustic Wave
4) Infrared
1. Resistive Touchscreen
Technology
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.
Some of the popular devices that use Resistive
Touchscreen are Nintendo DS, Nokia N97, HTC Touch Pro2, HTC Tattoo, Sony
Ericsson Satie, etc.
These systems transmit only 75% of light from
the monitor. The resistive touchscreen is further divided into 4-, 5-, 6-, 7-
and 8-wired resistive touchscreen. While the constructive design of all these
modules is similar there is a major distinction in each of its method to
determine the coordinates of touch.
The Four-wire
Resistive Touchscreen uses both the layers to calculate the axes
information of the touch. Touch measurement in the 4-wire is a 2 step process.
The x-coordinate of the touch point is calculated by creating a voltage
gradient on the flexible layer, and the y-coordinate is determined by creating
a voltage gradient along the bottom layer.
Pros and Cons: Consequently, the 4-wire resistive touchscreen is less durable,
feebly accurate and can drift with environmental changes. However these
negatives are divulged only with large-sized touchscreen. These are relatively
cheap, easily available and consume low power.
The Eight-wire Resistive Touchscreen is simply a variation of the 4-wire one with the addition of 4
sense wires, two for each layer. The sensing points aid in reducing the
environmental drift to increase the stability of the system. The 8-wire systems
are employed in sizes of 10.4” or larger where the drift can be significant.
The Five-wire Resistive Touchscreen do not uses the coversheet (flexible layer) in determining the
touch coordinate. All the position sensing is employed on the stable glass
layer. In this design, one wire goes to the coversheet and four wires are
deployed to the four corners of the bottom sheet. The coversheet only acts as a
voltage measuring probe. The functioning of the touchscreen remains unscathed
even with changes in the uniformity of the conductive coating over the
coversheet.
Pros and Cons: Highly durable, accurate and
reliable. This technology involves complex electronics and is expensive.
However, it can be used in sizes up to 22”.
The Six and Seven wire resistive touchscreen is also a variant to the 5 and 4 wire technology respectively. In the
6-wire
resistive touchscreen an extra ground layer is added behind the glass plate
which is said to improve system’s performance. While, the seven–wire variant
has two sense lines on the bottom plate. However, these technologies are as
prevalent as their counterparts.
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