We have already known about “Touchscreen” in our previous post.Let’s we know their technologies.There are a variety of touchscreen technologies that have different methods of sensing touch.
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. An electrical current runs through the two layers ,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.
Resistive touch is used in restaurants, factories and hospitals due to its high resistance to liquids and contaminants. A major benefit of resistive touch technology is its low cost. Disadvantages include the need to press down, and a risk of damage by sharp objects.Resistive touch screen panels are not affected by outside elements such as dust or water.
Some of the popular devices that use Resistive Touchscreen are Nintendo DS, Nokia N97, HTC Touch Pro2, HTC Tattoo, Sony Ericsson Satio, 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 aligns of touch. Let’s discuss about these:-
— 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.
— 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 impulse to increase the stability of the system. The 8-wire systems are applied in sizes of 10.4” or larger where the impulse can be.
— The Five-wire Resistive Touchscreen do not uses the flexible layer in determining the touch align. All the position sensing is used on the stable glass layer. In this design, one wire goes to the coversheet(flexible layer) and four wires are distributed to the four corners of the bottom sheet. The coversheet only acts as a voltage measuring investigation.
— 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.
2. Capacitive Touchscreen Technology :
A capacitive touchscreen panel consists of an insulator such as glass, coated with a transparent conductor such as indium tin oxide . As the human body is also an electrical conductor, touching the surface of the screen results in a distortion of the screen’s electrostatic field, measurable as a change in ent to the controller for processing.
The Capacitive Touchscreen Technology is the most popular and durable touchscreen technology used all over the world at most.Some of the devices using capacitive touchscreen are Motorola Xoom, Samsung Galaxy Tab, Samsung Galaxy SII, Apple’s iPad.
Capacitive Toouchscreen is also divided into two capacitive touchscreen.They are:
— Surface Capacitance–
In this technique only one side of the insulator is coated with a conducting layer. While the monitor is operational, a uniform electrostatic field is formed over the conductive layer. Whenever, a human finger touches the screen, conduction of electric charges occurs over the uncoated layer which results in the formation of a dynamic capacitor. The computer or the controller then detects the position of touch by measuring the change in capacitance at the four corners of the screen. It is therefore most often used in simple applications such as industrial controls and kiosks.
In the Projected-Capacitive Touchscreen Technology, the conductive ITO layer is inscribed to form a grid of multiple horizontal and vertical electrodes. It involves sensing along both the X and Y axis using clearly etched ITO pattern. The projective screen contains a sensor at every intersection of the row and column, thereby increasing the accuracy of the system.
There are two types of projected capacitive touchscreen: Mutual Capacitance and Self Capacitance.
1) Mutual capacitance–
In mutual capacitive sensors, there is a capacitor at every intersection of each row and each column. A 16-by-14 array, for example, would have 224 independent capacitors. A voltage is applied to the rows or columns. Bringing a finger or conductive stylus close to the surface of the sensor changes the local electrostatic field which reduces the mutual capacitance.
Self-capacitance sensors can have the same X-Y grid as mutual capacitance sensors, but the columns and rows operate independently. With self-capacitance, the capacitive load of a finger is measured on each column or row electrode by a current meter.
3. Surface acoustic wave Touchscreen Technology:
Surface wave technology uses ultrasonic waves that pass over the touch screen panel. When the panel is touched, a portion of the wave is absorbed. This change in the ultrasonic waves registers the position of the touch event and sends this information to the controller for processing. On the monitor of a surface acoustic wave system, two transducers (one receiving and one sending) are placed along the x and y axes of the monitor’s glass plate. Also placed on the glass are reflectors , they reflect an electrical signal sent from one transducer to the other. The receiving transducer is able to tell if the wave has been disturbed by a touch event at any instant, and can locate it accordingly. The wave setup has no metallic layers on the screen, allowing for 100-percent light throughput and perfect image clarity. This makes the surface acoustic wave system best for displaying detailed graphics (both other systems have significant degradation in clarity). The surface acoustic wave setup is usually the most expensive.
4. Infrared Touchscreen Technology :
An infrared touchscreen uses an array of X-Y infrared LED and photodetector pairs around the edges of the screen to detect a disruption in the pattern of LED beams. These LED beams cross each other in vertical and horizontal patterns. This helps the sensors pick up the exact location of the touch.
A major benefit of such a system is that it can detect essentially any input including a finger, gloved finger, stylus or pen. It is generally used in outdoor applications and point of sale systems which can not rely on a conductor (such as a bare finger) to activate the touchscreen.
Unlike capacitive touchscreens, infrared touchscreens do not require any patterning on the glass which increases durability and optical clarity of the overall system. Infrared touchscreens are sensitive to dirt/dust that can interfere with the IR beams, and suffer from parallax in curved surfaces and accidental press when the user hovers his/her finger over the screen while searching for the item to be selected.