RESISTIVE AND CAPACITIVE

TOUCH SCREEN

By

Abdul Muqeed

11011A0449

Overview

• Introduction

• Working

• Types of technologies

• Resistive touch

• Capacitive touch

• Advantages and advancements

• Conclusion

Introduction

• A touch screen is an electronic visual display that the user cancontrol through simple or multi-touch gestures by touching thescreen with a special stylus/pen and-or one or more fingers.

• The user can use the touch screen to react to what is displayedand to control how it is displayed (for example by zooming thetext size).

• The touch screen enables the user to interact directly with whatis displayed, rather than using a mouse, touchpad, or any otherintermediate device.

Working

• A touch screen has three main components:

Touch sensor

Touch Controller

Software driver

• The touch screen itself is an input device, so it needs to becombined with a monitor and a PC to make a complete touchinput system.

Touch Sensor• Each touchscreen uses a different

method to sense touch input. Oftenthese are a plastic or glass panel placedunder the bezel of the LCD screen.

• A touch screen sensor is a clear glasspanel with a touch responsive surface.It is placed over a display screen sothat the responsive area of the panelcovers the viewable area of the videoscreen.

• The sensor generally has an electricalcurrent or signal going through it andtouching the screen can cause a signalchange. This change is used todetermine the location of the touch.

Touch Controller• The controller connects between the touch sensor and the PC.

It takes information from the touch sensor and translates it intoinformation that PC can understand.

• The controller determines what type of interface/connectionwill be needed on the PC. Controllers are available that canconnect to a Serial/COM port (PC) or to a USB port.

• MCF227x,PIC 18F452.

Software driver• The driver allows the touch screen and computer to work

together. It tells the computer's operating system how tointerpret the touch event information that is sent from thecontroller.

Types of technologiesThere are a variety of touch screen technologies that have

different methods of sensing touch

• Resistive touchscreen

• Capacitive touchscreen

• Infrared touchscreen

• Surface acoustic wave (SAW) touchscreen

• The resistive touchscreen consists of a flexible top layer made ofPolyethylene (PET) and a rigid bottom layer made of glass.

• Both the layers are coated with a conducting compound called IndiumTin Oxide (ITO) and then spaced with spacers.

• While the monitor is operational, an electric current flows between thetwo layers. When a touch is made, the flexible screen presses down andtouches the bottom layer.

• A change in electrical current is hence detected and the coordinates ofthe point of touch is calculated by the controller and parsed intoreadable signals for the operating system to react accordingly.

Resistive Touchscreen Technology

• When the touch screen ispressed, contact is madebetween the grid on theglass and the grid on thefilm.

• The voltage of the circuit ismeasured, and the X and Ycoordinates of the touchposition is calculated basedon the amount ofresistance at the point ofcontact.

• This analog voltage isprocessed by ADC to createa digital signal that thedevice's controller can useas an input signal from theuser.

• One of the big advantages of resistive touch panels is thatthey are relatively inexpensive to make. Another is that youcan use almost anything to create an input signal: finger tip,fingernail, stylus -- just about anything with a smooth tip.

Resistive touchscreens are of 4 modes

• 4-wire

• 8-wire

• 5 and 7 wire

4-wire• A 4-wire touch screen is made from two layers, each with a resistive

coating. The bottom layer is rigid, but the top one is flexible. Both layersare provided with voltage

• The basic idea is to create a voltage divider. Detecting the voltage at thedivision point (the touch point) allows for calculating the relativeposition of the touch point with respect to the two rails.

• To get the coordinates for a single point, First a voltage is applied acrossthe x-axis plane, and the contacts for the y-axis plane are allowed tofloat.

• The resistive coating on the touch screen creates a voltage gradientacross the plane. If the top layer is pressed, it flexes and makes contactwith the bottom layer.

• The y-axis plane now has a voltage equal to the voltage on the x-axisplane at the point of contact. The voltage on the y-axis plane can bemeasured and used to obtain the x-coordinate.

• The process is repeated again to get the y-coordinate.

8-wire• An 8-wire touch screen is based on the same basic technology as

a 4-wire touch screen. Again, four wires are used to providepower at the edges of the touch screen.

• The extra four wires are used to sense the actual voltage appliedat the edges of the touch screen. These sense wires are added tocompensate for offset errors.

• An 8-wire system is more commonly used for larger touchscreens (about twenty centimeters, or eight inches, and up).

• The accuracy of touch point placement degrades as the screenbecomes larger, because the resolution is spread across a biggerdistance.

• Therefore, loss of accuracy due to offset error is a biggerconcern. Hence 8-wire is used for greater accuracy.

5-wire and 7-wire• 5-wire touch screens make some improvements on the older 4-wire

technology. The construction of the panels are similar, but for a 5-wiretouch screen all four bus bars are connected to the lower, non-flexiblelayer of the screen.

• The voltage gradients are always applied to the rigid bottom layer.Because the voltage gradient layer does not come into direct contactwith the user and does not bend. Hence better durability.

• 7-wire touch screens add two additional sense lines to the 5-wireinterface.

• One sense line is used to detect offset on one of the x-axis bus bars,and the second is used to detect offset on one of the y-axis bus bars.Again, this helps to increase the accuracy of touch measurements andreduce the need for calibration.

• A capacitive touchscreen panel consists of an insulator suchas glass, coated with a transparent conductor such as indium tinoxide(ITO).

• As the human body is also an electrical conductor, touching thesurface of the screen results in a distortion of thescreen's electrostatic field, measured as a change in capacitance.

• Capacitive touch gets its name from the electrical distortion thatresults in the screen's capacitive field when impressed upon bybody capacitance, or conductor of electric charges.

• This enables capacitive touchscreens to not require any actualforce to be applied to the screen’s surface; at the same time,capacitive screens typically don't respond to styluses or glovedhands due to the lack of electrical impulses generated.

Capacitive Touchscreen Technology

• Capacitive touchscreen is afour multi-layer glass. Thetwo sides of the glasssubstrate are coated withuniform conductive ITO(indium tin oxide) coating.

• The thickness of 0.0015millimeter silicon dioxide hardcoating are coated on thefront side of ITO coating layer.There are electrodes on thefour corners for launchingelectric current.

• Small amount of voltage is appliedto the electrodes on the fourcorners . A human body is anelectric conductor, so when thescreen is touched with a finger, aslight amount of current is drawn,creating a voltage drop.

• The current respectively drifts tothe electrodes on the four corners.Theoretically, the amount of currentthat drifts through the fourelectrodes should be proportionalto the distance from the touch pointto the four corners.

• The controller precisely calculatesthe proportion of the currentpassed through the four electrodesand figures out the X/Y coordinateof a touch point.

Advantages

• Touchscreens improves the human-computer interface and helps improving the user’s experience.

• Touchscreens provide an easy to understand, intuitive interface for the human brain.

• Fumbling with a mouse and keyboard isn’t always the easiest thing to do and touchscreen technology can help as they have easier hand eye coordination than mice or keyboards

• Touch screens are the fastest pointing devices. No extra workspace is required as with other pointing devices.

Multi-touch screens• multi-touch refers to the ability of a surface to

recognize the presence of more than one or morethan two points of contact with the surface.

• Capacitive display continue to develop thinner andmore accurate touchscreens, with touchscreensfor mobile devices now being produced with 'in-cell' technology that eliminates a layer, such asSamsung's Super AMOLED screens, by building thecapacitors inside the display itself.

Advancements

•This type of touchscreen reduces the visible distance (withinmillimetres) between the user's finger and what the user is touching on thescreen, creating a more direct contact with the content displayed andenabling taps and gestures to be more responsive.

Conclusion• As it is very friendly, fast, accurate, easy for the

novices and fun to operate. It has been widelyaccepted.

• Today, This Technology is been adopted by computer,mobile users of all abilities because it is innovative,simple.

• Designers are trying to use touchscreen to simplifyinput commands for largely unsophisticated computerusers.

• In future there may be no usage of mouse and keyboards as they will be replaced by touchscreens.

THANK YOU