Input Devices- Touch Devices

Touch Screens

What is a Touch Screen?


A touch screen is an electronic visual display that can detect the presence and location of a touch within the display area.
The term generally refers to touching the display of the device with a finger or hand.
Touch screens can also sense other passive objects, such as a stylus.

How does a Touch Screen Work?


There are many layers of a touch screen that have many functions in order for a touch screen to work successfully. There are typically four layers;
  1. Top polyester layer coated with a transparent metallic conductive coating on the bottom
  2. Adhesive spacer
  3. Glass layer coated with a transparent metallic conductive coating on the top
  4. Adhesive layer on the backside of the glass for mounting.
When a user touches the surface, the system records the change in the electrical current that flows through the display.
Dispersive-signal technology, measures the piezoelectric effect the voltage generated when mechanical force is applied to a mexternal image Resistive-Touch-Screen.gifaterial that occurs chemically when a strengthened glass substrate is touched.
There are two infrared-based approaches. In one, an array of sensors detects a finger touching or almost touching the display, Thereby interrupting light beams projected over the screen. In the other, bottom-mounted infrared cameras record screen touches. In each case, the system determines the intended command based on the controls showing on the screen at the time and the location of the touch.

Advantages and Disadvantages



· Direct pointing to objects, direct relationship between hand and cursor movement because the hand is moving on the same surface that the cursor is moving, manipulating objects on the screen is similar to manipulating them in the manual world
· Fast
· Finger is usable, any pen is usable
· No keyboard necessary for applications that need menu selections only/ saves desk space
· Suited to novices, applications for information retrieval, high-use environments

  • Imprecise positioning, possible problems with eye parallax is the finger may be too large for accurate pointing with small objects/ a pen is more accurate.
  • Requires that users move the hand away from the keyboard; a stylus requires also hand movements to take up the pen.
  • Straining the arm muscles under heavy use Sitting/Standing position: The user has to sit/stand close to the screen.
  • The screen gets dirty from finger prints.
  • The user's hand, the finger or the pen may obscure parts of the screen.
  • Usually direct activation of the selected function, when the screen is touched; there is no special "activation" button as with a light pen or a mouse.

Common uses


  • IPods
  • Mobile Phones
  • Cash registers
  • Computer screens
  • Control devices

Cost Information


Prices of appliances with touch screens vary from £80 new and above, which is a reasonable price.

Touch Pads

What is a Touch Pad?

A touchpad is a pointing device consisting of specialized surface that can translate the motion and position of a user's fingers to a relative position on screen. They are a common feature of laptop computers and also used as a substitute for a computer mouse where desk space is scarce. Touchpad’s vary in size. They can also be found on personal digital assistants and some portable media players, such as the iPod using the click wheel. A touchpad is perhaps the most common kind of tactile sensor.

How does a Touch Pad Work?

Touch pads operate in one of several ways, including capacitive sensing and conductance sensing. The capacitative virtual ground effect of a finger, or the capacitance between sensors. Capacitance-based touch pads will not sense the tip of a pencil or other similar implement. Gloved fingers may also be problematic.
If the computer is powered by an external power supply, the detailed construction of the PSU will influence the virtual ground effect; a touchpad may work properly with one PSU but be jerky or malfunction with another. This has been known to cause touchpad problems when a manufacturer's PSU, which will have been designed to work with the touchpad, is replaced by a different type. This effect can be checked by touching a metallic part of the computer with the other hand and seeing if operation is restored. In some cases touching the power supply with some part of the body, or using the computer on the lap instead of on a desk, while working can restore correct operation.
While touch pads, like touch screens, by their design are able to sense absolute position, resolution is limited by their size. For common use as a pointer device, the dragging motion of a finger is translated into a finer, relative motion of the cursor on the screen, analogous to the handling of a mouse that is lifted and put back on a surface. Hardware buttons equivalent to a standard mouse's left and right buttons are below, above or, to reduce the depth of the pad in compact devices such as net books, beside the pad.
On some touch pads and associated device driver software tapping the pad may be interpreted as a click, and a tap followed by a continuous pointing motion can be used for dragging. Touchpad drivers can also allow the use of multiple fingers to facilitate the other mouse buttons.
Some touch pads have "hotspots", locations on the touchpad used for functionality beyond a mouse. For example, on certain touch pads, moving the finger along an edge of the touch pad will act as a scroll wheel, controlling the scrollbar and scrolling the window that has the focus vertically or horizontally. Apple uses two-finger dragging for scrolling on their track pads. Also, some touchpad drivers support tap zones, regions where a tap will execute a function, for example, pausing the media player or launching an application. All of these functions are implemented in the touchpad device driver software, and can be disabled. external image finger_610x458.jpg

Advantages and Disadvantages


  • Touch Pad devices can be custom designed to meet your requirements for size, thickness, buttons, and software features.
  • Touch Pad includes patented, advanced features, such as Hand Check, Virtual Scrolling, Tap Zones, and Edge Motion.
  • Touch Pad is resistant to moisture, dirt, and surface scratches.
  • With no moving parts to wear out over time, Touchpad devices have a related life of over 1 million taps.
  • Resolution of 1000 DPI results in a precise and responsive touching sensing.
  • Requires only a slight touch to activate, no pressure is necessary.
  • The pad's position is fixed relative to the keyboard, and very short finger movements are required to move the cursor across the display screen.
· No additional mouse needs to be carried along with the laptop every time
· Hand movements are reduced to smaller finger movements.
· Nice tricks like auto scroll on the side.

· Only available on laptops.
· Smaller surface to move on.
· Activates when your busy reading something on auto scroll and you’re your hand on it.
· Left and right keys are more difficult to use that in regular USB mouse.
· Cannot scroll across the screen in one go

Common Uses


  • Laptops
  • E-Books

Graphics Tablet

What is a Graphic Tablet?

A graphics tablet is a computer input device that allows one to hand-draw images and graphics, similar to the way one draws images with a pencil and paper. These tablets may also be used to capture data or handwritten signatures. It can also be used to trace an image from a piece of paper which is taped or otherwise secured to the surface. Capturing data in this way, either by tracing or entering the corners of linear poly-lines or shapes is called digitizing.
A graphics tablet consists of a flat surface upon which the user may "draw" or trace an image using an attached stylus, a pen-like drawing apparatus. The image generally does not appear on the tablet itself but, rather, is displayed on the computer monitor. Some tablets, however, come as a functioning secondary computer screen that you can interact with images directly by using the stylus.
Some tablets are intended as a general replacement for a mouse as the primary pointing and navigation device for desktop computers.

How does a Graphics Tablet work?


The stylus pen, or digitizer pen, is operated without the use of batteries, which allows the pen a lightweight design A graphic tablet gives power to the pen via electromagnetic waves. Because it is more natural for people to hold a pen, as opposed to a mouse, the trigger finger syndrome is removed from the computing experience. A digitizer pen with an eraser end allows the user to erase text, or even activate the eraser tool in graphics applications like Photoshop or Paint. Graphic tablets come in different levels of sensitivity to pressure applied on the surface by the digitizer pen. Applied pressure on the drawing surface of the graphic tablet gives a mark or lines its thickness. Pressing the digitizer pen hard against the drawing surface will result in the line or mark being very dark. Lightly touching the pen to the surface of the graphic tablet will result in a lighter mark or line. With pressure sensitivity the user experiences a more natural approach to drawing on a computer. Graphic tablets are able to connect to computers in a number of ways, including serial port, USB and Bluetooth. Serial ports require the tablet to have a separate power source from the computer. USB connections run electricity from the computer to the graphic tablet. Bluetooth allows graphic tablets to connect to a computer wirelessly. external image DigiPro_5.5%C3%974%E2%80%9D_Graphics_Tablet4ceDetail.jpg

Advantages and disadvantages

  • It is portable,
  • You feel more comfortable writing in your own way

  • Not always plug and play
  • Configuration and compatibility can be an issue