Smartphones typically have an LCD graphical screen with touch input.  Touch is used to take user input via windows controls such as menus and command buttons.  A SIP (Software Input Panel) may also be used am on-screen keyboard.  Alternatively, some phones use a small physical keyboard.  Some use both.  Most touchscreens are single input, that is only one point of contact can be deciphered.  Multitouch is becoming a required feature.  Multitouch allows not only simple zoom and rotation of images, it allows quite complexes gestures.  Windows 7 supports Multitouch with suitable hardware. 

A touchscreen has two uses.  One is as a pointing devices, that is as a mouse.  The other is to action gestures such as click, double click etc,  It can be used with a finger or stylus.

Windows CE can support an LCD panel with a touchscreen; it has for many versions.  Windows CE 6 R3 supports single finger gestures.  My HTC phone (HTC HD2) support Multitouch, event though it’s Windows Mobile 6.53, which is CE 5 based, doesn’t intrinsically support it.  My guess is that the next version of CE will support Multitouch.  Windows Phone 7 requires Multitouch, but that is is based upon CE 6 R3  (my guess). ????


The task for a touch screen is to determine the X-Y coordinates of the touchpoint (or touch points).

  • The basic touchscreen is RESISTIVE.  It scans the surface using resistive technology. When an object, such as a finger, presses down on a point on the panel's outer surface the two metallic layers become connected at that point: the panel then behaves as a pair of voltage dividers with connected outputs.  Such screens only support single touch.    Many such devices are 4 wire, others are 5 wire.  5 wire have a much longer lifetime because of redundancy (eg 32x).
  • Many touchscreens are CAPCITIVE: As the human body is also a conductor, touching the surface of the screen results in a distortion of the body's electrostatic field, measurable as a change in capacitanceThese are multitouch as used in more recent mobile phones.
  • Other types:
    • Acoustic Wave
    • Optical Imaging
    • Dispersive signal technology

Ref: http://en.wikipedia.org/wiki/Touchscreen

LCD Screens

LCD = Liquid Crystal Display

Standard LCDs use a matrix of polarization cells that electrically control whether light is transmitted.  There are reflective and transmissive LCD panels.  The reflective type use the least energy as they use the reflection of ambient light (light) (or non-reflection: dark) to create an image.  They are quite viewable in sumlight, as per a digital watch.  Transmissive LCD panels use a backlight to generate light that is either transmitted or not.  Colored displays have a combination of primary colors.  Transmissive LCD panels require more energy, but not as much as a Plasma display!

Ref: http://en.wikipedia.org/wiki/Liquid_crystal_display


New LCD displays are based upon LEDs and are much more efficient.
Organic Light emitting Diode (OLED),

Ref: http://en.wikipedia.org/wiki/Oled






CE Touchscreen driver