Touch Panels

Selectronic can supply touch panels together with TFT displays or supplied separately according to your project’s needs.

Selectronic work together with our customers and the LCD and TFT manufacturers to offer the best technical and cost effective solution for each application.

Whilst most touch screen solutions are designed together with the LCD/TFT, separate touch screens can be offered depending on the application and requirements.

Please contact us at Selectronic to discuss your requirements.

Touch Screen Technologies

Touchscreens are now a way of life for most people and we use them every day from smart phones to ATM’s and the Central Information Displays in our cars.

All of these applications (plus many more) show the user the information they need via the display unit (i.e. the LCD/TFT). The user can react to the information displayed and can change the required information via the touchscreen mounted in front of the display.

Many different technologies of Touchscreens exist, but the most common are as follows:

  • Resistive
  • Capacitive (surface capacitive and projected capacitive, and new ‘in-cell’)
  • SAW Surface Acoustic Wave
  • Infrared

The selection of a specific touch technology depends on the requirements of the individual applications together with the the ambient conditions.

Resistive Touch Screens

resistive-touch-panels  

Resistive touchscreens consist of two ITO (indium-tin oxide) layers, thinly and uniformly sputtered onto both the glass and PET (Polyethylene terephthalate) layer. Tiny bumps (spacers) are then added to the glass side on top of the resistive ITO coating, to keep the PET film from sagging, causing an accidental or false touch. If the surface is touched at a particular location, this creates a contact between the two ITO layers. The used controller calculates the X and Y co-ordinates touched at the contact position.

Advantages:

  • Most common type of touch screen on the market
  • Relatively low cost
  • Operated in many ways – by finger, pointer, medical glove, work gloves…..
  • Can work in harsh ambient environments

Disadvantages:

  • Top sheet is highly susceptible to scratches/cuts etc.
  • Layer is a flexing mechanical element coated with a conductive material which wears with every flex
  • Transmission typically 80%
  • Requires calibration

Capacitive Touch Screens - Surface capacitive

capacitive-touch-panels

In this basic technology, only one side of the insulator is coated with a conductive layer. A small voltage is applied to the layer, resulting in a uniform electrostatic field. When a conductor, such as a human finger, touches the uncoated surface, a capacitor is dynamically formed. The sensor’s controller can determine the location of the touch indirectly from the change in the capacitance as measured from the four corners of the panel.

Advantages:

  • Can withstand contaminants such as grease and harsh chemicals
  • Long life expectancy – over 225 million touches (50 million in one location)
  • Transmission typically 90%
  • Fast response time

 

Disadvantages:

  • Can only be used with ‘ungloved’ finger or attached stylus

Capacitive Touchscreens - Projected Capacitive

 

Projective capacitive touch (PCT or PCAP), permits more accurate and flexible operation, by etching the conductive layer. The functional principle is based on an arrangement of capacitors which are distributed across an active surface in X and Y directions. In a non-operated state, each of the capacitors has a known property. The operating element (finger, stylus) invades the capacitor’s field as a disturbance and changes its capacity. The connected touch controller detects the change of the related capacitor(s) and provides the appropriate operating position. A high resolution of the detected position is possible through the interpolation of a number of these capacitors.

Advantages:

  • Can withstand contaminants such as grease and harsh chemicals
  • Works with fingers, certain types of gloved hands or conductive stylus
  • Fast response time
  • Works even if glass is scratched or broken
  • Multitouch possible

Disadvantages:

  • More complex design
  • Higher cost

Capacitive Touch Screens - In Cell

capacitive-in-cell-touch-panels

“In-cell” touch panels share the same conductive layer in the thin film transistors (TFTs) used to switch the display’s sub-pixels on and off. (These transistors are fabricated directly on the semiconductor backplane of the display).
This type of touchscreen reduces the visible distance between the users fingers and what the user is touching on the screen, creating a more direct contact with the content displayed. This enables the touch to be more responsive, and reduces the overall thickness of the display/touch solution.

Advantages:

  • Reduced thickness of total solution
  • Better colour saturation as light has less layers to pass through
  • Lower cost than surface capacitive

Disadvantages:

  • LCD Manufacturers may need to offer 2 solutions – one with touch and one without, or in-cell may be offered for custom projects only
  • Higher cost than 4wire resistance touch

Surface Acoustic Wave Touch Screens

surface-acoustic-touch-panels  

With Surface Acoustic Wave (SAW), piezoelectric transducers located at different positions of the screen are used to turn the waves of mechanical energy of a touch (vibration) into an electronic signal. The waves are spread across the screen by bouncing off reflector arrays along the edges of the overlay and are detected by ‘receivers’. The acoustic wave weakens when the user touches the glass. The coordinates are then determined by the controller that measures the time at which the amplitude declines.

Advantages:

  • Works with fingers, gloved hands and soft stylus (not a hard stylus)
  • No touch overlay or coating required, so no layers can be worn
  • No brightness or contrast loss

Disadvantages:

  • Can be affected by dirt/dust and or water, if not sealed
  • Display surface needs to be lower than the mounting bezel

Infrared Touchscreens

infrared-touchscreen

Infrared technology relies on the interruption of the IR light grid in front of the display screen. The touch frame contains a row or IR LED’s and photo transistors, each mounted on two opposite sides to create a grid of invisible infrared light. When touching the screen, one or more of the beams are obstructed resulting in X and Y coordinates being sent to the control unit to indicate the exact touch point.

Advantages:

  • No overlay so 100% light transmission (protective glass optional)
  • Withstands severe environments
  • All kinds of input stylus can be used, finger, gloved hand etc.
  • Multitouch possible

Disadvantages:

  • False/unintended activation possible due to IR light beam above the surface of the display
  • Dirt/dust build up on frame may also cause false activation

Contact Selectronic Today

Bespoke-Designs  

Make the first step in taking your idea to reality by contacting our team. We love to hear new ideas, and innovation is our heartbeat. With our experience and extensive knowledge we can help you every step of the way.

Use the form below to contact us or call +44 (0)1993 778000 to talk to one of our team.

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