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Choosing The Right Touch Screen

30 January 2018

Resistive, infra-red, surface acoustic wave, projected capacitive – with so many “flavours” of touchscreen, how do you know which is the best one for you?

There are various factors to consider when looking for a new touch sensing technology. The type of application, the surrounding environment and the required performance of the system you are designing, will greatly influence the right choice of touch technology. Picking the wrong technology can be disastrous for your kiosk, digital sign or POS terminal, leading to dissatisfied customers and ultimately, damage to your business’s reputation.

The important factors we recommend you consider are:

  • Location? Will the touchscreen be positioned be indoors or outdoors?
  • Unattended? Will the touchscreen be at risk of abuse and vandalism?
  • Environment? What kind of operating conditions will the touchscreen be expected to work in (light, weather, interference, contamination, etc.)?
  • Size? What is the optimum size for your application and how many customers could be using the touchscreen at any one time?

 

We’ll summarise the most common touch technologies, keeping in mind the factors above, to help you make an informed decision.

Resistive

Resistive touch was, in its heyday, the most widely used touch technology. A resistive touch sensor is composed of a rear glass or transparent panel and a flexible transparent plastic front screen, the inside surfaces of each covered with a thin metallic coating (usually Indium Tin Oxide, one layer of which has a small measured charge applied) and separated by a narrow air-gap created by tiny glass beads between the layers. When a user pushes the front screen with their fingers or an object, the two metallic layers make contact beneath the touch point, resulting in an electrical flow. The point of contact is detected by this change in voltage as measured and triangulated by the attached touch controller.

Advantages:

  • Can be activated with any object (finger, stylus, gloved hand, pen, credit card. etc.)
  • Mature, lowest cost, mass produced touch technology
  • Low power consumption
  • Unaffected by vibration and surface contaminants
  • Negligible electromagnetic discharge (EMI)
  • Can be fully sealed (IP65+) for water resistant applications

Disadvantages:

  • Conductive coatings lower the light transmission compared to other touch technologies
  • Outer film is vulnerable to damage from scratching, poking and sharp objects (at which point the screen stops working in the area of damage)
  • Affected by long term wear on the layers from repeated touching (causes touch ‘drift’)
  • Generally, single/dual touch only
  • Maximum size usually <20” diagonal

Best suited for attended, low cost, and low usage applications, where the possibility for damage is minimal, regular replacement is not an issue, or there is a very high electromagnetic compatibility requirement e.g. certain military (battlefield and surveillance) or critical care medical applications.

Surface Capacitive

Surface Capacitive touch sensors are created by applying an extremely thin transparent conductive layer (usually Indium Tin Oxide) to the surface of a glass panel. A very small, measured charge is applied to this layer. When an exposed finger or conductive stylus touches the screen surface, some of the electrical charge transfers from the screen to the user. This decrease in capacitance is detected by transducers located at the four corners of the screen, allowing the controller to triangulate determine the touch point.

Advantages:

  • Better image clarity than Resistive touch
  • Mature technology, widely available at a lower cost compared to many other technologies
  • Unaffected by dust and dirt on the surface
  • Sizes up to ~32”

Disadvantages:

  • Requires bare finger or capacitive stylus for activation
  • Operation affected by damage and liquids on the surface
  • Affected by long term wear on the layers from repeated touching (causes touch ‘drift’)
  • Does not support multi-touch functionality
  • Edge transducers prevent touchscreen designs from being fully-flat
  • Each touch sensor is ‘tuned’ to its own controller (making replacement costly)

Best suited for attended, indoor applications where longevity is not essential.

Surface Acoustic Wave

Surface Acoustic Wave (SAW) touch screens utilize a series of piezoelectric transducers and receivers mounted along the edges of a glass panel to create a continuous ultrasonic wave on the front surface. When the panel is touched, a portion of the wave is absorbed. This allows the transducers (connected to a touch controller) to triangulate and locate the touch point.

Advantages:

  • Can be activated by finger (gloved or ungloved), or soft-tip stylus.
  • All glass panel without conductive coatings means that image clarity is excellent
  • Unaffected by most scratches
  • Unaffected by wear over time

Disadvantages:

  • Will not activate with hard items (pen, credit card, or fingernail)
  • Water droplets may cause false-triggering
  • Solid contaminants on the screen can create non-touch areas until they are removed
  • To allow free movement of acoustic wave the edges of the screen cannot be sealed, and are therefore prone to liquid and contaminants getting into the terminal.
  • May be affected by vibration
  • Only capable of single and dual touch operation

Best suited for indoor use. Despite their high scratch resistance and durability, SAW sensors are not very well suited to outdoor applications. Their functionality can be negatively affected by weather conditions and surface contaminants.

Infra-Red

Unlike most other touch technologies, Infra-Red or “IR” touch screens do not require a touch detecting overlay covering the display front. Instead, they use IR emitters and receivers mounted within a (usually plastic) frame, attached to the display bezel. This frame creates an invisible curtain or grid of light beams across the screen, side to side and top to bottom. When any object breaks the infrared curtain, the touch controller determines the touch point based upon the X-Y position of the interrupted signal. Sometimes a protective glass or plastic screen is placed over the display to prevent touches damaging the fragile LCD surface.

Advantages:

  • Display brightness and image clarity unaffected
  • Relatively low cost and widely available technology
  • Easy integration and replacement
  • Available for very large size displays (>100”)
  • Can support multitouch operation with correct controller

Disadvantages:

  • Accidental activation easy as any object breaking the infrared beams will trigger a touch
  • Dirt and contaminants on the frame impede the light beams causing touch malfunction
  • Sensitive to interference from any ambient light containing the IR spectrum (e.g. sunlight)
  • IR frame must stand higher than the display surface, therefore fully flat designs are not possible

This technology is not well suited to unattended, outdoor applications. Performance can be greatly affected by ambient light and weather conditions.IR touch technology is more suitable for supervised, indoor applications, were a large, relatively low-cost touchscreen is required and there is less risk of frame damage/contamination.

Projective Capacitive

Projected Capacitance has overtaken Resistive as the dominant global touch technology. As with Surface Capacitive touch detection, Projected Capacitive technology relies upon a conductive object interacting with the charge carried by the screen, but it offers three primary advantages:

  1. It is less susceptible to performance degradation due to wear and tear or scratches, as the detecting layer(s) are embedded behind the front surface and away from potential damage.
  2. As the touch sensing is does not rely on a direct touch (see below), it can also be activated with a gloved hand;
  3. It is capable of true multi-touch activation (simultaneous input from more than 2 touch points). In some cases, 40 or more.

A projected capacitive touchscreen is composed of a front panel of transparent material (usually glass) with an X-Y grid of transparent electrodes deposited or laminated to the rear. When a charge is applied to these layers a three-dimensional electrostatic field is created around the touchscreen. As a finger or conductive stylus approaches the screen, there is a capacitive interaction between the contacting object and the sensor, and the touch controller triangulates the touch position within the grid by determining the point of highest change.

Advantages:

  • Depending on the conductive elements, the display brightness and image clarity remains very good
  • Excellent resistant to scratching and impact damage, especially with thicker, toughened glass variants
  • Generally, unaffected by most surface contaminants and liquids (dust, grease, water droplets)
  • Capable of working in all weather conditions when suitably designed and with a suitable touch controller
  • True multi-touch functionality available
  • Can work with gloved hands
  • Depending on the conductive materials and controller used, maximum sizes can exceed 100” diagonal.

Disadvantages:

  • Generally, more costly than other technologies
  • More sensitive to electromagnetic interference
  • More attention to integration required

Due to its proven durability and long-term reliability, coupled with total design flexibility, Zytronic’s Projected Capacitive technologies (PCT™ and MPCT™) are the ideal solution for a range of commercial applications.  Suitable for both indoor and outdoor environments and unattended, self-service equipment, the technology offers single and multitouch capability in any design and sizes from 5” to over 85”.  For two decades, Zytronic has been a global leader in Projected Capacitive touch sensing, and continues to advance the technology through patented developments and innovations such as “force” sensing, object recognition and NFC compatibility.

 

If you would like to know more about how Zytronic’s touch technology can enhance your self-service or industrial touchscreen application, please contact info@zytronic.co.uk

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