Comparision of different Touchscreen Technologies used in Electronic Devices

With the growing popularity of HMI products I keep hearing about the various technologies implemented in touch screens. How many different types of touch screens are there? What are the differences?

The first ever touchscreen was developed by E.A Johnson at the Royal Radar Establishment, Malvern, UK in the late 1960s. Evidently, the first touchscreen was a capacitive type; the one widely used in smart phones nowadays. In 1971, a milestone to touchscreen technology was developed by Doctor Sam Hurst, an instructor at the University of Kentucky Research Foundation. It was a touch sensor named ‘Elograph’. Later in 1974, Hurst in association with his company Elographics came up with the first real touchscreen featuring a transparent surface. In 1977, Elographics developed and patented a resistive touchscreen technology, one of the most popular touchscreen technologies in use today.

Touch Screens have become very commonplace in our daily lives: cell phones, ATM’s, kiosks, ticket vending machines and more all use touch panels to enable the user to interact with a computer or device without the use of a keyboard or mouse. But did you know there are several uniquely different types of Touch Screens? The five most common types are: 5-Wire Resistive, Surface Capacitive, Projected Capacitive, SAW (Surface Acoustic Wave), and Infrared.

A touch screen has the ability to detect a touch within the given display area. It is made up of 3 basic elements, a sensor, a controller and a software driver. All the variants of touch screen technology carry their own distinctive characteristics, with individual benefits and limitations.

Resistive Touch

5-Wire Resistive Touch is the most widely used touch technology today. A resistive touch screen monitor is composed of a glass panel and a film screen, each covered with a thin metallic layer, separated by a narrow gap. When a user touches the screen, the two metallic layers make contact, resulting in electrical flow. The point of contact is detected by this change in voltage. Resistive touch screen can be divided into 4, 5,6, 7 or 8-wired models, which differentiate between the coordinates of touch.

As one of the most commonly used, resistive touch screen relies on a touch overlay, constructed by a flexible top layer and rigid bottom layer, divided by insulating spacer dots. The inside surface is coated with a transparent material (ITO) that makes electrical contact when pressure is applied. These voltages are then converted to X and Y coordinates, which are sent to the controller.

Resistive touch screen panels are generally more affordable but offer only 75% clarity and the layer can be damaged by sharp objects

Advantages:

•  Can be activated with virtually any object (finger, stylus, gloved hand, pen, etc.)

•  Has tactile feel

•  Lowest cost touch technology

•  Low power consumption

•  Resistant to surface contaminants and liquids (dust, oil, grease, moisture)

Disadvantages:

•  Lower image clarity compared to other touch technologies

•  Outer polyester film is vulnerable to damage from scratching, poking and sharp objects

Surface Capacitive

Surface Capacitive are the second most popular type of touch screens on the market. In a surface capacitive touch screen monitor, a transparent electrode layer is placed on top of a glass panel, and covered by a protective cover. When an exposed finger touches the monitor screen, it reacts to the static electrical capacity of the human body; some of the electrical charge transfers from the screen to the user. This decrease in capacitance is detected by sensors located at the four corners of the screen, allowing the controller to determine the touch point. Capacitive touch screens can only be activated by the touch of human skin or a stylus holding an electrical charge.

Advantages:

•  Better image clarity than Resistive Touch

•  Durable screen

•  Excellent resistance to surface contaminants and liquids (dust, oil, grease, water droplets)

•  High scratch resistance

Disadvantages:

•  Requires bare finger or capacitive stylus for activation

•  Sensitivity to EMI/RFI 

Projected Capacitive

Projected Capacitive is similar to Surface Capacitive, but it offers two primary advantages: in addition to a bare finger, it can also be activated with surgical gloves or thin cotton gloves; and it enables multi-touch activation (simultaneous input from two fingers). 

A projected capacitive is composed of a sheet of glass with embedded transparent electrode films and an IC chip, which creates a three dimensional electrostatic field. When a finger comes into contact with the screen, the ratios of the electrical currents change and the computer is able to detect the touch points.

Advantages:

•  Excellent image clarity

•  More resistant to scratching than Surface Capacitive

•  Resistant to surface contaminants and liquids (dust, oil, grease, moisture)

•  Multi-touch (two-touch)

Disadvantages:

•  Sensitive to EMI/RFI

•  Must be activated via exposed finger, or thin surgical or cotton gloves

SAW Touch

SAW (Surface Acoustic Wave) touch screen monitors utilize a series of piezoelectric transducers and receivers along the sides of the monitor’s glass plate to create an invisible grid of ultrasonic waves on the surface. When the panel is touched, a portion of the wave is absorbed. This allows the receiving transducer to locate the touch point and send this data to the computer. SAW monitors can be activated by a finger, gloved hand, or soft-tip stylus. SAW monitors offer easy use and high visibility.

Advantages:

•  Excellent image clarity

•  Even better scratch resistance than capacitive

•  High “touch-life”

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

Infrared (IR) Touch

Infrared touch screen monitors do not overlay the display with an additional screen or screen sandwich. Instead, a frame surrounding the display consists of LEDs on one side and phototransistor detectors on the other. The phototransistors detect an absence of light and relay a signal that determines the coordinates. The touch is identified and located at the point of interruption of the LED beams.

Infrared monitors use IR emitters and receivers to create an invisible grid of light beams across the screen. This ensures the best possible image quality. When an object interrupts the invisible infrared light beam, the sensors are able to locate the touch point.

Advantages:

•  Highest image clarity and light transmission of all touch technologies

•  Unlimited “touch-life”

•  Impervious to surface scratches

Disadvantages:

•  Accidental activation may occur because the infrared beams are actually above the glass surface

•  Dust, oil, or grease buildup on screen or frame could impede light beam causing malfunction

•  Sensitive to water, snow, rain

•  May be sensitive to ambient light interference

•  Higher cost

source: www.TRU-VuMonitors.com


Below is the comparision of 3 touch screen technologies -Resisitive, Capacitive, Infrafred in reference to mobile: