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How Does Projected Capacitive Touch Technology Work?

19 February 2019

Touch technology has become commonplace in human to computer interaction and is, without a doubt, one of the most definitive technologies of the digital age. This is largely down to the outstanding performance of capacitive touchscreens.

Demand for this technology continues to increase and as we’re all likely to use a projected capacitive touchscreen in the course of our working day or leisure time, it’s helpful to understand the basic principles of how they work.

What Is Projected Capacitive Touch Technology?

Prior to the release of the iPod Touch and the first iPhone, the use of projected capacitive touch technology (PCT™) was relatively small. However, since these two, milestone consumer electronic devices, this touch sensing technology has changed the way that we interact with machines of all types and in many environments. This is the technology that allows us to scroll, zoom, pinch and lightly tap on our mobile devices and is now the de facto method for controlling electronic systems as diverse as ATM’s and video jukeboxes.

The Technology Behind the Screen

Custom designed PCT™ touchscreens are fast becoming the first choice for high-tech devices. Whereas older forms of touch would use a variance in electrical resistance or breakage of light beams to detect touch, these days most touchscreen rely on the principle of projected capacitance. In essence, this is the ability of a touchscreen to carry an electric charge, and for that charge to be drawn off or changed in some way, as a finger or suitable conductive stylus or object approaches.

A projected capacitive touch screen is typically manufactured with a front layer of glass, with a matrix of conductive elements behind. These elements are made from electrically conductive materials such as Indium Tin Oxide (ITO), Silver, Copper or Carbon – and they are arrayed in an X-layer and a Y-layer (with insulation between).

The conductive matrix is connected to a suitably designed touch controller which injects an electrical charge into the matrix and then monitors the various elements of the matrix for changes. When a finger (or a stylus) approaches the front of the touchscreen, there is a minute change in the capacitive field generated within the matrix behind the front glass. The touch controller firmware should then be sophisticated and sensitive enough to detect these changes, identifying the areas or elements of the matrix with the greatest change, and ‘triangulating’ the touch position(s) within the X and Y layers. The controller then transmits this data in the form of X-Y coordinates to the host computer, much in the same way as a mouse or mouse pad (also projected capacitive touch sensing) moves a cursor around a display.

There are two types of projected capacitive touch sensing – self capacitive and mutual capacitive. Both have advantages and limitations described in detail elsewhere on our website and in various articles and whitepapers but suffice to say that the benefits of mutual capacitive touch sensing have led it to become the most widely used touch technology in the world.

What Are the Main Advantages of Projected Capacitive Touch Sensing?

Projected capacitive touch screens can provide countless benefits for a range of industries but why does this continue to be the preferred choice?

Durability

One of the major benefits of PCT screens is that they’re strong and durable. In commercial applications, it’s likely that a touchscreen will encounter a great deal of use. The function of a suitably selected and designed capacitive touchscreen won’t be affected by daily issues such as dirt and fingerprint smudges. Also, with no moving parts, no front coatings, and mounted optics/transducers (unlike all other touch technologies) – projected capacitive touchscreens should last for the lifetime of the device or system…. especially when carefully selected and designed to meet the application requirements.

Reliability

Similarly, in the unlikely event that a capacitive touchscreen is scratched, it should still continue to function as normal unless the rear mounted conductive matrix is damaged. This is because it continues to measure changes in the generated electrical field irrespective of such damage.

Natural Use

One of the main reasons the technology has been so successful in consumer electronics and now in commercial/industrial applications is because it is a highly sensitive touch technology, and yet will only react to a finger or conductive stylus (meaning ‘false touches’ are unlikely). Resistive touchscreens require considerably more pressure than a capacitive touchscreen and optical or acoustic based touchscreens can be affected by inanimate objects touching the screen (rain, leaves, neck ties, cuffs, etc.)

Image Clarity

As projected capacitive touch screens are generally produced from clear, uncoated glass, with a matrix of microscopic conductors on the rear face, they generally provide a higher quality picture than most other touch technologies. This makes capacitive screens a good choice for the latest high definition and now, UHD and OLED displays.

At Zytronic, our range of award winning, and patented projected capacitive technology (PCT and MPCT™) touchscreens offer the ultimate solution for challenging environments, especially public facing, unattended and sometimes outdoor applications such ATM’s, self-service POS, slot machines, interactive digital signage and touch tables.

Get in touch with us today to find out how we can help you.

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