Aug. 19, 2024
Capacitive touch screens were actually invented almost 10 years before the first resistive touchscreen. In the beginning PCAP were typically used more for consumer products like laptops, smartphones and tablets. Here we discuss some features that allow the new technology to overcome the past and now be the lead touchscreen for industrial applications.
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There are two options for incorporating touch controllers in the PCAP touch devices. In the first one, an Integrated Circuit (IC) controller is mounted on the surface on a separate PC board, known as Chip on Board (COB), which allows signals to be transmitted from the touch sensor through the flexible printed circuit to the PCB. Then, the IC firmware will transform the capacitance data into a digital touch position data which will be sent to the host computer. The second option is to mount the controller IC chip on the surface directly on the touch flex tail, also known as Chip on Flex (COF). In this case, an analog capacitance signal is converted into digital position data on the FPC which will be sent to the computer via serial interface.
Electromagnetic interference (EMI) noise can interfere with the accurate detection of touch events in PCAP touch screens. To maintain the accuracy of the touch detection, the PCAP touch controller leverages firmware and hardware to avoid noise interference at different frequency bandwidths.
On certain industrial applications, water can accumulate on top of PCAP touch screens and trigger false touches. To avoid those false touches, the latest PCAP technology features water repellent surface treatments and a firmware algorithm to differentiate an actual touch from water droplets. These new features enable the touch screens to work flawlessly with challenging operating conditions.
The improved algorithm on PCAP touch controller firmware enables the touchscreen manufacturer to be able to tune the projection field for different applications, thus enabling workers to keep their thick working or safety gloves on while operating on their HMI equipment.
To improve precision, certain PCAP touch screens now include a thicker glass which will detect fewer signals while increasing the signal strength and maintain an optimal noise ratio.
Selecting the most suitable type of touch screen for your project can improve device functionality and durability, which can mean a significant increase in customer adoption.
How can you choose which touch screen option best aligns with your needs?
This article highlights the unique advantages and drawbacks of common touch screen technology, to help product design engineers make an informed decision.
Resistive touch is a legacy form of touch screen technology that was broadly popular for many years, but has been replaced by capacitive touch for many applications. Currently, resistive touch has a smaller range of common uses, but can still capably address certain needs.
How do resistive touch screens work?
The core elements of a resistive touch screen are two substrate layers, separated by a gap filled with either air or an inert gas. A flexible film-based substrate is always used for the top layer, while the bottom layers substrate can be either film or glass. A conductive material is applied to the inner-facing sides of the substrate layers, across from the air gap.
The resistive touch screen has only two states of operation: touched and not touched.
When a user applies pressure to the top surface, the film indents and causes the conductive material on the top layer to make an electrical contact with the conductive surface of the bottom layer. This activity creates a difference in voltage that the system registers as a touch. The location of this contact is pinpointed on the X and Y axes, and the touch controller then interprets the action. Because physical force is needed for a resistive touch screen to function, it is similar to a mechanical switch.
Resistive touch screens must be calibrated before they are used to ensure accurate and reliable operation. A user must apply pressure to the four corners of the screen, and sometimes on its center, to calibrate the screen with the rest of the system via a lookup database.
Advantages of resistive touch screens
Because resistive touch screens interpret physical pressure as a touch, they are effective in a variety of environments using single touch. Any object capable of applying force to the screen can be used with the same result. For example, in applications where end users wear gloves, resistive touch screens offer reliable single-touch functionality.
Since resistive touch screens area actuated via mechanical force, they continue to function as intended even when liquids or debris are present on the surface. This makes them especially useful in situations where substances could disrupt the function of other types of touch screens. For example, on single-touch applications within agricultural equipment, boats and underwater machinery.
Besides the functional advantages of resistive touch screens, price is a common reason why OEMs select this option. In projects where cost is a top concern, companies can use this option to realize savings that may not be possible with alternatives.
Disadvantages of resistive touch screens
The configuration of a resistive touch screen removes the possibility of gestures, such as pinching and zooming, or any actions requiring multi-touch functionality. These screens cannot determine the location of a touch if more than one input is present.
In terms of visibility, the film substrate commonly used as the top surface in resistive touch screens is less transmissive than glass. This leads to reduced brightness and a certain level of haze compared to touch screens with a top layer of glass. The film layer can also expand or contract based on temperature, which alters the distance between the two layers and affects touch accuracy. Additionally, the film substrates are susceptible to scratches and can start to wear away with repeated use, necessitating occasional recalibration or replacement over time.
Capacitive touch screens were invented before resistive touch screens. However, early iterations of this technology were prone to sensing false touches and creating noise that interfered with other nearby electronics. Due to these limitations, resistive touch screens and other options, like infrared touch screens, dominated the industry.
With more development and refinement of controller ICs, projected capacitive (PCAP) touch screens became the preferred touch technology for a majority of applications. For example, this technology is now commonly used on tablets, laptops and smartphones. Though PCAP stands for &#;projected capacitive (PCAP) touch&#;, it&#;s more commonly referred to as &#;capacitive touch&#;.
How do PCAP touch screens work?
The foundation of PCAP touch screens is an array of conductors that create an electromagnetic field. As a user touches a PCAP screen, the conductive finger or object pulls or adds charge to that field, changing its strength. A touch controller measures the location of this change and then instructs the system to take a certain action, depending on the type of input received.
For a device with PCAP touch technology to acknowledge an input, users simply need to touch the screen. No physical pressure is required, unlike resistive touch screens.
Another key difference from resistive touch technology is that PCAP screens can accommodate a variety of inputs, with different gestures and more contact points instructing the system to take a variety of actions. PCAP touch can support multi-touch functionality, swipes, pinches, and zoom gestures which aren&#;t possible with resistive touch screens.
A PCAP touch screen is very similar to a solid state switch, as its mechanism of action requires a change in the electrical field over a control point.
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Further reading:Advantages of PCAP touch screens
The value that comes with recognizing multiple inputs is a clear and positive differentiator for PCAP touch screens. Users can initiate a variety of commands, providing more functionality in devices where this technology is used. Consider how consumers now expect smartphones, tablets, and interactive laptop screens to support actions requiring two fingers, like pinching and zooming. In more specialized settings, such as multi-player gaming applications, PCAP touch screens can support more than 10 inputs at a single time.
PCAP touch screens do not require initial calibration, offering a simpler experience than resistive touch screens. Additionally, PCAP touch screens are highly accurate even as they support a variety of gestures and subsequent actions by the system.
Since their top layer is usually made of glass, PCAP touch screens offer a high degree of optical transmission and avoid the appearance of haze to users. Additionally, the glass top layer provides improved durability compared to the film top layer of resistive touch screens &#; even for the largest sizes of up to 80 inches (and growing).
Operation in environments where a PCAP screen may be exposed to liquids or moisture &#; including conductive liquids like salt water &#; is possible through specialized controller algorithms and tuning. PCAP technology has evolved to support medical glove and thick industrial glove operation, as well as passive stylus operation.
PCAP touch screens can be customized with different cover lens materials (soda lime, super glasses, PMMA) based on application specific needs. Cover lenses can be ruggedized with chemical strengthening and substrates that improve impact resistance. This can be especially valuable for public-facing applications, like ATMs, gas pump displays, and industrial applications. Specialized films or coatings &#; such as AG (anti-glare), AR (anti-reflective), AF (anti-fingerprint) &#; can be added to the cover lens substrate to improve optical performance.
Disadvantages of PCAP touch screens
Unlike resistive touch screens, PCAP touch screens depend on variations in an electrical field to operate. While a passive stylus can activate this screen, a non-conductive tool like a pencil can&#;t.
If cost is a top concern for a project, PCAP may not align with budget limits. It is a more expensive technology than resistive screens, although it continues to grow more accessible in terms of price as the technology advances and improves.
Summary: PCAP vs. resistive touch (comparison table)
The below table compares the advantages and disadvantages of projected capacitive touch vs resistive touch screens.
CharacteristicsPCAP TouchResistive TouchRequires calibrationNo
Yes
Single-touchYes
Yes
Multi-touchYes
No
Passive stylus & glove operationYes
Yes
Operation with non-conductive object such as a pencilNo
Yes
Moisture immunityYes
Yes
Optical TransmittanceHigh
Hazy
DurabilityHigh
Low
Cost$$$
$
Working with New Vision Display
As a leading manufacturer of touch and display products, New Vision Display can help you determine the specific needs of your project and tune your PCAP touchscreen controllers to meet them. Our PRECI-Touch® products are based primarily on PCAP touch technology and can be customized for a variety of applications using a wide range of materials, stacks, and controllers.
Whether your product will be used in a life-saving medical device, the center console of an automobile, or the navigation controls on a yacht &#; we can deliver an effective solution for your application. To get started on your project, contact our specialists today.
For more Resistive Touch Screens Chinainformation, please contact us. We will provide professional answers.
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