When deciding between resistive and capacitive touch, be sure to consider where as well as how the display will be used. Different use cases call for different touch technology.
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Resistive touchscreens use a relatively simple technology. A resistive touchscreen comprises two flexible sheets with an air gap between them. When the screen is touched, the sheets make contact. Then the touch location is calculated based on voltages using and an ADC. Read more about how to implement a resistive touchscreen.
Resistive touchscreens register touches made with a finger (even if gloved), stylus, pencil eraser or anything with an end blunt enough not to damage the screen. Most ATMs, card readers at the grocery store, and older home electronics (think that GPS you bought for your car in ) use resistive touch sensing.
This is our 5&#; resistive touch display. The tail from the touchscreen is visible coming down in the middle of the display and is connected to the main display tail under the black protective tape.Because resistive touchscreens are relatively simple and require only four lines to sense touch, the lines connecting the touchscreen to the microcontroller are often incorporated into the main display tail, meaning only one connection between the display module and the controller are needed.
Capacitive touchscreens are a little more complicated. Capacitive touchscreens work by registering a change in an electrostatic field on the screen when touched with an adequately capacitive object, like a finger. Gloved fingers or a stylus may be used, but they must have conductive materials to simulate a bare finger.
As capacitive touchscreens require a controller and more lines, the tail of a capacitive touchscreen is usually separate from the main display tail.
This is our 5&#; capacitive touch display. It is the same display as the display with the resistive touchscreen. On the main tail, you can see four pads where the resistive touchscreen tail would connect. To the right of the main tail, you can see the capacitive touch tail.Beyond the methods of obtaining a touch, there are pros and cons that must be considered when deciding between a resistive touchscreen and a capacitive touchscreen.
The following table compares resistive and capacitive touchscreens across a variety of categories. In short, resistive touchscreens are less expensive and work well in outdoor applications, but do not age well (they can get scratched, and become hazy with age) and can only register a single touch. Capacitive touchscreens use a glass top layer so they maintain more of the display&#;s brightness. Plus, capacitive touchscreens can support multiple touches and gestures. The main draw backs for capacitive touchscreens are the higher cost and lower tolerance of environmental factors.
Compare some of our families of displays that include a no-touch, resistive touch, and cap touch version. The 5&#; sunlight readable displays, above, start at nits and drop into the 800s.
Further, consider our 3.9&#; bar-type display. Without a touchscreen, this display boasts a respectable brightness of 500 nits. With a capacitive touchscreen applied, the brightness drops to a typical brightness of 400 nits. The brightness with a resistive touchscreen applied drops even further, to a typical brightness of 350 nits.
This is the 3.9&#; cap touch display which can recognize five distinct touches at once. The photographed display is running as part of an EVE module.https://ca.pipglobal.com/archive/literature/PIP-WP-Gloves-and-Touchscreen-Compatibility.pdf
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Kelsey is an engineer at Crystalfontz. She graduated from Gonzaga University with a BS in Electrical Engineering. Kelsey&#;s roles at Crystalfontz include customer support, documentation, product demonstrations, and design.
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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.
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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.
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.
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