What is meant by an embedded display?
A screen that links to an embedded device is known as an embedded display. The screen displays information about the device and allows people to interact with it. These displays, also known as embedded touch screens, allow users to interact with the device by touching the screen's surface. Smartphones, such as the iPhone, were among the first to make use of this technology.
A Liquid Crystal Display (LCD) could be one of the fundamental standard screens for embedded systems. Character LCD and Graphic LCD modules are the two types of LCD modules used in embedded systems. A character LCD simply displays characters and is the most basic and inexpensive LCD technology. A graphic LCD is more sophisticated and can display images.
Most integrated designs on the market today, ranging from consumer white goods to industrial gear, have some type of display. The current sophistication of touch displays, which allows commands to be conveyed via swipes and gestures, owes a great deal to the early smartphone designers. Touch-enabled LCD displays can save money by eliminating the requirement for switches and push buttons. Using capacitive touch screens to prevent dust and moisture infiltration through switch casings can help increase product durability. Furthermore, a well-presented, visually appealing, and intuitive display contributes greatly to a product's aesthetics, boosting product brand value, and user confidence.
Another option is to use a separate display controller. The majority of the aforementioned resources are incorporated on-chip, including frame buffer memory and a microcontroller. Furthermore, the use of industry-standard connectors allows for a simple interface to the host MCU. This has the advantage of freeing up resources for the program by offloading display responsibilities.
Touchscreen technologies with distinct touch sensing modalities include resistive, capacitive, projected capacitive, scanning infrared (IR), and surface acoustic wave (SAW). The correct touch technology for a certain application necessitates a study of each type. All touchscreens are composite components that include a touchscreen overlay as well as an information-processing controller. Some technologies are explained as follows:
● Resistive Technology: The most common touch technology nowadays is the five-wire resistive touchscreen. A resistive touchscreen panel is made out of a glass panel that is covered with thin conductive and resistive metallic layers separated by a thin gap. So when you touch the screen, two layers make contact. The computer detects changes in the electrical field and calculates the touch point. Resistive touchscreens are often the cheapest, however, they only provide 70% to 85% visual clarity.
● Super Capacitive Technology: A surface-capacitive touch panel detects current. On top of the glass substrate, a protective cover is applied over the transparent electrode film. Voltage is provided to all four corners, and any contact with the surface causes the current to be disrupted. As a result, the controller determines the touch point. It is most commonly found in the gaming business. Furthermore, light transmission averages 80% or higher.
● Projected Technology: Projected capacitive technology is the market's new powerhouse. This technology is mostly found in iPhones and iPads. The electronic field is projected through the top of the glass with this technology, causing energy to form an electrostatic field. As a result, whenever there is a change on the surface, a change in the electrodes is detected, which further calculates the contact point.
Ideally speaking, a touch screen shall have the following specifications:
It should not damage the display image because it is stacked on top of it.
Its resolution should be the same as the video display.
Activation is irrespective of stylus size, conducting or non-conducting nature of styli, and gloved or ungloved finger touch.
It can provide the operator with positive, tactile feedback.
The architecture should be modular and adaptable to additional input devices and networks.
The human perspective has been given due consideration, with factors like ergonomics, cognitive psychology, and human physiology taken into account.
Target selection must be exact to avoid unintentional selection of adjacent targets.
It is resistant to dust, grease, moisture, pressure, vibrations, and chemical or oil vapors in the environment.
There is practically no perfect screen that can have all the above features. However, the following are some considerations that you shall make before selecting a touch panel for your embedded device.
● How will it impact your device: If you incorporate a display into your design, the specs of your embedded device are likely to grow. This is due to the need for additional RAM to be allocated for the display frame buffer. A video controller is already built into some screens. This can read data from the display buffer and write it on the display. Others, on the other hand, do not. This adds additional overhead to the MCU. The primary function of an embedded device is often to manage the core application. The additional requirements and memory are due to the fact that it must run the display and frame buffer duties on top of this.
● How complex and long is the design cycle: As you are surely aware, building and testing remote display solutions is frequently more difficult than anticipated. Unexpected hitches and hurdles must frequently be overcome. When creating from scratch, the display hardware should be organized around the core application, and everything should be debugged and tested. In this circumstance, what is the typical design cycle? A period of 4 to 6 months is not unreasonable. This is when an alternate route may be worth investigating to alleviate tensions and lengthen the design cycle. To begin, off-the-shelf display modules often include a driver, primitives, and GUI functions that have already been tried and proven. If you have the money, it might be worth skipping class and taking this route. On the other side, you may be wondering if it's actually worth having a display on your embedded design at this time.
● Touch type: Capacitive projection is suited for severe, industrial, and outdoor applications. For such purposes, the IR type will not suffice. If image clarity is critical, IR will be a better alternative, despite the increased cost.
● Bonding type: Direct sunlight or high-brightness applications can cause glare and reflection on TFT LCD monitors. Almost all TFT LCDs have an air gap between the cover lens and the TFT screen. When used in high-brightness installations, an air gap creates repetitive refraction between each component level of the display. Reducing reflection inside these components with bonding increases contrast and makes the screen more readable in outdoor or high-light circumstances without increasing the panel's brightness. There are two types of bonding, i.e. optical and air. Due to the harsh environments, optical bonding is used in the military, marine, medical, transportation, and retail sectors, where a higher-performing display is required. Optical bonding is well suited to companies that use tough displays in high-reliability situations or industries where displays must be viewable in bright sunlight. Air bonding is good for indoor applications and is less costly.
● Surface treatment: You need to consider if the touch panel should have surface treatment, depending on the application. When directly touching the display, anti-fingerprint (AF) surface treatments reduce fingerprint marking. This is frequently coupled with a touch panel. The anti-bacterial (AB) surface treatment is applied to the cover glass as a coating. In the medical field, nano-silver technology is commonly employed, and when paired with a SiO2 layer, it breaks down the bacterial cell wall and lowers bacterium reproduction by 99.999%. The anti-glare (AG) surface treatment is a low-cost way to reduce glare and undesired reflections. Under typical conditions, light reflects in a predictable manner. This can be specular or diffused.
● Water and dust resistance: Depending on the application, you should consider whether you need a water and dust resistance panel or not. The sealing of the sensor face and housing against dust, grime, and moisture is referred to as waterproof displays or touch screen monitors. An Ingress Protection (IP) rating, such as IP-67, is a typical standard used to identify the quality of the equipment seal. A good seal does not guarantee that the item will work in water. Most late-generation smartphones with PCAP touch screens, for example, are now waterproof. It can be submerged, fished out, dried, and used again. However, you cannot use the touch screen when it is submerged.
● Screen size: Touchscreens are offered in three sizes: small, medium, and large. Touchscreen monitors typically range in size from 8.9cm to 1.3m (3.5-inch to 52-inch). For big control rooms, the most typical sizes are 38.1cm to 48.2cm (15-inch to 19-inch) and 81.2cm to 1.1m (32-inch to 42-inch). There are additional large displays available up to 2.5m (100-inch). The aspect ratio (4:3 or 16:9) should also be taken into account.
● Accuracy of touch: This is the capacity of a touch sensor to provide dependable touch performance in devices when it is subjected to high levels of noise from sources such as screens and chargers. You must be able to choose targets accurately on touchscreens while avoiding the unintentional selection of adjacent targets.
● Resolution: It refers to the touchscreen's resolution or the number of touch-active points. It has an impact on pointing precision and selection errors. As a result, a higher-resolution screen gives more touch points, allowing for more pointing. Another resolution (pixel density) to consider is the display resolution, which might be HD, full HD, and so on.
● Response time: The shorter the time between a touch and a reaction, the more satisfied you will be with the touch system. It is measured in milliseconds (ms). Latency is normally between 75ms and 100ms. According to studies, humans require less than 10ms of comfort. SAW touchscreens have a response time of about 10ms, whereas IR has a response time of about 20ms.
● Clarity: Touchscreens are typically placed on top of the display, causing light loss and a reduction in image clarity. However, because IR touchscreens have no overlay, transmission is 95% to 100% and clarity is the greatest. This property has the lowest grade for the resistive kind.
● Life expectancy: Performance degradation is to be expected due to the constant use of the screen. The life of an IR type is around five years, but the life of a capacitive type is approximately two years.
● Robustness: The top layer of the screen must be strong enough to withstand scratching. To prevent the intrusion of water and chemicals, the assembly must be properly sealed.
Touch screens have revolutionized the use of embedded devices over the past decade and will continue to do so with this pace of scientific development. However, it is necessary to select the right display for your device to bear fruitful and desired results. Hence, the considerations discussed in this article shall be considered before selecting a touch display for your embedded device.
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