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Displays in Internet of Things

Figure 1. Recent studies show that around 2/3 of companies currently use the IoT, source: forbes.com

Nowadays there are two main branches of IoT development. The first is customer applications, e.g. ‘smart house’ solutions, where we have several connected devices that can be managed via a mobile application. The second is IIoT (Industrial Internet of Things) – industrial solution for managing and optimizing production.

It is estimated that in 2018 we will record about 20 billion devices operating globally as IoT solutions. Market forecasts prepared by IDC (International Data Corporation) show that investments in equipment used for Internet of Things will increase over the next few years. Estimated global expenditures in 2018 may reach up to 772.5 billion USD, which means a 14.6% increase compared to 2017.

For most IoT applications, you need a suitable display. Depending on the needs of the application, an environment in which the final device will be installed or energy consumption, we have several different technologies at our disposal. To facilitate the selection, below we present three most popular options with their advantages and disadvantages.

TFT LCD – rich content, fast refresh

Figure 2. The Internet of Things application using the TFT LCD display

LCD TFT technology thanks to many advantages (e. g. fast response time) is used mainly in customer solutions. Efficient display of dynamic, colorful content, allows you to use it in applications, where multimedia is in the first place. The downside of this technology is the high energy consumption. Due to its construction, TFT LCD are the least energy-efficient devices among possibilities presented in the article.

There are many examples of consumer use of LCD dispalys. Some of them are household appliances, such as sart washing machines or refrigerators, various types of controllers, e.g. a thermostat built into the wall or wearable devices (like smartwatches). The Internet of Things in connection with TFT LCD can be used wherever we have access to permanent power supply or where the user don't mind more frequent charging of the device.

LCD TFT displays have a built-in backlight, so they can be used in places where ambient light is dim or where mounting additional lighting is not possible. On the other hand, the use of TFT LCD display in direct sunlight is problematic due to the need to mount a stronger backlight, so that the reflected light has a lower value than the light emitted by the TFT module. This solution may negatively affect the thickness of the display and increase the energy consumption of the device, and thus the cost of use.

OLED - perfect colors, full viewing angles

Figure 3. IoT application using OLED display

Due to the lower prices in relation to previous years and many constructional advantages, OLED displays are more common on the market today. Additional advantages, in comparison to mono LCM modules, are: higher contrast, faster reaction time, full viewing angles and lower energy consumption. Increased energy efficiency is achieved thanks to use of an organic substance which emits light itself, so OLED displays do not require an additional layer of the backlight. This solution not only improves the economics of use, but also significantly reduces the thickness of the display, and thus the entire end device. In this technology, the source of the pixels itself are the source of the emitted light. Very high contrast ratio is achieved by turning off the appropriate pixels and thus obtaining perfect black.

Another advantage, that TFT displays do not have, is possibility to apply an organic substance to a plastic substrate. This is the way of creating flexible displays, that can be adapted to the housing of the end device. You can find them in smartphones, smartwatches, or smart glasses. Unfortunately, the OLED technology is still a relatively costly solution for many manufacturers. The price of OLED modules is still higher than LCD TFT displays, while energy efficiency depends on the brightness and color of the displayed content. The most optimal are images with a black background and bright elements.

EPD - high energy savings, imitation of paper

Figure 4. IoT application with e-paper display

Figure 5. IoT application with e-paper display

Internet of Things applications are usually battery powered, so energy efficiency is often a key point when choosing components. E-paper technology (EPD, Electronic Paper Display) is an excellent choice in terms of low power consumption. Its operation is based on bistability, which means that the required power is consumed only when the content is refreshed or changed.

EPD's are made to imitate traditional paper. Unlike TFT LCD and OLED modules, e-paper is perfectly readable even in direct sunlight. On the other hand, the lack of backlight may become problematic in a situation when we want to use this technology in poorly lit places. You can consider adding a backlight to the module, but you have to remember that this solution will increase energy consumption.

The most popular EPD modules are black and white ones. However, if in a given application it is important to highlight a part of the displayed information, using the version with an additional third color (red or yellow) is worth considering. These types of panels are ideal for use as e-prices.

EPD displays are gaining popularity. In addition to the consumer market (e-readers, smartwatches), they are used in industrial applications (e.g. e-prices, e-badge, smart work time registration systems) and in digital signage (information boards at bus stops, e-posters, systems for navigation inside buildings), and even in architecture, as decorative elements (e.g. E Ink Prism). Wherever you do not need to additionally illuminate the display, where energy efficiency is important, and content refreshing is relatively rare.

Selection of the display technology for the application

Proper use of IoT technology can reduce overall operating costs, help increase productivity and create additional revenue through the emergence of new markets and products. IoT is very present in applications related to home automation (smart home) and medical or automotive industry. When choosing the right display technology for the Internet of Things application, first you have to determine what factors play the most important role in a specific device. If, for example, we plan to create a passenger information system, e-paper can be an excellent choice due to energy efficiency, static content displayed and unlimited viewing angles. However, in consumer devices, such as smart refrigerators and washing machines, OLEDs and TFT LCD are perfect. Table 1 shows the most important features of the displays and their technical capabilities it will certainly help when planning a new application.

Table 1. Comparison of TFT LCD, OLED and EDP technologies for Internet of Things

Feature TFT LCD OLED E-paper
Energy efficiency Relatively small Medium Very high
Access to power Permanent access to power is required Permanent access to power is required Power needed only while changing the displayed content
Readability in sunlight Special filters and strong backlight needed Special filters needed Very good
Readability in low outdoor lighting Good Good Additional backlight needed
Contrast Good Perfect Very good
Viewing angles Limited Unlimited Unlimited
Refresh / matrix reaction time Fast Fast Limited
Preferences for displayed content Dynamic content Dynamic content Static content
Temperature resistance Standard from -20 to +70 °C Standard from -30 to +80 °C Standard from 0 to +50 °C (working range below 0 °C is available by using a special control mode)

For the purposes of the article, we have prepared a simple IoT application using an e-paper display, WiFi modules and environmental sensors.

If you want the details, please click HERE.

 Uni's Guide