How to choose the right display technology for IoT devices

Jacktang

How to choose the right display technology for IoT devices [Copy link]

Forecasters assure us that the Internet of Things (IoT) is going to be big, with billions or even tens of billions of devices connected to the networks that make up the Internet over the next decade. These “things” are inherently diverse: IoT is used as a phrase for everything from a wearable fitness band that reports your health status daily to your phone, to an embedded sensor that scavenges energy in the environment and occasionally relays small amounts of data to a server via a low-energy mesh network. Choosing
　　the “right” display for such a diverse set of applications means going back to first principles; understanding the requirements of each application, and then finding a display that best meets those needs. However, that’s not to say there aren’t opportunities for the process to go the other way around — specific display technology characteristics create opportunities for adding functionality to existing IoT devices.
　　Consider an IoT device such as the environmental sensor mentioned above. For these devices, minimizing their power usage to extend operating time between charging cycles is critical. These devices don’t have the energy budget to run a backlit, high-resolution color display. On the other hand, in many cases, it’s more convenient to display a single display on each device that displays simple information (such as battery level or system diagnostic data) without having to log in to the cloud to fetch data using other devices. Server-based bi-stable displays, such as e-paper, which has been a huge success in e-readers such as the Amazon Kindle, are well suited to this application, and there are two main reasons for this. First, the display consumes energy only when it changes (Figure 1). This saves energy that other display technologies use to refresh a static display. Second, e-paper displays are reflective and therefore do not require energy-consuming backlights because their content is visible—at least in reasonable ambient light.

　

　　Figure 1: E-paper is either black or white, depending on the charge of the electrodes.
　　This low-energy technology creates opportunities to add displays to even the simplest IoT devices, so they can present a direct, human-readable interface. If your IoT device can receive data from its cloud as well as send data, this creates the opportunity to, for example, display a payment card showing your current credit balance, or a loyalty card containing a scannable entry code or notification of a special offer.
　　Of course, in situations where an IoT device needs to display rapidly changing data or operate in a dark location, e-paper displays are much less effective. For such applications, TFT LCDs and OLEDs can provide useful alternatives.
　　LCDs have improved dramatically in quality over the past few decades, thanks to their widespread use in flat-screen TVs, mobile phones, and computers. Displays. The resolution of some screens is now so high that it is almost impossible to see individual pixels with the naked eye, while gamers and action movie enthusiasts have pushed display refresh rates to the point where the fastest action can be clearly displayed.
　　This means LCDs are best used in IoT applications that require a rich multimedia experience, or are designed to be used in dimly lit locations where a backlight can provide the necessary screen contrast to ensure legibility. For the same reason, LCDs are less readable in bright light, as this reduces the contrast.
　　However, LCDs are inherently a more energy-hungry display technology than e-paper, and so are best reserved for IoT devices, such as permanently powered thermostats, or for mobile phones whose users are happy to recharge them regularly. The fact that LCDs require a backlight also means that LCD modules will be thicker than e-paper equivalents (Figure 2), while the complex drive electronics for high-information-content displays also present cost and energy-consumption disadvantages.

　　

　　Figure 2: A cross-sectional diagram showing the structure of a typical TFT LCD.
　　A third option for IoT device displays is OLED technology, which is beginning to appear in high-end TVs, mobile phones, and smart watches. OLEDs theoretically have better power efficiency than TFT LCDs because they use electroluminescent materials to emit light when an electric current is applied, rather than using liquid crystal materials as a shutter on the backlight as LCDs do (Figure 3).
　

　　Figure 3: A typical cross-sectional view of an OLED display.
　　OLEDs can control the brightness of individual pixels, enabling displays with pure blacks and very high contrast. They also offer better viewing angles than many LCDs, and can be produced on plastic substrates to create unique shapes, such as the Apple Watch. However, like most technologies, OLEDs have drawbacks, such as aging issues with some electroluminescent materials, sensitivity to water, which often requires expensive encapsulation, and the same issues with sunlight readability as LCDs. In addition, they are still relatively expensive compared to LCDs.
　　The term IoT is so broad it’s almost meaningless. Choosing the right display for your IoT design simply means understanding the requirements of the application, then selecting a technology to match. Smart designers will also make sure they understand how available technologies, such as e-paper, can bring additional, perhaps unexpected functionality to their items, helping them differentiate them from the billions of other devices that make up the IoT.