Application-Specific Display Solutions
Display devices enhance the embedded system’s capabilities with graphical representation. Power consumption rate, performance-cost ratio, and display screen size are important factors for display selections.
Embedded systems are for the most part designed with display devices as system requirements. You can choose from a wide variety of displays, and can even design a display, to fit your embedded system. The custom-built screens often deliver users a more integrated and satisfying experience without unnecessary additional features.
BRIEF INTRODUCTION TO DISPLAYS
The earliest widely used electronic display was the cathode ray tube (CRT), first demonstrated by Karl F. Braun in experiments he conducted in 1897. The cathode-ray oscillograph became commercially available in 1922. These monochrome CRT displays were initially used primarily for oscilloscopes, but eventually became common in black-and-white televisions. Commercial color CRT displays were first produced in 1954 and rapidly became more prevalent. CRT displays were the most popular display technology for television and computer monitors for more than half a century, until they were gradually replaced by Liquid Crystal Displays (LCDs) beginning in the 2000s.
Widely used LCDs include light-emitting diode (LED) backlit LCDs, thin-film transistor (TFT) LCDs, and Quantum dot (QLED) displays.
For the last few years, LED displays have been widely used for almost every area of application. The first LED device, HP Model 5082-7000 Numeric Indicator (Figure 1), was introduced in 1969. A wide range of LEDs and LED displays are commonly used for embedded systems, including organic LEDs (OLEDs), active-matrix organic LEDs (AMOLEDs), and Super AMOLED displays. Other types of displays include segment displays, vacuum fluorescent displays, electroluminescent displays, plasma displays, and projector displays.
These technologies are rapidly evolving from high-voltage CRT displays to the latest cutting-edge, paper-light touchscreen displays. As the reader is no doubt aware, over the past few decades display devices have become almost ubiquitous.
DISPLAY SOLUTIONS FOR EMBEDDED SYSTEMS
The display requirements for an embedded system might include simple segmented displays, alphanumeric displays, or graphics displays. Simple segmented displays are useful when your system only needs to display numbers or a small set of letters. In embedded systems, MCUs are integrated with segmented displays to display numbers, characters, and icons. Seven-segment displays are common. Some segmented displays are available with more than seven segments so as to enable users to display a wide range of patterns.
Alphanumeric displays can be segmented displays or dot-matrix displays, and are used to show alphanumeric data or functional parameters of an embedded system. The display provides single or multiple rows of character cells that consist of fixed-size arrays of pixels and can display a wide variety of characters and symbols. There can be several combinations of character cells per row.
Nowadays most embedded systems use graphics displays that consist of large, individually addressable sets of pixels. These displays are capable of displaying everything from simple text to images to full-motion video. The cost of graphics displays is higher than simple segmented and alphanumeric displays, but of course many of these products offer advantages over simpler display options. Graphics displays can be integrated with many of the latest technology solutions in order to deliver a higher quality graphical representation.
SEGMENTED DISPLAY SOLUTIONS
Segmented displays require a low level of power and thus help extend battery life and reduce system costs. There are different sizes, types, and ranges of segmented displays, and these are available with seven segments, 16 segments, or other options. The display systems are simple, scalable, and usable for a wide variety of applications. Segmented displays are typically LCDs or LEDs.
Seven-Segment Display: A simple seven-segment display is programmable and can individually turn on or off each of its segments, which can be used to display the numbers 0 to 9 and letters such as A, C, E, F, H, h, L, P, R, T, and U. Würth Elektronik’s new WL-S7DS seven-segments display SMT single digit (Figure 2) is designed with industrial-standard size and schematics, and has a low power consumption. It has a grey surface with milky, diffused segments.
WL-S7DS works with forward-DC and is suitable for high peak current up to 100mA. The SMT single digit is available in four different sizes—5mm, 7.62mm, 10mm, and 14.22mm. The 5mm WL-S7DS power dissipation, peak forward current, continuous forward current, and reverse voltage are 68mW, 100mA, 20mA, and 5V respectively. The wavelength, optical intensity, and forward voltage tolerance under measurement conditions are ±2nm, ±15%, and ± 0.2V respectively.
The operating temperature range is -35 to +85°C. Its storage conditions in original packaging are more than 40°C with up to 90% relative humidity. The WL-S7DS can be used in applications such as audio equipment, instrument panels, and digital read-out displays.
16-Segment Display: The 16-segment display is programmable and can individually turn on or off each of its 16 segments to produce a graphic pattern. The character generator is often used to translate a seven-bit ASCII character code to 16 bits by controlling which of the 16 segments is turned on or off.
Kingbright’s PSA08-11EWA (Figure 3) is a 20.32mm 16-Segment single-digit alphanumeric display with a low-current operation and high-contrast light output. The single-digit display comes with a gray face with white segments and is easily mounted on PC boards or sockets. The PSA08-11EWA power dissipation, peak forward current, DC forward current, and reverse voltage are 75mW, 160mA, 30mA, and 5V respectively. The operating and storage temperature ranges from -40°C to +85°C. Its junction temperature and electrostatic discharge threshold are 125°C and 8000V. PSA08-11EWA is a high-efficiency red source color display device that is made with gallium arsenide phosphide on a gallium phosphide orange LED. It can be used in a variety of devices, including home and smart appliances, as well as industrial technology.
There are other variants such as the 14-segment and 22-segment displays. The 14-segment display does not split the top or bottom horizontal segments. The 22-segment display allows for a greater ranger of segment management, and can even create lower-case characters with descenders.
ALPHANUMERIC DISPLAY SOLUTIONS
Alphanumeric displays have some extended functionality over simple segmented displays. The displays are commonly used for energy meters, AC remotes, test and measurement equipment, handheld devices, process control equipment, and data loggers. They can show one or several lines of data and are most commonly available with reflective LCDs and LEDs.
There are many different options for alphanumeric displays, and manufacturers offer quality products around the globe. For the embedded system where energy efficiency is a particular concern, it is best to avoid LCD backlit alphanumeric displays.
Winstar’s WH1602L1 character dot matrix LCD module (Figure 4) is a 16×2 character LCD with 5×8 dots including the cursor. The display module’s ideal power supply is +5V (negative voltage optional) and is also available for +3V. The LCD module is built-in with an ST7066 controller IC and has a 6800 4/8-bit parallel default interface. Using an RW1063 controller IC, it is also available in SPI and I2C interface. The WH1602L1 module is available with several different backlight colors, such as green, yellow-green, blue, amber, red, white, and white LED.
The LEDs can be driven by PIN1, PIN2, PIN15, PIN16, or A, and K. The display module operating temperature range is -20°C to +70°C, and the storage temperature range is -30°C to +80°C. Winstar offers several interface options for their WH1602L1 series including WH1602L1 (6800 interface with ST7066 IC) WH1602L2 (SPI interface with RW1063 IC), and WH1602L3 (I2C interface with RW1063 IC).
GRAPHICS DISPLAY SOLUTIONS
Graphics displays are widely used for a broad range of applications, today. They consist of individually addressable pixels and are capable of displaying anything.
Graphics displays can be used in embedded systems, from tiny display screens, to large wall display screens, to very large scoreboard screens. Commonly used graphics displays may include E-ink displays, LED displays, and OLED displays.
Touch Screen HDMI: Many embedded systems need touchscreen displays, especially with input and output capability. The touchscreen displays with a high-definition multimedia interface (HDMI) are commonly used for IoT, AI, and robotics applications. Touchscreen HDMI displays can simplify your projects and sometimes help to reduce I/O components.
Waveshare touchscreen displays are designed as embedded display solutions. Capacitive touchscreen LCD (B) displays come with HDMI, have a low-power consumption, and are good for resistive and capacitive operation. The display size can vary from 3.5” to 10” and is usable for Raspberry Pi and other systems. The Waveshare SKU 10829 (Figure 5) 7” capacitive touchscreen LCD (B), 800×480 pixels, has a great price point for what it offers. The touch control supports up to five-points touch, backlight control, and energy efficiency. The display can be used normally with an external 5V/2A power supply through the DC interface.
RGB LED Matrix: Many systems need large-size displays, such as video walls, digital signage, and scoreboards. The display screen can be a few meters to hundreds of meters long, and deploying simple graphical displays will be difficult and costly. An RGB LED matrix display is an ideal solution for those issues. There are several types of RGB LED matrix displays, and these panels can be daisy-chained together to be formed as even bigger LED displays.
Sparkfun’s COM-14824 RGB LED Matrix Panel 64×64 (Figure 6) uses 4,096 LEDs on a 7.5”×7.5” board. The RGB LED matrix panel supports a 1/16 scan rate to create animations, videos, games, or other fun displays. An IDC connector and a seamless frame enable the panels to be daisy-chained together to form bigger LED displays. Sparkfun’s RGB LED matrix panels require a regulated 5V supply for power. The panel operating and storage temperatures are -20°C to +50°C and -35°C to +85°C, respectively.
The RGB LED matrix panel is good for large embedded display solutions and easy to use. Its best viewing distance is 3m to 20m and the best viewing angles are horizontally up to 160° and vertically up to 120°. To work with standard Arduino, the display will require an extra pin for multiplexing compared to the other LED Matrices.
The recent evolutions in modern display technology create new opportunities for embedded display solutions. The latest paper-thin LED flex panels, for example, promise exciting advancements in embedded systems and even wearable tech components. There is now a large variety of choices in displays, particularly if you choose to focus on the performance-to-cost ratio, power consumption rate, and display screen size. The right display helps embedded system developers to achieve their goals by enhancing functionalities, and it is important to understand what type of capabilities are necessary for your system and how much you want to pay for them.
PUBLISHED IN CIRCUIT CELLAR MAGAZINE • SEPTEMBER 2022 #386 – Get a PDF of the issueSponsor this Article
Al Mahmud Al Mamun Former (March 2022-July 2022) Editor-in-Chief — Editor-in-Chief Circuit Cellar magazine. With a background in engineering, research, and publishing and a master’s degree in Computer Science and Engineering. His passions include Robotics, Artificial Intelligence, and Smart technologies.