Screens for All Seasons
Displays designed for use in embedded systems keep evolving. Today’s crop of display products feature tiny form factors, sunlight-readable capabilities and embedded-friendly interfacing.
We’ve come a long way from the days when adding a display to an embedded system meant taking a laptop or consumer device LCD and just putting a protective covering on it. Today’s displays for embedded systems continue to offer new formats and smaller sizes. New levels of ruggedness are opening the door to harsh environment applications. And integration and interfacing continue to become easier and less costly.
Over the last 12 months, embedded display vendors have launched a variety of new display solutions. These products span a diverse set of screen technologies and formats including, TFT LCDs, IPS LCDs, OLEDs, e-paper displays, panel PCs and more.
DIRECT SUNLIGHT CAPABLE
Displays designed for outdoor use need to meet a variety of requirements that don’t apply to office desktop displays. Along those lines, in January Newhaven Display announced that its 5″ TFT LCDs are now available with sunlight readable screen technology. The sunlight readable TFT LCD modules feature 3M enhancement film and LED backlights rated up to 1,000cd/m2 to deliver brightness levels suitable for any environment, including direct sunlight.
The new 5″ sunlight readable TFTs are also available with added capacitive touch panel capability (Figure 1). Under the brand name “Sunlight Readable TFT LCD Modules,” the 800×480-pixel units run off 3V and have a 24-bit parallel interface. MVA (70 degree) viewing angles are supported along with wide temperature support: -20°C to 70°C.
According to Newhaven, the company’s engineers can modify your display’s interface with HDMI, SPI or other interface types. You can adjust the length, size, pinout and shape of the display’s cables. You can choose capacitive or resistive touchscreen technology. Newhaven can adjust the glass thickness or shape of the touch panel to fit your embedded design.
OLED SOLUTIONS
Organic light-emitting diode (OLED) display technology has been growing in popularity in embedded applications. OLED displays make use of organic compounds with self-emissive characteristics. According to display vendor Noritake, OLED displays produce higher contrast images, have a wider viewing angle, faster response and are thinner and more lightweight compared to conventional displays.
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An example of Noritake’s OLED offerings is its GE256X64C-7933B OLED display module (Figure 2). This OLED module works as a character display by simply sending ASCII code to the module. The on-board flash memory can store up to 256 screen images, which significantly reduces software development costs and host controller memory usage. In addition, Noritake provides free design resources including command evaluation software, code libraries and downloadable datasheets. The module’s size and GU7000 derived command set makes it easy to replace old LCD/VFD/OLED displays, says the company.
The display module features simple command-based operation. Noritake’s firmware eliminates long start-up (initialization) times and reduces character display data overhead when performing a simple command operation like displaying a letter “A”. Only a single ASCII character code (0x41) is needed. Additionally, backspace (0x08), horizontal tab (0x09), line feed (0x0A), home position (0x0B), carriage return (0x0D) and display clear (0x0C) work exactly like a terminal display. Display controls, font options, image controls and screensaver functions are also available. The GE256X64C uses the same command set as Noritake’s GU7000 series display modules.
Interfacing to microcontrollers (MCUs) is easy with the GE256X64C. The module is available with industrial standard serial interfaces (UART/I2C/SPI) to directly connect the display module to an MCU. It’s powered by a 3.3V single power supply. The module features a reliable COG (chip on glass) OLED panel construction. It boasts long life specs of 70K hours until 50 percent brightness attenuation.
ULTRA-SMALL LCD
A growing number of embedded applications require extra-small displays. In the past, such solutions were expensive because of the complex miniaturization of components. Bucking that trend, 4D Systems offers a 1.3″ embedded graphics display that is designed with a low total cost of ownership in mind. The pixxiLCD-13 is a 1.3″ round color TFT-LCD compact intelligent display module that offers an array of functionality and options for any designer, integrator or user wishing to add a full color HMI into an application (Figure 3).
Based on in-plane switching (IPS) LCD technology, the round IPS display offers wide viewing angles. The pixxiLCD-13 is powered by the configurable PIXXI-28 graphics processor, allowing various functionalities such as touch detection, microSD or serial flash memory storage, GPIO and ADC, along with multiple millisecond resolution timers, and UART and I2C communication.
The pixxiLCD-13 embedded graphics display comes in two variants: a non-touch pixxiLCD-13P2 and a capacitive-touch pixxiLCD-13P2-CTP-CLB. The pixxiLCD embedded graphics displays are 100% compatible with the 4D Systems’ Workshop4 IDE, which provides users with a wealth of options for programming and controlling their systems. The pixxiLCD displays feature a standard 15-way, 0.5mm pitch ZIF socket interface that carries the UART, I/O, I2C, power and reset signals to/from the display.
According the company, the pixxiLCD-13 is suited for a wide variety of applications, including general purpose low-cost embedded graphics, elevator control systems, electronic gauges and meters, instrumentation, industrial control/robotics, automotive displays, GPS/Sat-Nav systems, medical instruments, heart rate and blood pressure monitors, smart home automation display panels, consumer appliance devices, security and access control panels and vending machine panels.
RPi E-PAPER BONNET
The industry has become familiar with the term “HAT” in the context of Raspberry Pi SBC-compatible add-ons. HAT stands for “hardware attached on top,” a hardware specification for add-on modules for the Raspberry Pi model 3B+ SBC. A whole other set of modules are in the smaller pHAT (for partial HAT) format, although pHATs have no formal definition and don’t have strict specs. For its part, Adafruit has been using the term “bonnets” instead of pHAT for its line of Raspberry Pi add-on modules. On the display side, Adafruit now offers an e-paper display solution for Raspberry Pi in a bonnet format.
The Adafruit 2.13″ Monochrome E-Ink Bonnet for Raspberry Pi snaps onto any modern Raspberry Pi and provides a Python-programmable display with two buttons that can be used to select programs or scroll through options (Figure 4). This bonnet is designed to make it easy to add a 2.13″ 250×122 crisp monochromic e-paper display to your system. E-paper displays are static, meaning that the image stays on the display even when power is completely disconnected. The image is also high contrast and very daylight readable.
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Adafruit offers two starter guides to use with this bonnet, an Open Weather display and an event calendar that auto-syncs with a Google Calendar to show you what your next meeting or event is. Adafruit also provides examples in its E-Ink Python library for developers to use to craft their own projects.
The bonnet comes completely pre-assembled and tested so you don’t need to do anything but plug it in and install the Python code. The bonnet works with any Raspberry Pi computer that has a 2×20 connector, such as the Pi B+, Pi 2, Pi 3, Pi 4 and Pi Zero (and any others that have a 2×20 connector.) On the bottom of the bonnet is a Qwiic/STEMMA QT connector for I2C sensors and devices so developers can plug and play any of Adafruit’s STEMMA QT devices.
PARTIAL UPDATE FEATURE
For its part, Pervasive Displays specializes in e-paper displays (EPDs). In May, the company announced that it has integrated a next-generation partial update feature into its EPDs (Figure 5). The driving waveforms used for these partial updates have been optimized to deliver superior image quality, outperforming what other EPD vendors are able to achieve, says the company.
According to Pervasive Displays, in most EPD application scenarios, like electronic retail shelf labeling, a conventional global update is sufficient. In those displays, every pixel on the EPD is refreshed because there are no time pressures and this can be done when the EPD is not being viewed by anyone (such as when the store is closed). There are, however, certain applications that require rendered information to be refreshed at a quicker rate, while still being viewed. That, says the company, is where a partial update capability has major appeal.
Using partial updates, rather than refreshing every pixel, the rendered information in a smaller section of the EPD can be refreshed. Changes can be implemented within a shorter time frame and there is even potential for simple animations to be displayed. Until now, the drawback of this has been that partial updates can often result in ghosting, where traces of the previous image remain present on the new image. This impacts on image quality and detracts from the user experience. It may also reduce the EPD’s working lifespan.
Using Pervasive Displays’ advanced driving technology, the waveforms generated for partial updates are much more effective. Partial updates can take as little as 0.5 seconds to complete which is around a quarter of the time needed for a global update. However, ghosting issues are avoided and the EPD’s long-term operation is maintained. As with any display technology, the faster e-paper can be updated, the better. Developers can use fast and partial update modes in place of a global update to improve the user experience when a display is updated “live” in front of the user. Table 1 compares the three kinds of EPD updates. Both fast and partial update modes enhance flexibility for developers to choose a method best suited to their application.
| Update Type | Global Update | Fast Update | Partial Update |
| Initialization | Panel initialization | Panel initialization | Panel initialization |
| Image data upload | Full screen image New image buffer with all 0x00 buffer |
Full screen image Previous image buffer and new image buffer |
Partial window image Previous image buffer and new image buffer |
| Panel update | Whole screen Flashing effect |
Whole screen Fast mode |
Partial window Fast mode |
| Image quality | Optimal quality | Possible ghosting | Possible ghosting |
| Upload image speed | Slow | Slow | Fast |
| Update image speed | Slow | Fast | Fast |
| Overall speed | Slow | Faster | Fastest |
SUNLIGHT READABLE PANEL PC
A key category of display solutions in the embedded space is panel PCs. Panel PCs are display systems that are meant to be mounted on a factory wall or on the side of an industrial machine. They also are found in transportation systems like user interfaces on-board trains or buses. Rather than simply being a display, panel PCs embed a complete SBC, providing a complete embedded solution. Circuit Cellar’s 2020 overview of representative panel PC products is available at [1].
In an example of such technology, in April Cincoze launched its CRYSTAL line of industrial panel PCs with sunlight-readable displays in various sizes and with a modular design (Figure 6). The sunlight-readable display models feature crystal clear displays for bright daylight viewing and are strong enough to withstand the rigors of the outdoors. They are suited to outdoor kiosk use in smart cities, such as smart bus kiosks, automatic ticket vending machines, vending machines, express cabinets, public information stations and smart mailboxes.
The Cincoze sunlight-readable panel PC series uses Cincoze’s patented Convertible Display System (CDS) modular design to combine an industrial touch display and an industrial embedded computer module to create an easy-maintenance, easy-upgrade and future-proof panel PC. The embedded system component offers various options including, Intel Atom, Pentium and Core i3/i5 processors, up to 64GB of memory and two 2.5″ HDDs/SSDs, selectable to match with system performance needs. For the display, there are options from 8″ to 21.5″ with projective capacitive (PCAP) touch displays, and high-brightness 1600 nits backlight that make them clearly visible even under outdoor sunlight.
Specific I/O requirements for outdoor kiosks vary between applications and between installation environments. The Cincoze range of sunlight-readable panel PCs have the most commonly needed I/O connections right out the box, including USB 3.0, COM and GbE LAN, to connect to devices like barcode readers, cameras and card readers. For specialized applications, there is an M.2 E key and two full-size mini-PCIe slots for wireless connectivity modules or any of Cincoze’s exclusive mini-PCIe expansion card (MEC) modules for additional COM, USB and LAN ports. To ensure uninterrupted operation, the sunlight-readable panel PCs can withstand a temperature range of -20°C to 70°C, and the front panel is waterproof and dustproof with an IP65 rating. The super-hard 7H touch surface is scratch-resistant and tough enough to withstand heavy impacts. 
For detailed article references and additional resources go to:
www.circuitcellar.com/article-materials
Reference [1] as marked in the article can be found there.
RESOURCES
Reference:
[1] Circuit Cellar 363, Datasheet: Panel PCs
4D Systems | www.4dsystems.com.au
Adafruit | www.adafruit.com
Cincoze | www.cincoze.com
Newhaven Display | www.newhavendisplay.com
Noritake | www.noritake-elec.com
Pervasive Displays | www.pervasivedisplays.com
PUBLISHED IN CIRCUIT CELLAR MAGAZINE • JULY 2021 #372 – Get a PDF of the issue
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Jeff served as Editor-in-Chief for both LinuxGizmos.com and its sister publication, Circuit Cellar magazine 6/2017—3/2022. In nearly three decades of covering the embedded electronics and computing industry, Jeff has also held senior editorial positions at EE Times, Computer Design, Electronic Design, Embedded Systems Development, and COTS Journal. His knowledge spans a broad range of electronics and computing topics, including CPUs, MCUs, memory, storage, graphics, power supplies, software development, and real-time OSes.
