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Embedded Systems, Video Standards and TFT Displays

  Published: 12/03/2019

The use of medium to small size (< 12") TFT displays has become widespread today. Consider a typical journey into any market town or regional city in the UK: point-of-sale systems on petrol station forecourts, ticketing machines at the car park, hand-held self-checkout systems at the supermarket, appointment booking systems at health centres, spare parts information terminals at auto retailers - the use of display technology is now ubiquitous. Additionally, there are many other applications where display technology prevails: process control, security, manufacturing, audio-visual, in-vehicle to name but a few.
To the uninitiated it's 'just a display' but there's obviously more to it than that. Most of these applications and systems are embedded systems - an embedded system is a combination of hardware and software that is designed to perform a specific real-time process or function and is embedded within a larger electrical or mechanical system. Many embedded systems will employ some form of user interface - predominantly a graphical display with associated input keys or touch screen to enable user inputs and responses.
Designers creating tomorrow's embedded systems will benefit from tools and development systems to simplify the design process. The display and user interface can, on occasion, become a belated afterthought with the embedded hardware and software taking priority. To ensure that an exceptional end-user experience is created an appreciation of video standards, embedded computing and TFT displays is deemed essential.

Video standards
Video Graphics Adapter (VGA) is well known as the analogue standard of connection for video devices such as monitors and projectors. The commonly used acronym VGA generally refers to the types of cables, ports and connectors used to connect monitors to video cards. VGA cables have 15-pin connectors which carry Red, Green and Blue (RGB) analogue video signals, horizontal and vertical syncs, ground signals and monitor IDs. Though VGA is still in use today, it has largely been superseded by digital video interfaces HDMI and DVI.
What is HDMI and why is it so useful?
High-Definition Multimedia Interface (HDMI) is a digital video interface for transmitting uncompressed video data and digital audio data from an HDMI-compliant source device, such as a display controller or single board computer, to a compatible monitor, projector or HDMI-enabled display. In late 2003, HDMI came to prominence in consumer products, as the video/audio data interface used on high definition TVs, monitors and audio visual equipment featuring HD (720p) and Full HD (1080p) displays.
Several versions of HDMI (1.0 through to 1.4) have been developed and deployed since initial release of the standard. The most recent versions 2.0 and 2.1 now support for higher resolutions and higher refresh rates, including 4K and 8K at 120 Hz. The maximum pixel clock rate for HDMI version 1.0 is 165 MHz, which is sufficient to allow 1080p and WUXGA (1920 × 1200 pixels) at 60 Hz. Typically, however, for embedded applications, version 1.0 to 1.4  are suitable for use.

HDMI transmits high-speed serial data using Transition-minimized differential signals (TMDS), which is similar to Low-voltage differential signals (LVDS). Data is transferred using twisted pairs which reduces electro-magnetic interference (EMI) and enables faster data transfers with increased accuracy. Three TMDS twisted pairs are used to transfer Red, Green and Blue (RGB) video data.

There are five different types of HDMI connector. The 19-pin Type A HDMI connector is the most widely used and is found on PCs and AV equipment, and single board computers. The four other HDMI connectors include Type B which can be used for dual link operation, Type C connectors have a mini format, Type D is a micro format and Type E is used for automotive applications.

HDMI has become an established standard and is being continually enhanced to further improve performance and integration with additional features such as Ethernet data connection. As HDMI continues to be regularly updated, the standard is likely to remain the de-facto digital video interface of choice for many years to come.

Embedded Computing
Single board computers (SBC) have become increasingly popular with the advent of low-cost high-performance processors, increased levels of peripheral integration and ease of access to general purpose I/O. The proliferation of SBCs such as the Raspberry Pi, BeagleBone, LattePanda, DragonBoard, HummingBoard, Tinker Board - to name but a few, has enabled many of them to be used as embedded system controllers.
The pioneer and forerunner of many of these low-cost SBCs was the Raspberry Pi. Initially introduced in 2012, it has since sold in excess of 14 million units and has found widespread use in education establishments, hobby electronics and with many professional electronic designers. Designed and integrated into many varied applications the Raspberry Pi has since developed a significant reputation and a widespread user community.

HDMI TFTs and the Raspberry Pi
Using the Raspberry Pi SBC, design engineers from innovative UK display distributor, Midas Displays have  conceived a new range of integrated HDMI TFT display modules. Using three different sizes of TFT display,  5.0" (800 x 480 pixels), 7.0" (1024 x 600 pixels) and 10.1" (1280 x 800 pixels) a simple, and easy to use display terminal with a direct HDMI input has been developed.
The three featured TFT displays have high brightness and high contrast specifications that will produce a bright, colourful display with excellent image clarity. Resistive and Capacitive touchscreens are also offered, which can also been employed to create easy-to-use graphical user interfaces.
A Type A HDMI cable can be connected from an HDMI source, computer or SBC directly into the TFT display module. This provides an easy-to-use display platform ideal for the development and prototyping of embedded control systems and applications.


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