Getting to the core of rugged transportation systems: Overcoming challenges of both general and application-specific design

Identifying the correct format for each design and combining it with the correct manufacturing approach will reduce long-term customization woes.

1Designing for rugged, small form factor applications presents challenges, but there are form factors and manufacturing techniques that accommodate most requirements for either general or application-specific design. Mobility and environmental extremes are critical considerations for transportation applications; however, by selecting the right core and rugged framework, focusing on and prioritizing any added customization becomes a much simpler mission.

Transportation means movement. Movement means variability. Variability means design challenges. When building a small form factor embedded computer for transportation applications, there are inherent design challenges regardless of application-specific requirements. In fact, it can be argued that small form factor design trends are paradoxical. As form factor size decreases, functionality requirements increase. And at the same time that processing power requirements heighten, lower power consumption and lower thermal output are expected. Now add to that the requirement for ruggedness to accommodate for the shock, vibration, humidity, and temperature extremes and variance inherent in mobile and outdoor applications; developers are often left wondering where they can safely compromise while still meeting overall application design specifications. Knowing the application’s needs and what already exists on the market that fits those requirements makes transportation design less daunting.

Choosing formats

PC/104 and Embedded Board eXpandable (EBX) are good format options for designs that can handle slightly larger Single Board Computer (SBC) form factors. Intended for data acquisition in rugged environments, the PC/104 embedded computing format has no backplane, instead allowing modules to stack together like building blocks – more rugged than typical bus connections in PCs. And with just 46 square inches of surface area (8" x 5.75"), EBX balances size and functionality with a bolt-down SBC format, supporting rugged embedded designs with higher-performance Central Processing Units (CPUs) – such as those using multicore technology for networking, Digital Signal Processing (DSP), and graphics-heavy applications – and generous onboard Input/Output (I/O) functions to support everything from large data exchange to video.

However, the most extendable and customizable application design method accommodates a broad range of custom and off-the-shelf needs by using modularity. Computer-On-Modules (COMs) are complete embedded computers built on a single circuit board for use in small or specialized applications requiring low power consumption or small physical size. Though they are compact (ETX/XTX at 114 mm x 95 mm and COM Express at 125 mm x 95 mm) and highly integrated, COMs can accommodate complex CPUs.

With the COM approach, all generic PC functions are readily available in an off-the-shelf core module. A custom-designed carrier board complements the COM with additional functionality that is required for specific applications. The carrier board provides all the interface connectors for peripherals, such as storage, Ethernet, keyboard/mouse, and display. This modularity allows the designer to upgrade the COM on the carrier board without changing any other board design features, and also allows more customization of peripherals as dictated by a specific application.

COMs allow system developers to focus on their core competencies and the unique functions of their systems. The COM Express form factor offers flexibility in the development and advancement of ultra-rugged embedded applications for a plethora of industries, including transportation. By using the modular processing block, the designer creates a price and value advantage; he/she isn’t locked into a single vendor for board creation and can customize based on pricing and performance requirements. Because it is easily swapped from a carrier board and comes in one of the smallest form factors, COM Express is ideal for long-life embedded applications with a critical development cycle, as well as more progressive applications that require frequent processor upgrades without affecting other application design elements.

Designing for harsh environments in transportation

Transportation solutions are most often housed outdoors or in moving vehicles, where exposure to a variety of climates dictates the need to operate in extended temperatures and to power up in any extreme. The easiest initial step is to select a rugged board or system that is designed for harsh environments from the ground up. To support the extremes of shock, vibration, humidity, and temperature, care is given to component selection, circuit design, Printed Circuit Board (PCB) layout and materials, thermal solutions, enclosure design, and manufacturing process. Robust test methods, including Highly Accelerated Life Testing (HALT), ensure optimal product design phases in order to meet a product’s stringent requirements, such as -40 °C to +85 °C operating temperature range, MIL-STD, shock and vibration, and long-term reliability.

Onboard train systems also deal with high concentrations of sulfur and humidity when going through tunnels. Designers can look for boards with conformal coating to reduce degradation from such exposure. Conformal coating is used in small form factor manufacturing rather than potting, which is a similar process that uses a heavier material and is harder to inspect, test, and repair. Though considered the highest level of environmental protection, potting encapsulates the entire PCB, which adds weight and expands the dimensions of a unit. Even an extra millimeter can be critical in small form factor design, which is why conformal coating – with a single-part material that conforms to the board – is a better option. A variety of conformal coating materials (such as acrylic, polyurethane, epoxy, and silicone) and application methods (such as brushing, spraying, and dipping) are currently used to protect against moisture, dust, chemicals, and temperature extremes that can potentially damage electronics. The correct coating or application method varies depending on established standard operating conditions for an application. With transportation applications, different coatings may be selected based on a primary need for moisture resistance versus abrasion resistance versus temperature stability.

Maintaining performance while mobile

Transportation applications typically need as much functionality as possible in the smallest form factor, meaning the controller may be burdened with extreme loads of information and intricate tasks. Rugged computing solutions also demand more memory space than ever before for both data storage and application performance. Options for storage include rotating Hard Disk Drives (HDDs) for economy or Solid-State Drives (SSDs), which are truly rugged, but also come at a higher price point (cents per GB for HDDs versus dollars per GB for SSDs). SSD microchips that retain data in non-volatile memory chips and an absence of moving parts make them less susceptible to physical shock, altitude, and vibration issues. SSDs have faster access time and lower latency than do HDDs, but SSDs cannot provide the capacity of an HDD; because of the higher cost per GB, SSDs are typically no larger than 120 GB, while HDDs average 500 GB to 1 TB. Higher performing HDDs also require heavier materials than either a standard HDD or the flash memory and circuit board materials of SSDs.

With in-vehicle surveillance applications, vibration control is critical for capturing quality video. Some rugged boards offer a thicker PCB fabrication to add rigidity so the board can withstand higher levels of vibration strain. The thicker PCB offers stability to the overall surface area, protecting electronic components from damage due to vibration. The thicker PCB also offers the ability to use more copper between layers for thermal considerations. Heat is a common unwanted by-product of processing power. In addition to cooling fans and large heat sinks, which may not always be usable for compact, mobile transportation designs, PCBs with adequate amounts of integrated copper facilitate heat conduction away from temperature-sensitive electronic components to prevent performance degradation.

Another challenge with designing in small form factors is that current power supply technology can put limits on size reduction. Rugged designs, specifically, require a robust onboard power controller to support a wide operating temperature range – on average of -20 °C to +70 °C. An onboard power controller is also critical for mobile transportation applications to support multiple data usage requirements, such as collecting video, remotely checking the health of onboard system devices, and sending command controls.

Balancing connections

For an in-vehicle or outdoor video/audio capture application design, the board itself needs high-performance graphics and host interface support for multiple peripherals. In addition to the integration of a video camera, features such as remote monitoring and wireless video download call for some form of connectivity. Both satellite and cellular connectivity require either an antenna or a device with an antenna to connect directly to the system. Ample Ethernet and serial interface ports – with at least one port supporting RS-232/422/485 for Transmit and Receive – are critical to accommodate function-specific peripherals.

Case study: Onboard locomotive video system

A leading global supplier of technology solutions for railroads wanted to develop an onboard locomotive video/audio capture system to aid in accident investigations and provide safety training to crews. In addition to video and audio recording, requirements for the system included remote monitoring and control, real-time health monitoring, and wireless video download. The system also needed to incorporate solid-state media in a sealed, tamper-resistant housing.

Ampro by ADLINK is a line of extreme rugged embedded computers and systems that provides designers of rugged applications with a head start to development. For the onboard locomotive video/audio capture system, designers created a rugged solution around the Intel embedded architecture and EBX SBC form factor. The design accommodated both the functionality and rugged requirements for the train system with dual Ethernet, CRT and flat panel video, multiple serial and USB ports, SATA and IDE interfaces, CompactFlash socket, PCIe Mini Card socket, high-definition audio, and General Purpose Input/Output (GPIO) support.

A critical byproduct of on-site video/audio capture is reduced litigation and settlement costs due to accurate incident reporting. System reliability is critical to users in terms of Return On Investment (ROI), so designers should build using products that provide documented uptime in their specifications and meet the industry standard of EN50155. Because of the cost and complex nature of embedded computing solutions for transportation, qualification can take a very long time, requiring designers to look for products with a long lifecycle. One way to ensure system longevity is to build with products that follow the roadmap of an established architecture.

Optimal designs for transportation

Though designing for rugged small form factor applications presents challenges, there are form factors and manufacturing techniques that accommodate most requirements for either general or application-specific design. Formats such as PC/104, EBX, and COMs have been created specifically to address rugged embedded system needs, while also handling complex CPU technology for applications that require heavy processing power. Modularity also helps designers create customizations while taking into account cost and value requirements. The bottom line for any rugged design, whether for transportation, military, energy, or infrastructure, is to understand all application requirements and how/where existing formats and products can address those needs. By selecting the right core and rugged framework, focusing on and prioritizing any added customization becomes a much simpler mission.

Jeff Munch is CTO of ADLINK Technology and heads all R&D operations in North America and Asia. Jeff has more than 20 years of experience in hardware design, software development, and engineering resource management. Before joining the company, he spent five years at Motorola Computer Group as Director of Engineering. Jeff is Chair of the COM Express R2.1 Subcommittee, Chair of the AdvancedTCA Subcommittee, and Chairman of the PICMG COM Express Plug-and-Play Subcommittee.

ADLINK Technology