Saving space in cramped ground vehicles is as "simple" as combining computers and displays into one chassis - once the new system challenges that arise are managed.

The modern battlefield depends on computers on the move. While the practice of embedding a range of rugged computers into military vehicles is well-established, the human-machine interface (HMI) for these systems presents new challenges, especially with the need for real-time, high-definition video. A vehicle such as a Stryker personnel carrier, for instance, may contain multiple systems for communications, weapons control, identification friend or foe (IFF), battlefield mapping, inertial navigation, and more, and many of those systems require a display as part of the human-machine interface.

The Stryker appears to have more interior room than a Humvee, mine-resistant ambush protected (MRAP) vehicle, or Apache cockpit to incorporate all those systems, but that space fills up quickly. Moreover, while rugged embedded computers can be tucked into every available nook and cranny, the HMI displays to interact with them must be easily accessible by onboard personnel. Yet what’s the tradeoff between more computer equipment that enhances the vehicle’s battlefield utility and interoperability versus that equipment taking up space at the expense of personnel comfort and amount of crew and gear that can be carried?

Reducing individual chassis size is an option for freeing up space. Another is combining more functions into each box to reduce the total number of vetronics chassis. Taken even further, since the HMI must remain – it can’t be eliminated – why not move a whole vetronics box inside the HMI itself?

A panel-PC-style “smart display” that integrates a vetronics chassis and computer subsystem and display into a single, rugged, application-tailored form factor is an ideal option for these mobile applications. These smart displays can reduce the total space required for separate computer and display, and can be networked so that a single smart display interfaces with multiple systems.

Figure 1: General Micro Systems photo of a typical ground vehicle architecture with commander’s display and mission processor, plus one or more crew displays and associated computers (such as for navigation and IFF).

In Figure 1, the General Micro Systems architecture shows one or more computers feeding purpose-built HMIs. Merely integrating each HMI’s computer into the display chassis itself will free up space in the vehicle, but that move changes a few things: We’ve moved some of the heat load from a separate box into the display, created some new HMI mounting challenges to remove that heat, and possibly wreaked havoc with the cabling.

The upshot is that while an integrated panel PC will free up space, the designer needs to pay attention to these three challenges:

HMI heat dissipation
HMI mounting for cabling and usability
Video or local-area network (LAN) integration between multiple or “slave” displays

Integrated computer and display bring new heat-dissipation challenges

Soldiers commonly refer to computers in vehicles as “personnel heaters.” For missions in snowy areas, that warmth might be appreciated, but recent wars are primarily being fought in deserts; the last thing warfighters need are additional heat sources inside the confined spaces of military vehicles. This reality means that convection cooling is a nonstarter. Fans would simply blow hot air into the vehicle and grit and dust into the computer, making these mechanical elements a source of discomfort for soldiers and a significant point of failure for the embedded computer.

Integrated smart displays, therefore, must use conduction cooling, which can still dump hundreds of watts of heat onto the “cold plate” – the metal shell of the vehicle. That will still eventually heat the interior, so smart displays – which now include a full-featured vetronics computer such as a mission processor – must also use highly efficient design and low-power electronics to keep dissipated heat to a minimum. At the same time, the display must be designed to be as thin as possible to reduce its footprint – there’s no room inside a vehicle for a display that is five inches thick due to a bulky heatsink.

An ideal approach to cooling the whole HMI starts at the hottest point: the CPU and/or video processor. Here, a high-efficiency conduction heat sink can be used that’s composed of a corrugated alloy slug with an extremely low thermal resistance. This acts as a heat spreader at the processor die (see Figure 2). Once the heat is spread over a large area, a liquid silver compound in a sealed chamber transfers the heat from the spreader to the systems’ enclosure. This approach yields a temperature delta of less than 10 °C from the CPU core to the cold plate, compared with more than 25 °C for typical systems. In this manner, the increased heat load of the computer plus HMI is quickly conducted to the vehicle’s cold plate, while keeping the whole HMI extremely thin.

Another advantage of this hot-spot approach is the effect on shock and vibration. Because the CPU die does not make direct contact with the system enclosure, but rather connects via a liquid silver chamber, that acts as a shock absorber that saves the processor from microfractures that can cause failure.

Mounting options require flexible, customizable design

Computer systems inside military vehicles often require creative mounting options to make the best use of limited space for equipment and personnel. While embedded computers can be tucked out of the way, the challenge for displays is mounting them with appropriate viewing capability for operators to manage weapons control, monitor maps, examine video, and more.

Smart displays can be bulkhead-mounted (cut into the vehicle’s wall) or surface-mounted on the wall; can fold down from a ceiling mount; or can be installed on a swing arm. Each of these options requires a different cable output location – out the back, from the top or bottom, or right or left side. A modular design approach to the smart display enables the cable location to be easily adapted to any configuration requirement.

Figure 2: This modular smart display from General Micro Systems offers flexible mounting options and conduction cooling, and allows a single display to support multiple computer systems, or to daisy-chain to other smart displays.

Consumer video interfaces not up to the task

Cables present additional challenges, however. Even though a vehicle is a relatively small area, displays and the systems they are connected to may not be mounted close together. In some applications, an operator may need to share information with another operator’s screen. For instance, if one operator receives thermal imaging or moving map data from an unmanned aerial vehicle (UAV) over the battlefield, the operator may need to share that information with a gunner or tactical platoon leader located on the other side of the vehicle.

Cabling may need to snake as much as 20 feet around the inside of the vehicle perimeter rather than taking the shortest distance. Video quality breaks down over these long distances using typical video interfaces such as HDMI or DisplayPort. Another factor: The electromagnet interference (EMI) from the vehicle’s engine and alternator can also affect performance, which can hamper the safety and efficiency of the soldiers in the vehicle.

One way to deliver video is digitally over a LAN. For some implementations, a single display can provide the interface for multiple computer systems. Packetized video is efficient and can be delivered over long runs using video protocols as long as each HMI includes 1 GbE or 10 GbE [Gigabit Ethernet] network interfaces up to the task.

GigE Vision is a high-performance interface standard designed for industrial cameras that transmits high-speed video and related control data over Ethernet networks. This standard enables video to be routed to multiple displays within a vehicle – or from a camera outside the vehicle to the display – without running additional cables between systems. A setup using an integrated smart display and network server is also possible, which would provide a backbone for digital switching of video data from a central, compact workstation.

Another way to route video between master and slave displays is by daisy-chain method; however, most civilian commercial off-the-shelf (COTS) video standards are not up to the task. Fortunately, the Society of Motion Picture and Television Engineers (SMPTE) has developed high-performance standards for long cable runs. High-definition serial digital interface (HD-SDI) is standardized in SMPTE 292M, which supports uncompressed video streams at full high-definition rates that can run over hundreds of meters with no quality degradation. These cables can also be used to connect cameras outside the vehicle to computers and displays inside, or to daisy-chain computers and displays as needed.

Smart design for smart displays

The human-machine interface is a traditional challenge in demanding, space-constrained environments, but with the right design approach, an integrated rugged display and computer makes mobile battlefield applications viable and reliable.

Chris A. Ciufo, the CTO of General Micro Systems, is a veteran of more than three decades of the embedded systems and semiconductor industries. Ciufo brings extensive experience working with government program offices and prime contractors for M1A2 and M2A3 (Army), F14D (Navy), AAAV (USMC), and B-2 (USAF). Ciufo holds degrees in electrical engineering and materials science from the University of California.

General Micro Systems www.gms4sbc.com