SFFs take to the skies

Drones are taking off: Much more than just for recon or warfare missions, much more than about retail giants leveraging consumers to hasten along government agency approvals. Even more than for spying on your neighbor or on Apple’s new spaceship-shaped headquarters. Just visit your neighborhood unmanned system trade show to see how strong this market segment’s thrust is.

Space is once again the new frontier, this time for small form factor processor modules (SFFs). Design teams are working on airborne unmanned aerial vehicles (UAVs) that deliver packages, UAVs that provide a relay network for Internet access, weather balloons that do the same, and inner-space miniature satellites that collect real-time data and images and send them back to earth. “Earth to SFF, do you read me?”

At the current inflection point, all we know is that we cannot know the breadth and depth of industry applications for drones. From a design standpoint, size, weight, and power (SWaP) are important, of course. The altitude UAVs reach takes design challenges to new heights for processor boards. Additionally, while the reduced temperature aloft is beneficial, lower air density makes it harder to remove heat. The reduced atmosphere, in turn, exposes electronics to cosmic radiation that generally doesn’t affect embedded systems that operate on the ground. Fortunately, most drones don’t need to fly that high, but some do.

Payload and processing

The particular industry and application also play a big role in scoping the design task. Data bandwidths are somewhat limited out across the radio interface, so where image capture or high-sample-rate sensors are involved, significant computation or preprocessing must be done. That addition drives up the drone’s power consumption, forcing heavier processor boards and batteries, reducing the actual payload weight by grabbing a larger chunk of the total weight.

In order to run network stacks for cloud connectivity, we move beyond the 8-bit and 16-bit microcontroller space. There, our attention is immediately drawn toward miniature low-power, low-cost ARM chips and boards with wide operating temperature ranges and TrustZone security. MIPI camera interfaces on some boards allow a quick off-the-shelf development methodology.

Taking the high road

While it’s easy to dismiss the x86 processor architecture as having inherently higher power consumption for this space, it’s worth a closer look. The 64-bit dual and quad-core processors with large caches and PCI Express Gen 3 bandwidth tend to come to mind when thinking about x86. However, several new headless systems-on-chip (SoCs) are available that draw only several watts and are available on commercial off-the-shelf (COTS) boards. Some manufacturers went to a great deal of trouble to add in low-speed (low-power) interfaces like I2C bus and UART serial port. Development kits come with Linux drivers and APIs for these interfaces, making it easier to attach sensors, A/D converters, and so on. Developers, equipped with the well-established and reliable x86 Linux operating system, can focus their time on complex algorithms and high-level coding, even building and debugging first on PCs and then moving to the embedded target without having to cross-compile for ARM. Yes, even now x86 still has an edge in the tools and software development ease-of-use department.

Rough, tough, and ready

Flight systems are exposed to harsh environments, including dust, moisture, shock, vibration, and rapid temperature changes (thermal shock/gradient). While land systems have moved away from cables due to reliability concerns, the direct attachment of peripherals to a host board may not address the above environmental characteristics. In fact, smaller boards with locking pin-in-socket/header connectors and short lightweight cables appropriately supported may offer a more reliable system-design path. The flashy performance specs of the rugged high-definition MIPI camera module may draw all the attention, but connecting and mounting it poses mechanical problems. Walk through the list of peripherals and look for small and light modules with cabled versus socketed interfaces, and weigh the tradeoffs. Soldered RAM and eMMC boot flash are more rugged than conventional socket-based counterparts. Now the design task no longer resembles “mission impossible.”

Commercial and ruggedized drones are all the buzz. We are only beginning to imagine the types of sensors, data collection, communication, control, and intelligence that will be placed in locations that humans cannot or should not reach. While many of the camera and GPS-based systems on the market are limited in their application usage, look for a new wave of general-purpose SFF compute boards on the drone horizon.

Small Form Factor Special Interest Group 408-480-7900 info@sff-sig.org