RTC Magazine

OEMs who build the tiniest, lowest-power devices tend to use RISC processors and microcontrollers at the heart of their systems. While the x86 architecture can reduce development costs and risk due to familiar programming, performance and off-the-shelf boards ecosystem, the size and power consumption usually squash any such considerations. A solution is needed for those who want the best of both worlds.

While legacy EBX and PC/104 form factor SBCs continue their acceptance in truly rugged applications, there is a new sheriff in town: ISM. An acronym for Industry Standard Module, this new form factor from the Small Form Factor SIG is allowed to be legacy-free and expansion-agnostic. This opens up brand new markets for embedded x86 designs that are not saddled with the added cost, power and board space of parallel bus bridges and old-generation PC peripherals such as PS/2 keyboard and mouse and printer ports.

PoE Reduces Cabling

Previously beyond the reach of high-power x86 processors and chipsets, Power-over-Ethernet (PoE) has gained traction in VoIP phones, wireless access points, LAN switches and factory automation applications where costs and convenience are improved without separate power wiring and wall power transformers. Innovative ultra-low-power processors like Intel’s Atom, combined with the 3.6 x 3.8” ISM form factor, now make it possible for PoE to enter the broad space of embedded computing. Possibilities are endless in this new frontier.

Known formally as IEEE 802.3 or 802.3af, PoE can supply up to 15.4 watts of power to remote devices, although devices must be designed with the assumption that only 12.95 watts are available due to cable losses. With a communications heritage, typically 48V DC is supplied at 350 mA. Some early Atom offerings are targeting 802.3at, dubbed “PoE Plus,” to extend the power available to 25W allowing for remote peripherals, storage devices, LCDs and backlights to be powered as well. But advances in backlight technology, coupled with a renaissance of standardized low-power x86 single-board controllers, are paving the way to the ideal solution for 12.95W PoE applications.

Industry Standard Module (ISM) is a pure 3.6 x 3.8” (90 x 96 mm) form factor that addresses shortcomings of existing small form factors by:

• Fitting x86 circuitry well within the board outline

• Freeing designers from restrictive top- and bottom-side component height zones

• Decoupling expansion interfaces from form factor definitions

• Re-capturing the space wasted by large legacy parallel bus connectors

• Enabling flexible I/O connectorization

• Allowing bus combinations that were previously undefined and unnamed

SBC manufacturers have struggled to fit modern legacy-free platforms onto small form factors without protruding beyond the allowed board outlines with “wings.” Now that the ISA bus, serial ports and even the PCI bus are no longer integrated into low-power chipsets, it takes extra circuitry to meet the needs of many embedded applications. Applications like PoE generally don’t need legacy buses.

The ISM Specification defines the board size, four fixed mounting holes, component height limits and flexible “expansion zones” for I/O and/or bus connectors. The fixed corner mounting holes allow reuse of enclosures without modifications in the future. ISM allows many combinations of bus and I/O connectors as long as those interfaces reside within the defined “expansion zones.” ISM also offers a choice of using right-angle connectors that overhang the board edges, or extending the circuit board if vertical / non-overhang connectors are used.

Legacy-Free ISM CPU

Figure 1 shows the Ampro by Adlink CoreModule 730. Offering a choice of Atom Z510 processor at 1.1 GHz or Atom Z530 processor at 1.6 GHz, the CoreModule 730 provides the basics of an embedded controller in a small ISM size without the overkill of larger motherboards like Mini-ITX. The single-chip Intel US15W chipset provides modest expansion buses and I/O sufficient for controller applications. The board’s feature set includes a Gigabit Ethernet port, several USB ports, eight GPIO pins and a CompactFlash socket on the bottom of the board. Since space is at a premium, pin headers are used for flexible cabling.

Only the I/O used by an application is cabled out to the enclosure, and in the locations where desired. SBCs with fixed I/O blocks are convenient but inflexible. Computer-on-Module architectures require custom carrier boards to be designed in order to bring out the I/O, consuming development budgets and extending project risk and schedule.

Solid-state drives (SSDs) are gaining in popularity for mass storage. They offer small size, low power, lower MTBF and no spin-up time compared to rotating disk drives. Windows XP Embedded brings the familiar desktop user interface in a modular footprint (image size)—even down to 1 Gbyte and below. For many applications, a 1 Gbyte CompactFlash device is very mainstream and cost-effective, well below the steep part of the flash price curve.

A short copper plate with fins spreads the modest heat from the Atom processor and single-chip US15W chipset over the full breadth of the board. The SODIMM RAM memory is also cooled by this heatsink. The thermal solution has a low thermal resistance with minimal airflow inside the system enclosure, allowing operation to +70°C air temperature just above the heatsink. The heatsink can be attached to the outer enclosure in places, further removing heat from the tiny SBC (Figure 2).

At the front of Figure 2 are pin headers for two USB ports and one Gigabit LAN port, as well as an IDE connector that can be used in other applications. These connectors are not covered by the copper heatsink so they are easily cabled to the outside of the enclosure.

PoE System Solution

The Jaco Electronics JDS104CA01 (Figure 3) is a new x86-based PoE solution with full LCD and touch screen capability. Designed as a wall-mounted user interface to a professional audio control system, the unit includes: 10.4” SVGA LCD, resistive touch screen and 1.6 GHz Atom CPU powered Ampro by an Adlink CoreModule 730. This panel PC system uses only 11 watts, landing safely under the IEEE 802.3 PoE power requirements. The combination of x86 and ultra-low power is the best of both worlds that many have been waiting for. JDS104CA01’s configuration creates a reference design that is suitable for application in industrial, medical and other arenas using LCD sizes up to 12.1” diagonal.

Many of today’s panel PCs strive for a fanless, low-powered, high-performance product. While these panel PCs may be low powered compared to some standards, they do not come close to meeting the 12.95 watt PoE requirement. Table 1 compares a typical low-powered panel PC to JDS104CA01.

A low-powered SBC is only the first step to designing a high-performance system that is PoE-compliant. As one can see from Table 1, an LED backlit LCD also plays a major role in power savings.

The emergence of LEDs in LCD backlighting has allowed for numerous advantages for today’s applications. New high-efficiency LEDs have allowed displays to use less power for the same luminance. For example, an AUO G104SN02 V2 10.4” display with 400 nits of luminance uses 5.2 watts of total power. This is 32% less power as compared to similar displays utilizing CCFL backlights.

The power savings due to LED backlights does not stop there; LED backlit panels require even less power due to the differences in drive requirements compared to their CCFL rivals. The change from a DC-AC inverter to an LED driver with a constant current circuit allows for a simpler, more efficient solution that does not inherit the EMI problems that accompany CCFL inverters. In fact, many of the latest LED backlit LCDs embed these constant current circuits; this eliminates one more part in the design and simplifies the total solution. The AUO G104SN02 V2 is one example of an LCD with a built-in LED driver circuit. This driver circuit is included in the 5.2W of total power from the LCD and allows the system to eliminate an additional 1.2W that is lost by the inefficiencies of the CCFL inverter. If you add up the total power savings in a solution with LED backlights, you can save your system about 2.5 watts.

A PoE power conversion board is the next essential part of this system design. The power conversion board connects a power-injected Ethernet cable and separates the power and communication signals. The board converts the 48 volt input to the 5V and 12V levels that the SBC and LCD need for operation. The PoE power board is designed to receive an input of up to 12.95W and supply an output of up to 11.00W.  The CAT5 cable entering the unit is the only external cable needed to run the system, making for a clean and elegant solution. The PoE board used in the 10.4” design is 85% efficient and has a PC/104 mounting scheme that can stack on top of the ISM Atom board.

Although all low-power components are selected, heat dissipation is still an important design consideration in such an application. Many PoE applications require fanless solutions in sealed enclosures that do not allow for airflow through the unit. Heat sinking and proper enclosure design become critical to the long-term reliability of the product. The Atom-based SBC is designed to use the outside enclosure to help dissipate the heat generated from the SBC. The low-power and customizable solution also allows for the system to be designed to withstand harsh environments or meet many unique enclosure requirements.

Although not essential, touch screens often complement many of the current PoE applications in today’s market. Whether it is resistive, capacitive, projected capacitive or any other touch screen technology, touch screens provide a convenient user interface to operate interactive applications. The touch screen also allows for a sleek look by having no buttons on the faceplate, one single in/out wire and no mouse or keyboard.

Jaco Electronics

(877) 373-5226.

Hauppauge, NY.

[www.jacodisplays.com].

ADLINK Technology

San Jose, CA.

(408) 360-0200.

[www.adlinktech.com].