Originally appeared in MEDS magazine
Advances in x86 processors, combined with a right-sized Pico-I/O peripheral card ecosystem based upon USB, make it feasible to meet the major requirements of portable patient monitors with fully off-the-shelf building blocks.
Portable medical devices have used custom CPUs and custom I/O blocks for years. From the analog front end to the microcontroller or RISC processor back end, the only way to meet cost, size and feature requirements was with full custom hardware and software. But now, stretched engineering resources, consideration of core competencies, time-to-market pressures, and ubiquitous wired and wireless network connectivity expectations are forcing OEMs to reconsider development methodologies and processor architectures.
Fortunately, a new series of tiny PicoI/O modules (Figure 1) is poised to allow next-generation patient monitors to take on all the desirable graphics and connectivity characteristics of notebook or tablet computers, using a standardized bus interface to integrate with small, long lifecycle embedded x86 single board computers. Pico-I/O modules stacked on top of tiny x86 SBCs can provide the modularity, signal conversion, isolation (protecting the patient from voltages), and compact feature density to take patient monitors, bedside monitors, instruments and similar products down to the next level.
Portable patient monitors must be small, very lightweight and draw very little power to run continuously for hours on an internal battery. They must interface to small to mid-size LCDs preferably with LED backlight instead of CCFL, and share data and generate alerts over the hospital’s secure wireless network. Sensors and transducers in the form of attached probes supply analog voltage waveforms (DC to several kilohertz) to be captured and displayed on the monitor, and any irregularities need to trigger alerts and alarms.
The electronics must fit into a cavity inside the enclosure that is essentially the dimensions of the LCD and just several inches deep. The depth is large enough to allow the monitor to sit on a bedside table or a counter without easily tipping over. So rather than a large flat custom motherboard assembly, a stack-up of several boards better fits the rectangular prism cavity. Pin header connectors on the boards allow just the needed I/O to be cabled to external connectors.
Until recently, the size, weight and power draw of x86 embedded processors kept them away from these designs. The combination of new off-the-shelf low-power embedded x86 SBCs and Pico-I/O modules allows a complete monitor solution to be developed, utilizing robust PC networking, graphics and audio circuitry, yet providing additional expansion and customization opportunities for the OEM to differentiate.
Developers would like to leverage the robust desktop PC platform for shorter development cycles, long-term code maintainability and ever-increasing OS features. RISC-based designs typically require greater up-front design and tool costs, which pay for themselves years later in per-unit cost savings only after thousands of units have shipped. Due to cost and time-to-market considerations, developers’ needs carry much more weight in architecture decisions now. Operating systems like Linux and Windows Embedded Standard 7 (WES7) can be scaled down to a footprint appropriate for a lightweight portable device, and yet still offer the luxuries of robust desktop-class operating systems. All that’s needed is an off-the-shelf embedded computer with a flexible expansion interface for Pico-I/O, and design cycles can be reduced substantially while desktop-style features can be introduced into this product category.
Advances in x86 processors, including low-power Intel Atom and VIA Nano CPUs, combined with a new Pico-I/O offthe-shelf analog and digital I/O card ecosystem based upon USB, make it finally feasible to reduce size, weight, power and cost of off-the-shelf x86 building blocks in order to meet all major requirements of portable patient monitors.
At the heart of Pico-I/O is its standardized Stackable Unified Module Interconnect Technology (SUMIT) expansion interface. In late 2007 a group of embedded SBC and I/O manufacturers formed the Small Form Factor Special Interest Group (SFF-SIG) to help proliferate the success of USB-based industrial I/O into deeply embedded applications. SUMIT is the latest, smallest, stacking form factor for embedded I/O since the PC/104 standard. Created for the long lifecycle high-reliability embedded systems market, SUMIT features 52-pin fine pitch 0.635 mm connectors from Samtec’s high-speed board-toboard family with built-in ground plane. A board-to-board mated pair (one connector on the SBC, the other on Pico-I/O) forms gas-tight reliable connections over shock and vibration without the concerns of thin gold plating rubbing off of gold-plated card edge mezzanine cards.
Figure 1: At less than 2.9” x 2.4”, Pico-I/O is the tiniest and lightest stackable I/O standard. The SUMMIT I/O connector is on the bottom edge.
In addition to four USB channels, the SUMIT-A connector shown at the bottom center of Figure 1 also brings out standard PC buses including a PCI Express x1 link, LPC Bus, SPI Bus and I2C / SMBus, all in the lowest pin count stackable standard on the market to conserve space. PicoI/O cards are available with serial ports (UARTs), analog in/out, digital I/O, input and output isolation, relays and counters/ timers. The size, only 60 x 72 mm, puts Pico-I/O at exactly half the area of the previous smallest stackable I/O standard (Figure 2). Up to four Pico-I/O modules can be mounted together, and more if some of the additional SUMIT buses are used. The I/O cards and SUMIT-expandable SBCs provide for end-to-end USB full-speed and high-speed compatibility.
Interfacing to USB
While USB has greatly simplified the way peripherals attach to desktop and laptop PCs, its use in the small form factor embedded arena is just emerging. Fortunately, USB data acquisition (DAQ ) “dongles” that attach to PCs are growing rapidly in all types of environments from factories to warehouses to labs. The benefit to the medical community is a wealth of proven, rugged, reliable USB analog and digital I/O from the industrial automation market. The proven circuits and x86-hostbased device drivers carry straight across to the long lifecycle embedded computer market, as long as a mezzanine-style mounting is available to eliminate the USB cable while moving the I/O inside the system as required for medical patient monitors.
Figure 2: Space-saving yet stackable, Pico-I/O provides sufficient inputs and outputs with- out undesirable bulk and weight.
USB DAQ devices are perfect for a variety of applications requiring monitoring, control and industrial serial communications. USB is by far the most popular and compatible standard data interface for directly connecting to PCs. New features are added and tested in hours or days, not months. Initial proof-of-concept testing, demonstrations and application development are immediate, starting with a standalone USB DAQ dongle connected to a laptop computer via a USB port.
Figure3: A terraced approach with vertical headers simplifies headers while reducing overall volume occupied.
USB is the preferred I/O interface because of its popularity and ease of use. Unlike a bus, USB can be used in a star configuration where each I/O board does not have to be together or share the same bandwidth. USB 2.0 easily has the data bandwidth and latency to handle analog sampling at a mere kHz rate. Also, all USB dongle products can interface with all PCs, SBCs and even microcontrollers that support the USB standard. When it’s time to finalize the new patient monitor, the dongle is replaced with the corresponding Pico-I/O card and the laptop is replaced by a mobileor ultra-mobile-based embedded SBC, leaving just the mechanical design for mounting the LCD, backlight, boards, power supply, speaker and external probes connectors.
Pairing Pico with the Appropriate Platform
Although a custom motherboard can be designed with a SUMIT expansion interface for Pico-I/O, new small form factor x86 SBCs are coming along that would make most designers take this option and stick to core competencies—their medical application.
As shown in Figure 3, the Via C7-based EPIA-P710 Pico-ITXe SBC (bottom) has both SUMIT-A and SUMIT-B expansion connectors. Pico-I/O modules are stackable for easy installation into OEM equipment and eliminate the labor and stabilization required with vertical plug-in boards. Products based on the Pico-ITXe specification act as the perfect base board, taking advantage of an intelligent board layout that greatly aids both heat dissipation and stackability, all within a remarkably small footprint. Intel’s processors and chipsets are just now reaching the small size and integration needed to fit on this SBC size. The Pico-ITXe Specification is also available from the SFF-SIG.
The Pico-I/O module draws all required power from the SUMIT connector of the embedded computer. A USB power switch limits the entire current draw to 500 mA per the USB standard. The Pico-I/O size specification (60 x 72 mm = 4320 sq. mm) is exactly half of the PCB area of the popular PC/104 (90 x 96 mm = 8640 sq. mm) embedded board standard. The small size and easy connection makes the unit an excellent choice for a variety of embedded applications such as mobile, robotics, kiosks, and embedded medical and machine equipment.
As an example, the Pico-II8IDO4A (by Acces I/O Products) is an OEM USB solution for adding embedded reliable and robust multifunction I/O capabilities to any embedded computer supporting a SUMIT expansion interface. Featuring four solid state FET outputs, eight optically isolated digital inputs and two high-resolution analog inputs, the unit is the smallest of its kind for multifunction control and monitoring using USB. The FET outputs can switch customer supplied voltages from 5 to 34V, at up to 3A. The outputs are deenergized at power-up to prevent an unintended control output signal. The output connections are available via a 16-pin IDC vertical header type connector.
Figure 4: SUMIT’s USB interface and a USB-equipped microcontroller bridge medical I/O to embedded SBCs.
The digital inputs accept AC or DC signals as high as 32 volts and are interfaced via a 26-pin IDC-type vertical header. In addition, jumper selectable filtering per input channel provides for AC or voltage transients. The pinout allows a simple accessory cable to interface to one of the many available external screw terminal boards, or go cable-less and use a direct plug-in screw terminal like P/N TBK-26. Two analog inputs are also available on the 26-pin connector for a well-rounded multifunction compact PICO solution.
Embedded Software to Boot
As an embedded operating system with rich GUI, file system, peripheral and connectivity features, Windows XP Embedded, along with its replacement, the new WES 7, can be reduced in memory footprint to keep down the cost of a flash-based system, while easing the utilization demands of the modest-performance low power and ultralow power processor series (below 10 watts). For efficiency, the Pico-II8IDO4A utilizes a high-speed custom function driver optimized for a maximum data throughput that is 50-100 times faster than the USB human interface device (HID) driver used by other USB-based acquisition products. This approach maximizes the full functionality of the hardware along with capitalizing on the advantages of high-speed USB 2.0. Linux support is also available, and all source code, for all operating systems, including drivers, utilities and sample programs—even the firmware source!—is always provided.
As conveyed by the block diagram in Figure 4, this example Pico-I/O product (Figure 1) taps the ubiquitous USB 2.0 microcontroller market for low cost and power and easy SBC interfacing. Two single-ended 16-bit analog inputs can be used for monitoring vital signs, with a sample rate of 4000 per second and a voltage range of 0 to 5 volts. Eight non-polarized “digital” inputs can handle 0 to 31 volts DC or even AC rms, making interfacing to sensors and transducers straightforward. Any voltage below 3.1V is interpreted as a logic low (0) while 3.1-31V is a logic high (1).
The four digital outputs are implemented with FET N-Channel high-side switches using an external power source to switch even demanding loads with a level of 5 to 34 volts at 2 amps, even 3 amps peak for 50 milliseconds. These can be used to turn on and off local low voltage DC power sources, or drive motors, LEDs, buzzers or alarms.
Multifunction analog input modules, digital I/O modules, counters, timers and serial ports are among the many PicoI/O modules entering the market from several manufacturers. Signal conditioning including filters and voltage dividers can be found, and vendors are willing to customize to meet specific requirements. Compared to previous design methodologies such as full custom RISC-based or full custom carrier boards for computer-onmodules, tweaking off-the-shelf modules is a small order. Waveform generator circuits for ultrasound can be implemented on a Pico-I/O module.
Multiple peripherals such as POS, barcode scanners, scales, date-entry terminals, data acquisition (DAQ) modules and automation equipment can now be recognized and used on a single USB port. It is now easier than ever to add serial ports and serial devices to any application with the troublefree plug-and-play features provided by the USB standard.