EDN hands-on project: Get a grip: connecting mobile devices

In today's fast-paced, competitive business environment, embedded-system customers have discovered the benefits of portable devices for remote monitoring, control, and data delivery. With a networked-computing device in the palm of their hand, users have the flexibility and convenience of mobility while interacting with any number of local or remote systems. A wireless connection also increases the apparent performance of a handheld device by providing access to remote data storage and computing power. With a central software-configuration-management system, you can even remotely update features, repair bugs, collect data, and enable new services throughout the product's life. The increasing demand for these new mobile devices leaves designers little time to develop products from scratch, so many are turning to reference designs, modified consumer-electronics products, and off-the-shelf development platforms to shorten project schedules.

Like any other project, wireless-device development begins with a survey of customer expectations and performance requirements. Careful analysis of the results may actually disqualify a device from the wireless-handheld approach. For example, the expected battery life may rule out some applications because of product weight or poor access to recharging hardware. The small, general-purpose display; tiny input area; and lack of a keyboard may also exclude some potential applications. The operational area may also pose problems with RF-type communications due to interference, weak signals, multipath fading, line-of-sight obstacles, crowded airwaves, and any number of similar factors that can induce errors into the digital bit stream. A wireless-communications link may not meet the data- rate, response-time, cost, or reliability expectations of your project. The recent northeastern US power blackout rendered many wireless devices useless because of disabled channel infrastructure or system overloads. Many projects also require failsafe operation that is hard to guarantee with a wireless connection.

One of the earliest decisions in a wireless design is to determine the best network-communications approach to exchange data and commands. Short-range wireless networks include Bluetooth and 802.11 variations; longer range connections require dedicated transceivers or cellular data transmission. The most widely used wireless LAN (local-area network) is based on the IEEE 802.11b specification. Also known as Wi-Fi (wireless fidelity), 802.11b operates in the unlicensed 2400- to 2483.5-MHz ISM (industrial, scientific, and medical) frequency spectrum with data rates reaching 11 Mbps, depending on distance, interference, and traffic. With a maximum range of about 100m, 802.11b uses Ethernet protocol and CSMA (carrier-sense, multiple-access) with collision avoidance to allow multiple users to share the same spectrum. Unauthorized users can easily penetrate 802.11b networks unless you incorporate local security provisions, such as a virtual private network or the WEP (Wired Equivalent Privacy) encryption standard. WiFi5, the 802.11a standard that the IEEE released in 1999, is just now reaching the consumer market and uses a 5-GHz carrier frequency to prevent interference with many consumer devices. The 802.11a standard uses OFDM (orthogonal frequency-division multiplexing) as a modulation scheme and provides maximum data speeds of 54 Mbps. Another standard, 802.11g, is a 2.4-GHz, 54-Mbps wireless-networking technology with a reduced range but better interoperability with existing 802.11b devices.

If your wireless range is less than 10m, you might consider a PAN (personal-area network), such as Bluetooth, which can support a data channel, as many as three simultaneous voice channels, or a combination voice-and-data channel. Bluetooth also operates in the 2.4-GHz ISM band and targets low-cost, low-power applications. Bluetooth transceivers used a binary FSK (frequency-shift-keying) modulation technique that operates at 1 Mbps; however, the protocol overhead results in a maximum data rate of approximately 720 kbps per channel. For a long-range connection, some form of cellular or satellite communications is necessary. For example, CDPD (cellular-digital-packet data) is a specification for supporting wireless access to the Internet and other public packet-switched networks at data rates reaching 19.2 kbps. CDPD supports packet-switching, so a persistent link is not required, and multiple users can share the same channel. Although monthly data-access fees may be approximately $50, CDPD provides coverage throughout most of the nationwide analog cellular-phone system.

Today's digital telephone systems are ideal for long-range wireless data communications. CDMA (code-division multiple access) is one of the most widespread cellular technologies, and several large carriers, such as Sprint and Verizon Wireless, use it. CDMA is a second-generation technology in which the frequency of the transmitted signal hops according to a defined code, and only a receiver following the same set of frequencies can detect it. In addition to voice services, many operators provide CDMA circuit-switched data connections at 14.4 kbps or high-speed packet-data services at 153.6 kbps. GPRS (General Packet Radio Service), another packet-switched service, allows you to send and receive data over the worldwide GSM (Global System for Mobile) communications voice network. GSM uses a variation of TDMA (time-division multiple access) and operates in the 900-, 1800-, or 1900-MHz frequency bands. GPRS offers as much as 115 kbps, depending on the network availability, channel-coding scheme, and terminal capability.

In addition to the networking choices, designers have multiple options for handheld hardware, including consumer PDAs, smart cell phones, reference designs, and commercial development kits. Off-the-shelf PDA or cell-phone devices may eliminate the hardware development and turn the project into a strictly software task. However, many vendors want to differentiate the look of their products or have special-purpose requirements that commercial hardware cannot satisfy. If your wireless-handheld project includes both hardware and software design, one of the best ways to get started is to purchase a development platform with working electronics. The development-platform strategy allows both the software and the hardware teams to work in parallel for the shortest project schedule. To investigate project savings, I evaluated one of the latest development platforms from InHand Electronics. Its Elf3 board-level platform incorporates Intel's new Xscale micro-processor along with new power-management technologies that promise to greatly extend battery life (Figure 1).

InHand bases its development platform on its Elf3 single-board-computer reference design, which you can purchase in volume to further simplify device construction. With numerous expansion options, the Elf3 provides for extended display support, onboard Bluetooth and GPS modules, and memory expansion to as much as 32 Mbytes of flash and 64 Mbytes of SDRAM. The board also provides zero, one, or two PCMCIA slots for wireless networking, mass storage, data acquisition, or other plug-in peripherals. In addition to the single-board computer, the development platform comes with a 320×240-pixel display with a touchscreen, a null modem cable for connection to a host PC, a power supply, and a software CD. The Elf3 platform comes preloaded with either the Microsoft Windows CE .NET or Linux operating system, sells for $3495, and includes six months of customer support.

I selected the Windows CE .NET operating-system option, which requires Microsoft's embedded Visual C++ 4.0 for application development on the host PC. Embedded Visual C++ includes a complete desktop environment for creating applications and system components for Windows CE .NET-powered devices and is available free from Microsoft's Web site. The only problem was the size of the download: 333 Mbytes for the base compiler and 28 Mbytes for a required service pack. Because my satellite service provider has a fair-use policy, it took several days and a download manager to complete the data capture. You can bypass the lengthy download by ordering Microsoft's Windows CE .NET evaluation software CD for $3.95 plus shipping and handling.

You may need to purchase Microsoft's Platform Builder 4.1 software if you plan to develop drivers or create custom builds of the Windows CE operating system. Although InHand provides a couple of stock Windows CE operating-system images, you will need Platform Builder if you want the smallest footprint. I decided to work with the standard operating system and skipped the Platform Builder installation. The Embedded Visual C++ compiler also requires a software-development kit that describes which APIs (application-programming interfaces) are available for each unique Windows CE platform. Installing the software-development kit allows you to develop and debug software applications for the Elf3 from within the Visual C++ integrated development environment. Finally, I had to install Microsoft's ActiveSync to synchronize and update files on the development platform. The last step before power-on was to set up my PC's COM1 port to communicate with the development platform. A few settings in Window's HyperTerm terminal-emulation application, and I was ready for power. Although the download process took several days because of data limitations, the actual software setup took only a few hours following InHand's user's guide.

Hardware setup consisted of plugging in the "wall-wart" power supply and connecting the null-modem cable between my PC and the platform's serial port. When the development platform boots, it outputs status and version messages via COM1. The platform comes preloaded with InHand's version of the Windows CE .NET operating system and performs a screen-calibration sequence on initial power-up. It stores system-calibration factors and temporary files in DRAM, and you must restore these files each time you disconnect power from the device. Batteries that permanently retain DRAM data typically power fielded handheld devices. After screen calibration, the standard Windows CE start-up screen appears; it includes general-purpose applications, such as Internet Explorer, WordPad, and system settings. In a typical handheld-device software configuration, the device would power up to a custom start screen unique to the application.

Development and debugging of Windows CE applications via embedded Visual C++ is similar to performing those tasks in standard Windows applications. The main difference is that you download applications via a serial port, and the integrated development environment communicates with a debug-monitor program executing on the Windows CE device. This debug-monitor program allows breakpoint control, variable-value retrieval, and general-information exchange. I was able to easily create and modify a simple "hello-world" application using a template supplied as part of the embedded Visual C++ environment (Figure 2). The development device automatically downloads code modifications just a few seconds after any recompilation.

My final test was to add wireless capability by setting up a local 802.11b network between my PC and the Elf3 platform. I used a ZyXel Communications ZyAIR B-1000 wireless-LAN access point connected to the PC's Ethernet port and a wireless PC Card plugged into the Windows CE device. Although I easily configured this setup on the PC side, I had trouble finding a Windows CE .NET driver for any of the 802.11b PC Cards that I had on hand. A quick call to InHand produced a Lucent Technologies WaveLAN card that is compatible with the Windows CE .NET built-in 802.11b driver. The system recognized the WaveLAN card as a plug-and-play peripheral, and I was able to wirelessly connect to the Internet.

Although most wireless designs require a 32-bit processor to deal with the networking-software complexity, development platforms are available for smaller CPUs. For example, Iosoft offers a low-cost 802.11b development kit for designers of deeply embedded 8- and 16-bit systems (Figure 3). Providing a reference design for wireless devices, the kit provides a pc board with a PIC18xxx family microcontroller, flash memory, an in-circuit debug connector, and Ethernet, linked to a commercial PCMCIA card for the 802.11b wireless network. The development board provides access to Microchip Technology's PICmicro microcontroller analog and digital I/O plus an I²C interface. The software-protocol suite includes provisions for an HTTP Web server that supports multiple connections, forms for remote configuration, and dynamically updated HTML Web pages. As supplied, the Web server automatically provides an example Web page showing Wi-Fi network and channel ID with the dynamic status of the wireless link using the signal-strength indication that the PCMCIA card provides. Although a small recurring software license is required for production devices, the ER22 development kit costs just $290.

Another approach to wireless-device development is to start with a reference design. Texas Instruments offers a wireless handheld design that not surprisingly maximizes the use of the company's silicon. The WANDA (Wireless Any Network Digital Assistant) reference PDA integrates multiple wireless connections in a single device (Figure 4). Powered by Microsoft's latest Windows Mobile operating system, WANDA integrates 802.11b wireless-LAN, Bluetooth, and GSM/GPRS technologies to enable simultaneous phone calls, Web browsing, mobile commerce, wireless printing and headset listening, and integrated multimedia applications. To enable applications such as streaming video, audio, mobile-commerce, and location-based services, the design includes TI's OMAP1510 dual-core application processor, which combines the TMS320C55x DSP core with an enhanced ARM925 processor. The specification features 32- or 64-Mbyte flash memory, 64-Mbyte SDRAM, a 240×320-pixel QVGA transreflective display with touchscreen, and an 800×600-pixel digital camera.

In a similar vein, Intrinsyc Software offers the microPDA, a wireless, handheld device with fully integrated voice, data, Internet, and multimedia capabilities that you can use as a reference design or as a product-development platform. The heart of the microPDA is a single-board computer that supports several processors, including the 400-MHz Intel PXA250 XScale CPU with 64 Mbytes of SDRAM and 32 Mbytes of flash. The system includes a color TFT(thin-film-transistor) VGA touchscreen with backlight, integrated GSM/GPRS triband communications, Ethernet, Bluetooth, USB and IrDA communication support, plus a VGA-resolution camera. The PDA also provides a Compact flash slot, an MMC (Multimedia Card), and a SD (Secure Digital) card slot for the addition of further peripherals and functions. The microPDA comes with your choice of preinstalled operating systems, including Windows CE.NET, Windows Mobile 2003, and Linux. The microPDA development platform costs $3000.

With a handheld product, the simplest approach to wireless connectivity may be an off-the-shelf network module. DPAC Technologies recently introduced a line of Airborne modules that include a radio, a baseband processor, an application processor, and software, for a complete Web-enabled Wi-Fi subsystem (Figure 5). The 38×27×12-mm module features a built-in TCP/IP stack, RTOS, and application software to provide embedded devices with instant LAN and Internet connectivity without special programming of the module. You perform the only required configuration through DPAC's custom HTML interface. An integrated Web server makes it easy to remotely monitor and control any device using a standard browser. Airborne modules will be available in the fourth quarter of 2003 at prices of less than $80 (10,000).

As technology-savvy customers push handheld devices toward ubiquitous connectivity, designers are seeking short cuts, such as reference designs, development kits, and customized commercial hardware to accelerate the product-development phase. These low-cost, off-the-shelf products, designs, and tools give ample justification to consider integrating wireless networking into your next mobile design.

Author Information

You can reach Technical Editor Warren Webb at 1-858-513-3713, fax 1-858-486-3646, e-mail wwebb@edn.com.