Designing a wireless communication link into a product still requires solid engineering skills, but these days engineers don't have to become RF circuit design experts. In many cases, they can just drop a module into a circuit and get "on the air" quickly. To help designers, several companies offer development kits that ease the task of integrating radio-frequency (RF) communications in a product. Whether you must design a home security system or transfer data to a network, someone sells a kit that can give you a hand. RF devices in these kits range from simple radios to wireless modules that supply communication stacks, and general-purpose I/O lines, and that accept simple control commands.
To see what these design kits offer and how well they introduce developers to communication techniques and applications, Design News took a hands-on look. We approached five vendors and put their kits to the test to determine whether each served its purpose. Our lab work did not determine the suitability of a manufacturer's offering for specific types of applications. Based on our findings, engineers will benefit greatly when they buy one or two applicable kits and try them out.
The five kits we investigated include two that offer general-purpose communications, two that provide Wi-Fi (IEEE 802.11b) links, and one that contains ZigBee (IEEE 802.15.4) devices. Our descriptions below also cover one kit we saw demonstrated but did not test in a lab environment.
Other communication technologies, such as short-range Bluetooth (IEEE 802.15.1) and long-range Wi-Max (IEEE 802.16) offer alternative communication capabilities, but we didn't investigate them in this hands-on exercise. All the kits we tested operate within FCC-specified power limits and within the industrial, scientific, and medical (ISM) frequency ranges for unlicensed operations. Use of the kits requires that users know and follow FCC rules and regulations.
Digi International http://rbi.ims.ca/4391-557 Digi Connect Integration Kit (DC-WME-01T-KT; $249, Wi-Fi Kit)
The package sent from Digi included a development board, a Digi Connect Wi-ME module, an antenna, cables, a power cube, manuals, and a CD-ROM. The Connect Wi-ME module communicates with a host device over a serial port, and it provides five uncommitted I/O pins, a TCP/IP stack and an IEEE 802.11b (Wi-Fi) transceiver. The module mates with the development board and links to an access point (AP), typically a wireless router, on a network. So, if you need a Wi-Fi network connection, this kit can give you a head start. (Digi's kit does not include an access point.)The CD-ROM installed software and loaded an installation guide and documentation. After connecting the Wi-ME module to the board and applying power, I watched the board's LEDs, as instructed. A Status LED should have flashed as the module searched for and connected to the AP. Unfortunately, none of the board's LEDs flashed, and none was marked Status. It turned out the Wi-ME module contains two tiny LEDs, "Link Status/Integrity" and "Network Activity/Diagnostic," but neither the setup instructions nor the hardware reference manual identifies them for a Wi-ME module. This lack of detail in documentation frustrates me. Because I didn't view the development board from the antenna-connector side, I didn't see the LEDs. It turns out the Wi-ME module did detect the AP and the Network Reorienting the board made the Activity LED on the module visible, and it flashed as described. Next, I ran the Digi Device Discovery software from my PC networked with the access point. The software should detect the remote development board and report its characteristics. In this case, the software detected no active Wi-Fi networks in the vicinity and thus, no Wi-ME device. After several failed attempts, and with no help from the installation information, I eventually located "Release Notes" for the Discovery software on the Digi Web site. The notes warn against using a firewall between the Discovery software and the AP. Digi's set-up information, or a sticker on the CD-ROM should warn developers to check the company's Web site for up-to-date information, software changes, reported problems, and so on. To overcome problems with my firewall, I set up the Discovery software on an unprotected lab PC connected to my network, and that PC properly detected the Wi-ME module.The Discovery software's Web Management and Configuration interface let me check and change various parameters. Next, I decided to test remote control of the board and turn its LEDs on or off. Although documentation explains the development board's I/O ports and appropriate switch settings, nothing links that information to the configuration menus. I explored on my own and figured out how to control the I/O-port lines that drove the LEDs.The installed documents include code examples written in C/C++ for the Gnu Compiler Collection (GCC) that runs under Red Hat Linux 8.0, as described in the helpful ReadMe files. But developers who want to move beyond demonstrations and write code for the Digi modules should opt for the more capable Development Kit (DC-WME-01T-GN; $1495), which includes a complete suite of software-development tools. Digi's online support facilities include helpful technical documents and notes, and informative threaded discussions with users.My gripes with the Development kit center on several points: First, documentation should not skimp on the details. Things that seem obvious to manual authors often aren't obvious to users. Second, access to information on the accompanying CD-ROM should take place through a Web-browser interface. Third, more tutorial-level information that steps a potential developer through several simple applications will help attract users who need a bit of handholding.
DPAC Technologies Garden Grove, CA http://rbi.ims.ca/4391-558 Airborne 802.11b Wireless LAN Node Module Evaluation & Development Kit (WLNB-EK-DP001; $499, Wi-Fi Kit)
The DPAC kit aims to help developers make a Wi-Fi LAN connection and it furnishes a development board that includes a pre-mounted wireless LAN module (WLNB-AN-DP101). An antenna, serial cable, power cube, battery, and CD-ROM round out the kit's contents. Developers may not have an 802.11b Wi-Fi device available for experimenting, so DPAC also provides a Netgear Cable/DSL wireless router (MR814) as part of the kit.I have heard horror stories about installing wireless-network equipment, but the router installed easily and connected to my Comcast cable modem without any manual intervention. Next, I followed the brief quick-start guide and connected the development board to my lab PC. That setup went smoothly, too. The guide recommended using HyperTerm to communicate with the Wi-Fi module through a Telnet session between the lab (host) PC and the PC attached to the wireless router. That link also worked well.To understand the capabilities of the DPAC wireless LAN module, you must think of it as a communication processor, not just a 2-way radio. Each module includes a Web server, a TCP/IP stack, a command decoder, several I/O ports, and either a UART or an SPI interface. The availability of these serial interfaces eliminates the need for special driver software. Thus, you won't find C/C++ code examples in the documentation because you don't need them. Still, some "typical" settings and command set-up sequences might help developers.ASCII commands issued through a command-line interface such as HyperTerm control the module. The command, "wl-scan," for example, directs the module to scan for Wi-Fi access points and return information about any it discovers. Commands also control module I/O pins, and a command such as "adc-read g2," measures and returns a voltage from one of the Wi-Fi module's input pins. The development board routes I/O-port, communication, and control signals to connectors to ease engineering work. If you want to explore the capabilities of the development board, load the DPAC Airborne Evaluation Utility and print the user's manual for the evaluation kit. To learn more about the electrical characteristics of the Wi-Fi module and its commands, also print the Wireless LAN Node Module Data Book. The manuals--all on the CD-ROM--provide a wealth of complete and clear information about using the development board, the configuration software, and the modules. I recommend you print the manuals rather than try to browse through them using Adobe's reader.If you don't want to program communication settings through a command-line interface, use the module's built-in Web interface. I accessed the Web interface from my networked PC through the AP and the wireless link. After I made changes, I could save setup data in the module's internal flash memory or restore the factory default settings.Although the development board provided a Wi-Fi connection between my two computers and the cable modem, the kit will not connect to the Internet. The kit simply makes the Wi-Fi link. It's up to developers to determine what data gets transmitted and received and how an application that information.
The large Freescale ZigBee kit provides two MC13192-SARD accelerometer transceiver boards and three general-purpose MC13192-EVB transceiver boards. Each EVB board includes an RS-232 port and a USB port. Developers also receive a CD-ROM, batteries, power supplies, cables, an IEEE 802.15.4 ZigBee "sniffer" module and a background debug mode (BDM) programmer pod. A short-term version of Metrowerks CodeWarrior development studio software comes on a CD-ROM.The instructions explain the steps needed to set one SARD board to transmit x-, y-, and z-axis accelerometer data to a second SARD board that I connected to my lab PC. Graphic and numeric displays showed the results of moving the transmitter board, and flashing LEDs on the boards indicated they operated properly. This test confirmed I could run the embedded software and transmit a signal from one board to the other. To test ZigBee-communication range, Freescale provides another program that will run on either two SARD or two EVB boards. Although I followed the directions and the firmware seemed to load into the boards properly, I could not get the LEDs on each EVB board to display relative power levels. I also tried the software on two SARD boards with similar results. Talks with Freescale support people indicated a problem that required more investigations. I suggested the Freescale team download code using the bootloader and then examine or extract the code using the separate background-debug module. That way they would have independent download and upload paths to check for code errors. Freescale's engineers recommended I shipped my boards back to them for a closer look, so off went the boards. I received a new set of boards in return.It turned out the downloaded code was fine. The Freescale support staff determined I needed to enable a firmware-upload setting that would erase each board's Media Access Control (MAC) address. The manual does not include that step. After reloading the range-test software, the boards operated well and I measured a good signal out to several hundred feet over a clear line-of-sight path. The instructions leave a lot to be desired, though. In addition to the missing information about the software setting, file names did not match those on my disk and instructions lacked details.While waiting for a reply from Freescale's tech-support people, I skipped ahead to the Protocol Test Client (PTC) application (Section 5.8). Running this test requires loading new firmware into the transceivers, but the instructions do not explain which of the Embedded Bootloader's three listed PCT files get sent to a transceiver. Instead of taking a cut-and-try method, I skipped ahead to the Command Console software that lets developers send 801.15.4 commands directly to the evaluation boards. It seemed like a big leap from running demonstration programs to sending ZigBee commands to transceivers and I wonder how many people will "jump" across that chasm.One of the people I spoke with at Freescale said most developers skip the demonstrations and start to program with the "Wireless Z-Stack." A company called Figure 8 Wireless (www.figure8wireless) offers the Z-Stack software, essentially an application-programming interface (API) that simplifies ZigBee communications programming. Freescale also supplies a 90-day evaluation version of the Z-Stack that developers can download. For more information, go to www.freescale.com/zigbee. Click on Software Tools and look for the Protocol Stack listings. If you want to proceed without the Z-Stack, the CD-ROM that comes with the kit contains C/C++ source code for all the examples.The technical-documentation CD provides information about the SARD modules, but if you want to dig into the Freescale 802.15.4 MAC/PHY software--the software that links the transceivers to an application--you must go to the Freescale Web site, register, and download documents and code. Clicking on the SMAC Software and Applications link under the MC1319x Family (MC13191/92) Software and Development Tools heading creates a link that lets you download code files for seven example programs, all written in C. These samples start with a basic initialization of the MAC and culminate in a complete application that will receive data in a network. The Freescale documentation suggests downloading several manuals, which I did, just to see what they contain. The "802.15.4 MAC/PHY Software User's Guide" and the "802.15.4 MAC/PHY Software Reference Manual" are must-have documents if you want to learn more about how to use the transceivers in a simple application. The C-code can get complicated, so don't expect to master programming a ZigBee application in a few lab sessions. I applaud Freescale for making its demo source code available.The MC13193 kit comes with a receiver module and ZigBee "sniffer" software that monitors transmissions and decode them in several ways. When I encountered problems with the range test mentioned earlier, I used the sniffer to detect and monitor any ZigBee transmissions. The sniffer software, from Frontline Test Systems, proved easy to set up and use, although it took some experimenting to figure out how to view ZigBee packets. Unfortunately, Freescale did not supply information about the operating channel its modules use, so it took several trial runs to determine they use the 0x0b channel at 2405 MHz. After setting the operating channel, the sniffer detected the operating transmitter and displayed its output in several formats. Freescale's documentation does not explain the LED indicator on the sniffer module: red for "hardware can't send data" and green for "reading a packet." Frontline's technical-support person responded quickly to a telephone request for this and other information.The Freescale kit provides many opportunities to experiment, but the lack of tutorial information beyond the demonstrations will make it a difficult sell to developers new to ZigBee applications. Why not run developers through an example that illustrates how to modify existing code to control the LEDs on the development boards via a wireless link, for example? Even if you choose to experiment with the LEDs on your own, you won't find the schematic diagram for either the SARD or EVB circuits on the CD-ROM. I did find the diagram on the Freescale Web site, along with the PCB reference design, but I had to register and agree to a "license" before I could download it. Good luck reading the schematic's tiny print.The 13193EVK User's Guide refers to an evaluation-board reference manual, but a search of Freescale's Web site for the manual's part number--13192EVBRM/D--turned up nothing. Poking around the ZigBee portion of the site uncovered the manual as 13192EVBRM--no /D on the end. This sort of mismatched information turned up often in the Freescale manual, which gets low marks for usability. The Freescale kit suffers from documentation errors, lack of completeness, and little handholding for newcomers to ZigBee technology. If you can get by these annoyances, you'll find the Freescale kit has a lot to offer.
Chipcon http://rbi.ims.ca/4391-562 ZigBee Development Kit (CC2420 ZigBee DK; $5,000)
Chipcon offers several demonstration kits that incorporate the company's line of ZigBee communication chips. Instead of sending a kit, though, my Chipcon contact suggested I watch a demonstration of the CC2420 ZigBee Development Kit set up for a seminar. (Chipcon also sells less-expensive starter and demonstration kits.) Although I found the walk-through informative, nothing substitutes for getting your hands on real hardware.The kit comes with lots of hardware as well as development tools for the onboard AVR microcontroller. I saw several tests run and I watched a demonstration of the Chipcon ZigBee sniffer module and software. The sniffer produced a helpful display of ZigBee traffic and it breaks a transmission into easy-to-read MAC header, beacon, data, command, and other segments. The development boards worked as expected, but I missed having an opportunity to try them for myself. Chipcon recently acquired Figure 8 Wireless, the supplier of the Z-Stack software for ZigBee devices, so developers can take advantage of a Z-Stack API that works with the Chipcon boards. Figure 8 Wireless also offers a four-day course ($4995) on developing ZigBee applications. Please note: Chipcon Kit was not actually tested
RF communication cannot get much simpler or easier than the way Linx Technologies presents it in this kit, which demonstrates simplex (one-way) communication. This type of communication works well for alarms, remote controls, status monitors, data links, and similar short-range applications. The kit includes a receiver board, a transmitter board, antennas, batteries, a CD-ROM, and lots of documentation. The transmitter board provides two pushbuttons that control a relay and a buzzer on the receiver board. During testing, I measured a range of about 50 ft for the 1-mW transmitter after its signal passed through several walls. While testing outdoors, I placed the transmitter on a ground plane and received the signal at 300 ft over a clear line-of-sight path.
The single-channel transmitter operates at 916.48 MHz and its input accepts either an analog signal that produces an FM output, or a digital signal that produces a frequency-shift-keying (FSK) output. Linx Technologies specifies a maximum data rate of 56,000 bits/sec and recommends a format for digital data that will ensure the receiver locks onto a transmission. The transmitter and receiver chips send and receive what you give them. They do not apply a protocol or data encoding, nor do they perform any timing or error correction, they simply pass a signal.
Each board provides an RS-232 serial port for simplex data communication. The Linx Master Development 2.0 software includes a serial-communication program that lets one computer transmit data to another. I loaded the development software into two PCs, changed the jumpers as detailed in the user's guide, and transmitted typed character strings from one computer to the other. The receiver seemed to miss about every fifth or sixth string, but the errors may have more to do with timing of the Windows-XP operating system than with the radios. A bit-error-rate test over a 15-ft range, detected no errors during a 15-min experiment that involved transmitting about 1M bytes. In addition, the program transferred a small image flawlessly.Keep in mind that simplex transfers do not let a receiver request a retransmission of data. Developers can overcome errors by including error-detection and error-correction protocols or through redundant transmissions. In a meter-reading application, for example, the meter could transmit data 50 times in rapid succession to ensure the receiver picks up good data. And, transmissions could include error-detection bits. The receiver does not include a squelch circuit, so the receiver produces noise when powered and not receiving a signal. The development board provides an external squelch circuit, but I did not experiment with it. If you want to add a microcontroller or other circuit, each board provides signals at wire-wrap pins and an area for breadboarding.The kit comes with an extra transmitter and receiver chip and printed specifications and design information for each. Developers can use the kit's boards as reference designs for their own PCB layouts. Linx also provides a helpful 72-page booklet that describes FCC rules and regulations and the FCC approval process for unlicensed RF devices. I liked the completeness of this kit and think the Linx devices will serve well in many short-range applications.
When an application calls for basic 2-way communications that don't require a standard protocol such as ZigBee or Bluetooth, the MaxStream kit deserves your attention. The kit comes with a pair of XT09 long-range RF modules each mated to an XTIB-R interface board that connect to a device or computer through an RS-232/422/485 port. (Each module pair provides an unpackaged version of the company's standard XTend RF-modem.) Provided accessories include serial cables, serial-port adapters, power cubes, antennas, and a CD-ROM. I installed the X-CTU software from the CD-ROM and started it from my Windows lab computer. Hardware setup involved only connecting power and an antenna to each transceiver and checking DIP-switch settings. Software setup requires starting the X-CTU program and checking or setting serial-port information. To begin testing, I ran a range test that employed one transceiver at my lab PC and a remote transceiver connected to a serial-port loop-back connector (supplied). The PC-based unit transmitted strings of ASCII characters that the remote unit simply retransmitted. The PC-based software compared the sent and received data to detect and count any errors. Accumulating statistics indicate good and bad communications. (Packets of data include a header, application data, error-detection codes, and other information, not just the ASCII characters.)The range test ran error free in my work area, and walking with the battery-powered loop-back transceiver in hand produced a solid signal out to at least a 1000-ft (300m) over an RF path obstructed with trees, snow, and houses. Three green LEDs on the transceiver showed relative RF signal strength during the tests with one mW of power. Higher-power settings would have increased the range, probably to several miles. Unfortunately, I lacked a sufficiently large and unobstructed site for testing. (The transceivers will operate in a network or point-to-point configuration. I used the latter mode.)The X-CTU software provides a Terminal program that independently transmits and receives. To test this mode, I set up the X-CTU software on a second PC and replaced the loop-back connector on the remote module with a connection to that PC's serial port. Error-free communications took place from PC to PC. Transceiver control occurs quickly and easily through standard AT-modem-control commands or serial binary commands that establish encryption, power levels, module addresses, and so on. In operation, an XT09 transceiver module requires only a serial interface, found on most microcontrollers or microprocessors. Thus, the modules should easily drop into most designs that need RF communications. If you can operate without an industry-standard protocol, this type of device deserves a look. I wish I had more time to experiment with the many communication capabilities this kit offers.To simplify custom setups, the X-CTU software includes a Modem Configuration menu. Simply select the module in use and choose the parameters you want to modify. But before you change any settings, print the XTend-PKG-R RS-232/485 RF Modem manual that details the operation of the XT09 module, as it exists on the interface board. Each command reference includes a clear explanation, parameter ranges, a sample setting, a default setting and information about any acknowledgement bytes returned. If you scramble settings, an AT command string will reset and reprogram the default characteristics.Because the transceiver responds to 59 commands, it would help to have the manuals define and explain several fundamental command strings that let a pair of transceivers communicate under several conditions. Not everyone will want to use the factory settings, and learning how to combine commands in useful ways will help developers get started. Of course, they can always begin with the default settings and modify them one at a time, but that may waste time. (If you change one transceiver's settings, you may need to program the same settings in the other transceivers in your communication system.) Wi-Fi Devices
Wi-Fi devices can operate within a standard network and they provide a convenient way to let a product connect to a nearby local area network. The network could offer access to Internet services or corporate resources, or it might simply provide communication with a shared resource, such as printer, home-entertainment system, and so on.
· Easy to use, program, and drop into an application for point-to-point or networked communications.
· Clear manuals make setup easy.
· Good for high-speed, two-way communications that don't require industry standard compatibility.
Proprietary protocol, but most users won't care.
· Modules provide 256-bit AES security.
· Use this approach when you don't need a standard protocol.
· Easy to program.
· Modules use ASCII commands for programming.
· Programming examples would be a bonus.
· Would like to experiment more with this kit.
The Web version of this article includes more observations and comments about the Digi International, Freescale Semiconductor, and MaxStream kits. Also, we welcome your comments about adding wireless capabilities to a product. Have you used a development kit? What was your experience? Share your thoughts with Jon Titus at jontitus@comcast.net.
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