NFC shell turns Nokia 3220 into an e-wallet

A near-field communication (NFC) device turns a Nokia cellphone into a practical tool in commercial and industrial settings for tracking assets, transmitting small data files or even auto-launching various phone-based tasks or requests. Designed to replace the outer case of the company's 3220 GSM handset, the NFC "shell" provides interesting new applications for a handset that began life as a pretty basic camera phone. This add-on device has similarities to the technology contained in a passive RFID, NFC relies on short-range communication, but also uses a tag to bring data read/write capabilities into play. But unlike the passive back-scatter identification techniques used in the railroad car tag, NFC enables two-way data transfer in a secure fashion.

Most important, the NFC shell is just one example of the far broader—and potentially expansive—application of financial transactions by mobile phone. If you have a Felica-enabled phone in parts of Asia, similar technology is at work, enabling the handset-based purchase of train tickets. Likewise, users of Exxon's Speedpass gas station payment key fobs are relying on the same concept: short-range data transfer between a powered reader and a passive tag.

To NFC-enable a 3220 handset, the user removes the original phone enclosures and replaces them with similar plastics that house an embedded circuit board containing the NFC circuits. A Java application called Service Discovery is added on top of the replacement hardware to get things going. The NFC shell kit from Nokia contains both the modified enclosure hardware and a set of four tags.

Once the Nokia NFC shell is put together, a user can read from or write data into the tags and share it with other NFC-enabled phones and devices. The Nokia manual cites data sets to be read, written or exchanged as "service shortcuts," which can be accessed, for example, by touching a tag to launch a call, sending a text message, bringing up a website or downloading a schedule. Other examples of use include grandparents placing a call by touching the phone to their grandkids' "tagged photograph," or electronically hailing a taxi by touching a livery's chipped business card. Micropayments—an electronic wallet in your phone—are of course also promoted as an application, though the largely nonexistent participation of commercial and infrastructure enterprises remains a barrier there.

Communication between the NFC shell and other devices occurs at 13.56MHz, the dominant globally standardized frequency for RFID applications. Communication typically requires proximity of less than 5cm between devices. A number of ISO, ECMA and ETSI standards govern the NFC and contactless smart-card infrastructure aspects of the design. The NFC Forum, an industry-driven consortium founded by Nokia, Philips and Sony, aims to ensure hardware-software interoperability.

But what really makes up the electronics solution? The answer lies in the relatively inexpensive silicon.

Starting with the supplied tag, a 45-by-45mm sheet of plastic hosts a nine-turn coil for the antenna, the leads of which connect to a diminutive 1mm² silicon chip from Philips. Its Mifare MF1 S50 RFID chip has 1Kbyte of E2PROM on board and uses the reader's transmitted RF energy in rectified form to power the circuit up during data exchanges. A mix of encryption, unique keys, multipass authentication and unique device serial numbers helps ensure security of the exchange.

A printed crossover on the tag's planar coil avoids multilayer circuits, which would drive up tag cost. Given that the semiconductor content on the tag is likely a dime or less, the carrier tag and device assembly likely contribute almost as much as the RFID chip itself to the total tag production cost.

Back in the add-on shell, a single PCB integrates six ICs and their associated passives. The electronics assembly also has an integral antenna, made from a circuit board trace, which loops around the board perimeter and is connected to the Philips PN511 transmission module. (This is Philips' name for the part, despite support for signal reception as well.) The PN511 contains the full 13.56MHz radio and a state machine-based digital section, which handles all data encoding, decoding, clocking, error correction and parallel or serial interface.

The PN511 communicates directly with the other major IC of the shell's electronics, an 8bit Atmel ATMega64 microcontroller. The MCU has on-board program and data memory along with a 10bit A/D converter, the latter of which probably goes unused in this design. To connect with the host phone, which uses a differing serial data voltage swing, an ST level-translating transceiver handles the communications interface between the Atmel controller and the 3220 handset. A 512Kbyte serial E2PROM is provided as well, presumably for storage of user-specific data, though its role in operating code storage-if any-to supplement memory on board the ATMega64 is unclear.

Beyond the controller, transmission module, interface circuit and E2PROM, only two small low-dropout regulators are present to handle localized power management.

Nokia's add-on product is really implementing in aftermarket form what is being integrated in growing numbers of Japanese handsets. In both cases, the handset serves as a platform for secure local communications to implement intriguing new use modes.

It may take a while for a full-blown ecosystem to develop for electronic-wallet applications, but the technology and cost structures are already in place to make it a reality, with some interesting steppingstone applications rolling out in the meantime.

David Carey
President, Portelligent

Keywords: Nokia   3220   near-field communication   NFC   RFID