Going wireless, now that's the key

01 May 2007

Trailing wires and limited range are things of the past, reports SAM FARNLEY, as he looks into input methods for the office, in the home and at leisure

Bluetooth can create and manage a network, or piconet, of up to eight devices, made up of one master and seven slaves. The IEEE802.15 standard provides for missed or corrupted packets to be resent, although the penalty is that resending slows the data transfer rate and increases power consumption. The master detemines the 1600 frequencies to be used each second across the nominal 2.4GHz band. It sends a 160bit package every 675ìsec, whether the target device is in use or not, to maintain the link within the piconet. The introduction of Bluetooth-enabled systems has seen office and home environments released from the bonds of wires and has changed the input landscape.

German engineering and Norwegian communications technology combine as computer input device manufacturer Cherry (www.cherry.de) uses ultra-low power transmitters and transceivers from Nordic Semiconductor (www.nodicsemi.no) in its Marlin wireless laser multimedia desktop
keyboard and mouse.

The nRF2401A transceiver and nRF2402 transmitter operate in the 2.4GHz ISM band and provide the slim keyboard with a range of at least 10m. The RF link is described as robust and not thwarted by obstructions such as desks, people and furniture. The wireless keyboard and mouse are immune to interference from other Marlin multimedia desktops, wireless LANs, Bluetooth and other 2.4GHz technologies that may be operating close by.

The nRF2401A is sensitive, to –93dBm and has true GFSK single chip transceiver with a maximum data rate of 1Mbit/sec. It has an integrated frequency synthesier, a power amplifier, a crystal oscillator and a modulator integrated into a single chip. Output power is programmable, as are frequency channels, through a three-wire serial interface. Current consumption is reduced to just 10.5mA at an output power of -5dBm and 18mA in receive mode. It has a data rate up to 1Mbit/sec and multi- channel operation and supports frequency hopping across up to 125 channels with a channel switching time of under 200ìsec. The transceiver is supplied in a 24pin QFN24 5mm x 5mm package. The nRF2402 2.4GHz transmitter is designed to complement its transceiver stable-mate and has all the necessary inductors and filters integrated into the chip, to save board space. To make a complete RF system, only a crystal and single resistor are additionally required. Current consumption is 10mA in transmit mode at -5dBm. It measures 4mm x 4mm.

The transmitter is configured via a standard serial interface and can replace IR and typical 27MHz wireless comms in most applications. It also features Nordic Semiconductor’s ShockBurst technology, where an onboard FIFO buffers data and transmits it in highly-efficient, in terms of power, short bursts. Cherry uses a proprietary channel-hopping algorithm that is claimed to guarantee transmissions are always made on interference-free channels.

Communications are also strengthened with automatic pairing of transmitter and USB dongle receiver via a 32bit identifier. Each transmitter periodically sends the mouse or keyboard data across a factory-determined selection of channels, from a possible 64-channel set. Encrypted data transfer protects all wirelessly transmitted keystrokes. The laser mouse operates on any flat surface and includes seven programmable function keys and an illuminated scroll wheel that also provides battery status information.

The ultra-low power transmitters and transceivers combine with low duty cycle operation to extend expected battery lifetimes. Depending on use, the keyboard’s two AAA 1.5V batteries can last for 12 months. The mouse has sealed-in AA rechargeable alkaline manganese dioxide RAM batteries that never need to be replaced, claims the company, as they are charged via a USB cable while the mouse is in normal use.

Keyboard functionality
There are ways of fitting more into less space as far as keyboards are concerned. Trackballs are often used to provide the pointing facility in areas where there is not much desk space.

Fitting a trackball into a keyboard is a popular solution, combining the two functions in one device. Access Keyboards (www.accesskeyboards.com), a UK company that supplies customised keyboards, also distributes stainless steel keyboards from Gertec. The metal IP65-rated boards for kiosks use Cherry switches and are intended for use in multimedia kiosks and internet terminals.

The keyboards are sealed to resist dust and liquid spill and, being stainless steel, provide protection against vandalism and heavy use. The key switches are rated for 50million cycles and the optional trackball has a life of 10million ball revolutions and a tracking force of 50g. The keyboard and trackball, where used, have PS/2 interfaces. There is an option to connect extra keys as well as output drivers for up to three LEDs.

Among the recent introductions, the company has launched a compact, custom keyboard with biometric access. The AKC098 is intended for use in banks as well as retail environments. It has a fingerprint reader alongside the conventional keys, which staff use to log on to the system. This is claimed to eliminate the problems of lost, swapped or stolen cards or personal identification numbers (PINs). The biometric element can also be used to trace transactions if necessary as well as improve security.

The biometric element is a U.are.U fingerprint reader module, manufactured by DigitalPersona. It has a USB interface and is compatible with Windows OS, including server versions. Users can be enrolled so that any finger or thumb can be used for log-on. The fingerprint data is stored as a binary number string, not as an image, which offers increased protection against identity theft.

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