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It’s now very easy to build short range two-way wireless data communication functions into a wide variety of equipment, using the Nordic family of UHF transceivers-on-a-chip. As well as the chips themselves, the company makes a range of pre-built evaluation kits for designers. Review by JIM ROWE One-chip Transceivers for easy UHF Data Communications www.siliconchip.com.au September 2002  67 A lthough digital mobile phones have grown in spectacular fashion over the last few years, the growth in wireless data communication has also been impressive. No doubt for the same reason, too: once you remove the need for a connecting cable, there’s greater convenience as well as many more potential applications. But the benefits of wireless data are by no means confined to high speed, wide bandwidth spread-spectrum technologies like Bluetooth and IEEE 802.11. A lot of short range applications can be served just as well by lower speed, lower bandwidth technology such as FSK (frequency shift keying, or ‘digital FM’). This can provide a very cost-effective solution for applications like alarm and security monitoring, home automation, remote control, shortrange telemetry, automatic meter reading, toys and so on. Putting this technology to work has been made particularly easy by Nordic VLSI ASA, a chip design and manufacturing company established in Norway in 1983. In the last three years, Nordic has released a range of complete single-chip FSK data transceivers and transmitters, which are designed to operate on frequencies in the UHF bands allocated in most countries for either ISM (industrial, scientific and medical) or LIPD (low interference potential device) use. Using these chips, a designer can provide their product with fully transparent short range two-way low speed data communications very easily. All that’s needed, apart from each chip itself, is a single crystal, a few SMD components and an antenna – which can be either an off-board quarter-wave whip or an on-board rectangular loop etched directly on the PC board. Even with the latter approach, the total board real estate required can be as little as 880 square millimetres (40 x 22mm). A good example of the Nordic chip range is the nRF401, a complete FSK data transceiver which can operate on either of two channels in the 433.05 434.79MHz ISM/LIPD band. Housed in a very compact (7 x 5 x 2mm) 20-pin SSOIC package, the nRF401 chip can handle data rates 68  Silicon Chip up to 20kb/s (kilobits per second). Its transmitter can achieve up to +10dBm/10mW of RF output (continuously adjustable down to -8.5dBm) with a deviation of ±15kHz, while the receiver has a sensitivity of -105dBm for a BER (bit error rate) of less than .001 at 20kb/s. The chip operates from a single DC supply rail of +3-5V, and the current drain in receive mode is typically only 11mA. The drain in transmit mode varies between 8mA and 26mA, depending on the RF output power level (which is set very simply via a single external resistor). The nRF401 also offers a ‘standby’ operating mode, where its current drain drops to a mere 8µA when the PWR_UP pin is taken to logic low level. It can become fully operational in either transmit or receive mode only 3ms after the PWR_UP pin is raised to logic high level, while switching between receive and transmit modes involves a setup delay of either 1ms (Rx to Tx) or 3ms (Tx to Rx), after the TXEN pin is taken high or low respectively. Thanks to its internal digital divider and PLL (phase-locked loop), the nRF401 needs a clock frequency of only 4.00MHz, which can be generated by the chip itself using a crystal and three other SMD components. Alternatively, it can accept a 4.00MHz clock signal from a micro-controller or similar, if this is already available. Either way, it can generate from the 4.00MHz clock all frequencies needed for FSK transmission and reception on either 433.92MHz or 434.33MHz, selected by taking the chip’s CS pin to either logic low or high levels. As you can see from Fig.1, the only other external components needed are two chip capacitors and a resistor for the PLL loop filter, a chip inductor for the VCO, a chip resistor from the RF-PWR pin to ground to set the RF output level, and some components to couple the chip’s push-pull RF outputs to whichever antenna is used. With an off-board whip antenna, the latter involves four chip capacitors and a pair of chip inductors, while an on-board loop antenna involves three chip capacitors and a resistor. The nRF401 needs no special setup or configuration and handles a standard serial bitstream so there’s no need for precoding of data. In fact it’s designed to act as an essentially ‘transparent’ physical-layer data interface, in either direction. UHF data communications couldn’t be much simpler! Evaluation kits easy To make it easy for designers to build the nRF401 into their products, Nordic provides two different evaluation kits based on the chip. Each includes +3V nRF401 DATA OUT VDD DEM LNA TX_EN ANT1 CH_SEL DATA IN PWR_UP ANT2 OSC PLL VCO PA VSS RF_PWR LOOP ANTENNA VCO INDUCTOR OSC XTAL PLL FILTER Fig.1: this is the circuit of the loop antenna version of the nRF401 evaluation kit. Three sizes of board are included, letting you determine optimum power output and current drain for a particular application. www.siliconchip.com.au In the LOOPKIT, you don’t get just one pair of modules, but THREE pairs – each with different loop sizes (18 x 10mm, 25 x 15mm and 35 x 20mm). This allows quick checking of the loop size needed for a particular application. are also used to set RF output power level in 6dBm steps from -8dBm to +10dBm, while another two bits are used to set the frequency of the 903’s clock output for driving an external microcontroller. Other features of the nRF903 transceiver include a higher maximum data rate of 76.8kb/s, plus GFSK (Gaussian frequency shift keying) modulation and demodulation capability. There’s an evaluation kit for the nRF903 too, complete with quite a lot of applications info. These appear to be the only full UHF data transceiver chips in the Nordic range, although a chip for the 2.4GHz LIPD band is apparently in the works and due for release soon. Transmitter range fully assembled PC board transceiver modules ready for operation, plus all necessary chip data and kit applications info. One is the nRF401-EVKIT, which provides two transceiver modules complete with matching ‘rubber ducky’ quarter-wave whip antennas. The other kit is the nRF401-LOOPKIT, which as the name suggests, provides modules featuring on-board loop antennas. However with this kit you don’t get just one pair of modules, but THREE pairs – each with different loop sizes, to allow quick checking of the loop size needed for a particular application. The three loop sizes provided are 18 x 10mm, 25 x 15mm and 35 x 20mm. Using one or the other of these evaluation kits, it should be very straightforward to check out the feasibility of providing your equipment with short range two-way data comms, and also to finalise the RF power levels and antenna size required. Other devices too The nRF401 isn’t the only data comms chip in the Nordic range. There’s also the nRF403, which is very similar to the 401 except for the frequencies of its two UHF channels. One is still in the 433MHz LIPD band but centred on 433.93MHz, while the second channel is centred on 315.16MHz. This frequency is also in an Australian LIPD band (304.05- 328.65MHz), but one allocated for use by personal safety alarms, car alarms and remote www.siliconchip.com.au door locking systems and home detention devices, with a maximum power level of either 10µW or 200µW rather than the 25mW limit applying to the 433MHz band. So if the nRF403 is used on this channel, its output power will need to be throttled well back. There’s an evaluation kit for this chip too, known as the nRF403EVKIT. This contains two transceiver modules with matching 315MHz helical antennas, plus all data and documentation. Another transceiver in the range is the nRF903, which comes in a 32pin TQFP package and offers more functionality than either the 401 or 403. The maximum power output of the 903 is still 10mW (+10dBm) but the chip can now operate on three different UHF bands: the 433MHz band, the 868-870MHz band and the 902- 928MHz band. Thanks to an inbuilt synthesiser, it can also operate on a choice of 256 channel frequencies in each of these bands. This means that the 903 can be easily programmed for operation on virtually any frequency in the Australian 433.05-434.79MHz and 915-928MHz LIPD bands, but its 869MHz option probably can’t be used here because this band is not allocated for ISM or LIPD operation. The nRF903 is configured with its band and channel frequency information by means of a 14-bit control word, clocked into the chip via a serial peripheral interface (SPI). Two bits of the same control word At present the other chips available are transmitters, rather than transceivers. These include: • the nRF402, which operates on the 433MHz band and is fully compatible with the 401 and 403 transceivers; • the nRF902, which comes in an 8-pin SOIC package and operates on any frequency in the range 862870MHz, with a maximum output of +10dBm and data rates up to 50kb/s; • and the nRF904, also in an 8-pin SOIC package, which operates on any frequency in the range 902- 928MHz, with a maximum output power of +1dBm (1.25mW) and a maximum data rate of 50kb/s. Local availability So if you need to provide some of your products with short range data communications capabilities, the Nordic range of single-chip UHF transceivers and transmitters is well worth checking out. They work on a number of our allocated LIPD bands, they’re easy to use and Nordic provides designers with a high level of support in the way of evaluation kits and applications information. They’re readily available in Australia from IRH Components, a division of Delta Electrical Group. You can contact them on 1800 252 731 (02 area call 9364 1766); or by email at sal10<at> irh.com.au More information is available at both the IRH (www.irh.com.au) and Nordic (www.nvlsi.no) websites. SC September 2002  69