ISM-Band Transceiver Simplifies Wireless Monitoring And Control

There are lots of short-range wireless technologies for implementing wireless data applications, like 802.11 Wi-Fi, Bluetooth, 802.15.4 ZigBee, and Ultra-Wideband (UWB). Even cellular technology can serve non-voice applications. But there are times when you don’t need the complexity of the protocol, the high speed, the networking options, or the cost. You may only need a direct point-to-point link or at most a simple star network.

You may even want to use your own simple but focused protocol unique to your applications. When that’s the case, consider using ISM-band (industrial-scientific-medical) radios. They operate on specific frequencies in the unlicensed spectrum, like 433 and 915 MHz in the U.S. and 868 MHz in Europe. Numerous single-chip radios are available for such applications.

Known for its widely used PIC embedded controllers, Microchip Technology also offers a line of ISM-band and ZigBee 802.15.4 radio chips. Its MRF49XA sub-gigahertz transceiver can operate on any of the above frequencies using frequency-shift keying (FSK). It also can support a data rate to 115.2 kbits/s in its basic digital mode and 256 kbits/s in its analog mode.

The transceiver’s direct-conversion architecture includes everything, including filters, on chip. An internal phase-locked loop (PLL) synthesizer with an external 10-MHz crystal sets the operating frequency. Automatic frequency control (AFC) keeps the transceiver on frequency. The receiver has its own low-noise amplifier (LNA) and sports a sensitivity of –110 dBm.

Both analog and digital received signal strength indicators (RSSI) are included. The transceiver has a power amplifier with a typical output of 7 dBm. Its dc operating voltage is anything between 2.2 and 3.8 V. Typical current draw is 11 mA in receive mode, 15 mA in transmit mode, and about 0.3 µA in sleep mode. The MRF49XA comes in a 16-pin thin-shrink small-outline package (TSSOP).

Designed to be used with one of Microchip’s 8-, 16-, or 32-bit PIC controllers, the transceiver interfaces through a typical four-wire serial peripheral interface (SPI) connection with an interrupt and a reset line. Nothing else is needed besides the 10-MHz crystal and the antenna with its matching network.

For applications development, the MRF49XA is available on a PICtail daughter card that plugs into one of Microchip’s development boards such as the PIC18 Explorer (see the figure). One is available for 433 MHz and the other for 868/915 MHz. A pair of boards is supplied for two-way testing. The development software lets you build your own protocol. Or, you can use Microchip’s simplified MiWi protocol as a starting base.

Chip samples are available now, with full production parts expected in July. Prices start at $1.63 in lots of 10,000.

LOUIS E. FRENZEL