Serial Port Complete - Latest Microcontroller projects

Going Wireless

The physical network is based on the IEEE 802.15.4 standard for wireless per-

sonal area networks. The transmitters use spread-spectrum technology. In the

U.S., Zigbee systems transmit in the 2.4 GHz or 915 MHz bands. A transmis-

sion can travel up to 50 meters, and routers can extend the distance.

Zigbee supports multiple network topologies, including a mesh topology where

each node can communicate with any other node within range. In a Zigbee net-

work, one device is the Coordinator, which manages the network. The other

devices are either End Devices, which perform monitoring or control functions,

or Routers, which extend the range of the network and can perform monitoring

or control functions as well.

MaxStream’s XBee-PRO modem has an asynchronous serial interface and a

ZigBee interface. Data received on the asynchronous serial port transmits on

the ZigBee interface, and data received on the ZigBee interface is written to the

asynchronous serial port. A vendor-specific command mode and API enable

configuring the modem over the asynchronous interface.

For more about Zigbee programming, I recommend the book Hands-On Zig-

Bee by Fred Eady.

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Bluetooth (bluetooth.org) is a hardware and software standard suitable for a

variety of wireless applications. The interface supports secure transmissions at

low power and low cost. Devices can transmit data over distances of up to 100

meters and at speeds of up to 3 Mbps. Bluetooth uses the 2.4-GHz band with

spread-spectrum technology. Up to eight Bluetooth devices can communicate

with each other in a collection called a piconet.

Bluetooth Profiles define higher-level protocols for specific functions. The

Serial Port Profile supports COM-port emulation.

A7 Engineering, Inc. (www.a7eng.com) is a source for Bluetooth modules with

asynchronous serial interfaces. The eb501-SER module can interface directly to

an RS-232, 5V, or 3V asynchronous serial port. The device firmware supports

Table 8-1: Wireless systems can use standard protocols to carry data.

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Bluetooth 3M 100

Zigbee 250k 50, extendable with routers

Wi-Fi 54M 40 or more