Copyright © Shimmer 2017
Realtime Technologies Ltd Shimmer User Manual
All rights reserved Rev3p
50
detailed operational information, training material and errata on components designed into
Shimmer.
6.2.1. Radio Communication
One of the key functions of the Shimmer board is its ability to communicate as a wireless platform.
Shimmer uses a Bluetooth Radio module.
Bluetooth (IEEE 802.15.1)
Bluetooth is a low-cost, low-power, robust, short-range wireless communication protocol which was
initially founded by Ericsson in 1994 to replace traditional mobile phone and computer cables with
wireless links. It operates in the license free 2.4 GHz ISM (industrial, scientific, medical) band with a
short range (power-class-dependent: 1 metre, 10 metres, 100 metres) transceiver in each device.
With the introduction of the (EDR) Enhanced Data Rate feature [1], devices can communicate with
each other at up to 3Mbps. The Bluetooth special interest group (SIG) was founded in 1998 by
companies such as Ericsson, Nokia and Intel and the core system consists of an RF transceiver,
baseband and protocol stack. Bluetooth radios are designed for busy environments with many users.
Up to eight Bluetooth devices can communicate together in a network called a piconet. The piconet
is a point to multipoint network consisting of one master and up to seven slave devices. Multiple
piconets can coexist and join together to form scatternets. Bluetooth uses 79 1MHz channels to
transmit data. Interference between other ISM band devices (802.11 and 802.15.4 devices) and
other Bluetooth piconets is minimised using frequency hopping spread spectrum (FHSS), where the
carrier is rapidly switched (hops) among the 79 available channels. The frequency hopping sequence
is controlled by the master within the piconet. Other Bluetooth interference reduction techniques
include adaptive power control, Channel Quality Driven Data Rate (CQDDR) and Adaptive Frequency
Hopping (AFH) [2]. Extensive documentation and analysis of Bluetooth and its applications can be
accessed from the Bluetooth SIGs website at www.Bluetooth.org.
Microsoft Windows currently only supports a single Bluetooth Piconet, limiting users to seven
simultaneously attached devices. Linux support multiple Piconets and exposes the entire Bluetooth
stack in open source software, for users interested in doing advanced or special purpose
development with Bluetooth.
The Shimmer platform uses the Roving Networks RN-42 [3] Class
2 Bluetooth module to communicate via an integrated 2.4GHz
antenna. This module was found to be well engineered and very
configurable [4], reliable and robust. This module contains a full
Version 2 Bluetooth Protocol Stack and supports the Serial Port
Profile which facilitates rapid application development. The
Bluetooth module is connected to the MSP430 directly via the
USART1 serial connection. It can also be controlled by ASCII
strings over the Bluetooth RF link. The RN-42 has a range of more than 10 metres (33 feet) and the
transmitted power can be adjusted depending on the application distance. The system has seventy-
nine channels with channel intervals of 1MHz and offers a robust secure link via frequency hopping
spread spectrum (FHSS) and error correction schemes. Users can expect to communicate with the
Shimmer USART at speeds up to 230kbaud, with 115kbaud as the default and recommended value.
Roving Networks
TM
design
and manufacture sensors and
other custom platforms to
integrate embedded devices,
allowing access from
Bluetooth
®
enabled PCs,
PDAs, cell phones, and
networks. Further
information can be found at
http://www.rovingnetworks.
com/
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