 Intelligent
Bluetooth Modules make wireless design simple
Wireless connectivity has always been seen as difficult.
It needed the black art of RF design, plus significant
engineering design to develop communication protocols.
For that reason wireless has only been adopted where
it was absolutely necessary for a design. Today
that has changed. A new generation of easy-to-use
Bluetooth modules is attracting attention from
designers who want to get rid of the cables tethering equipment
together. Having a “drop-in” module that
is already pre-qualified is letting designers ask
the question “What happens if I get rid of
the cable”. The answer is that new functionality
can be added to designs, making them cost effective
and differentiating them from competitor’s
products. Forget the everyday existence of Bluetooth
in phones, PDAs and PCs, it’s already breaking
out of these mass markets into areas as diverse as
EPOS “Chip and Pin” terminals, Automotive
diagnostics, Medical Equipment, Telemetry and Building
Automation.
TDK is
a market leader in Bluetooth technology, designing
and manufacturing Bluetooth products for
the PC and mobile phone industry. However, the
barrier to Bluetooth design is a high one, which
has largely
confined Bluetooth adoption to high volume, consumer
goods. Converting the 2,500 odd pages of the Bluetooth
standard into a design needs a wide range of skills,
from RF design and layout, through to protocol
stack engineering and approvals. As a result
the typical
design cycle is 6 months with a Bluetooth approval
cost of $50,000. To open up the market to a wider
engineering base, TDK have
introduced a range of Bluetooth modules that are
complete in themselves
and have been designed to shrink that design cycle
to as little as an afternoon. They are also fully
approved as Bluetooth “End Products”,
which means that designers can ship them as part
of their products with no further Bluetooth approval
work.
Cable
replacement with wireless seems a simple concept.
When you look
at it in more detail complexity starts
to emerge. With a cable you know which two devices
are connected; with wireless that connection becomes
nebulous. Each device needs to know the device
at the other end. With a cable it’s easy – you
simply plug it into the appropriate sockets. In the
wireless world there may be many Bluetooth “sockets” so
a method of identifying the correct one is important.
Bluetooth adds extra versatility by letting the
connections be chopped and changed on an ad-hoc
basis as well as
extending the simple cable replacement concept
by allowing multiple devices to be connected simultaneously.
To make
these decisions, every Bluetooth device contains
a unique address. Each device can also be programmed
to show a “friendly name” to other devices.
The standard allows devices to make ad-hoc connections
by looking for the address or friendly name, or to
make more permanent connections by pairing. The standard
also introduces the concept of master and slave devices – masters
can control or interrogate multiple devices, such as
gauges. They can even swap roles of master and slave.
Such flexibility and versatility can make a Bluetooth
implementation seem daunting. In the PC world most
Bluetooth devices, such as USB adaptors and PC Cards
provide an intermediate interface known as HCI (Host
Connection Interface), and a separate software stack
on the device allows control of this via higher level
applications. This may work for complex, embedded devices,
but is totally inappropriate for general engineering
use.
To make
Bluetooth useable, TDK has
designed a module based around Cambridge Silicon
Radio’s (CSR) market
leading Bluetooth chipset. These modules include
a TDK developed virtual
machine embedded within the CSR silicon that provides
an “AT” style interface
to the engineer. This draws on over 8 years experience
of AT design and robust error handling protocols.
The “AT” command
set is well known as the basis of any telephony
modem. It requires simple text commands to be issued,
such
as ATD to dial a number. As well as the virtual
machine, TDK have embedded a complete Bluetooth
stack, along with Service Discovery, Dial Up Networking
and Serial
profiles.
The combination
of these means that designers can treat the TDK
module as a standard modem. The AT command
set provides new commands to access the Bluetooth
functionality, including commands for pairing, inquiry, authentication
and encryption. It also provides access to
general purpose I/O lines and two internal ADCs. 
| Why
choose Bluetooth? |
 |
|
Bluetooth was designed as a general purpose
radio. The aim was to provide multiple audio
links and to support most data applications
below 500kbps. It implements security in
the form of encryption and authentication,
and is optimised for battery powered devices.
|
Bluetooth was designed as a general purpose radio. The aim was to
provide multiple audio links and to support most data applications
below 500kbps. It implements security in the form of encryption and
authentication, and is optimised for battery powered devices.
The backing of major industry players has made Bluetooth into a comprehensive
specification. It can support real data rates of up to 723 kbps or
up to three audio channels for voice communications. Its adoption
in mobile phones and computing devices has meant that the silicon
cost has dramatically reduced. Today Bluetooth is displacing other
low cost, short range radios as the general purpose wireless link
of choice.
For industrial designers it also has the advantage of being one
of the most robust wireless protocols in general
use. Bluetooth uses
the 2.4GHz ISM (Industrial Scientific and Medical)
band, which is available as an unlicensed chunk of
spectrum worldwide. This is shared
with microwave ovens, 802.11 wireless LANs, video
senders, baby alarms and many more. To ensure a reliable
connection Bluetooth employs a
fast frequency hopping model, hopping randomly over
79 different channel in the band 1,600 times per
second. The Bluetooth standard has just
been updated to add Adaptive Frequency Hopping (AFH).
AFH allows a Bluetooth device to dynamically monitor
the status of its environment
and adjust the spectrum used to ensure optimal hopping
performance. The combination of these features means
that Bluetooth performance
will remain essentially unaffected as the 2.4GHz
ISM spectrum becomes more highly utilised. In contrast
other standards in the band will
suffer increasing levels of interference and see
a resulting degradation in performance.
| TDK's
Intelligent Bluetooth module |
 |
|
The Blu2i module provides a wide range of options
to suit many wireless applications. The module contains a complete,
approved Bluetooth processor and stack, a highly optimised
RF section with an omni-directional antenna along with a serial
interface, general purpose I/O and on-chip ADCs. Connection
to a host system is via a 40 way connector. |
The serial interface allows user programming of baud
rate, including non-standard rates. A useful innovation
is the fact that the ADCs and I/O can be accessed either by
the serial
interface, or directly over the air from another
Bluetooth device. This allows very elegant data monitoring
solutions to be designed. 
What differentiates the TDK Module from other
Bluetooth solutions is its flexibility and ease of
integration. The Virtual machine processes “AT” style
commands like a standard PSTN modem and controls the
Bluetooth stack
and operation. It becomes straightforward to connect
to other Bluetooth devices, discover what devices are
present and set
up and rip down audio and data connections at will.
Full details of the AT command set, along with applications
and getting started guides are available on the web at www.blu2i.com.
Range
Range is one of the most misunderstood aspects of Bluetooth.
The original specification defines a number of different
transmit powers for Bluetooth products, the highest
power being Class 1 with a maximum output power of +20dBm
(100mW)
and the lowest Class 3 (0dbM, or 1mW). These are typically
ascribed ranges of 100 metres and 10 metres respectively.
In reality the range is determined by the RF link budget – the
sum of the transmit power and receive sensitivity, taking into
account the losses within the components of the RF section,
as well as the efficiency of the RF matching. Because of the
problems in RF circuit design, some products that claim 100mW
output can exhibit open field ranges of just a few tens of
metres, whilst other products transmitting at 6mW can achieve
over 200 metres. The message is to be wary and to check range
empirically.
TDK has drawn on its RF component and design expertise to
incorporate one of the most efficient RF stages, along with
an onboard high-gain multi-layer ceramic antenna. The resulting
combination provides a useable open field range in excess of
200 metres. It also results in an antenna configuration that
is largely immune to placement, allowing the module to be located
close to ground planes with minimal effect on performance.
Approval
All Bluetooth devices need to pass through
a formal approvals process, defined in the Bluetooth
standard. This is required for a manufacturer to acquire
the right to use Bluetooth IP and use the Bluetooth name
and logo. In addition companies should become members
of the Bluetooth SIG, a process which is free of charge.
The Blu2i Serial Module circumvents the Bluetooth approval
process because TDK has qualified it as an end product.
This has been made possible by the embedded stack and upper
layer
AT command set. Most other modules do not contain this
degree of intelligence and require the manufacturer to perform
a Bluetooth
approval, which can be both costly and time consuming.
For a designer an end product approved module turns Bluetooth
into
a “drop in” solution.
Developer's
Kit
The best way to evaluate Bluetooth is to
try it out. TDK provides a range of Developer’s kits
which let you do exactly that. These provide a motherboard
for the module, along with level translation circuitry
and an RS 232 connector plus an external codec and headset
socket.
The aim of the Developer’s Kit is to get applications
up and running as quickly as possible. The ease of programming
via the AT interface means that it is often possible to
Bluetooth enable a design with an existing serial interface
in the course of an afternoon.
Applications
We have been surprised at the diversity
of applications for Bluetooth once designers perceive
it as a “drop in” serial cable replacement.
Many projects are already underway or shipping in
the following areas:
- EPOS – Chip and Pin and Printing
- Vending Solutions
- Automotive Diagnostics
- Medical Equipment
- Telecoms – utilising Bluetooth
audio headsets
- Telemetry and Data Logging
A range of applications,
reference designs and solutions are available on
the www.blu2i.com website
to help you discover ways to wireless enable your
design.
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TRBLU20-00800-01
|
Bluetooth Development Kit |
Order Code 508-9694 |
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TRBLU20-00100-01 |
Bluetooth Serial Module |
Order Code 508-9700 |
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