The Quatech Bluetooth CS0400-479 wireless serial adapter targets RS-232 cable replacement (a). It uses a standard DB9 connector. The antenna is internal. Quatech’s SS-BLT-400 is used for RS-232/422/485 interfaces in industrial applications (b). Transmit range is up to 300 feet under line of sight (LOS) conditions for both units.
Bluetooth has been around since 1998. That’s old for a wireless technology, and as a result it often doesn’t get the respect it deserves. Yet it’s probably the most widely used wireless standard today. Billions of Bluetooth radios are in operation worldwide. Last year, Bluetooth product vendors sold 1.7 billion devices.
Why is this amazing technology so taken for granted? Probably because it’s buried inside other products. It isn’t the mainstream communications link. Bluetooth’s most popular application is the wireless link in cell-phone headsets. Most smart phones and mid-range feature phones have Bluetooth capability, and each year more cars and trucks are delivered with Bluetooth hands-free kits.
Bluetooth has many other applications. For instance, it’s used as a wireless cable replacement. Quatech’s Bluetooth radios implement wireless RS-232 and RS-485 interfaces (see the figure). Audio streaming is another popular application, as in wireless speakers. Now the applications are expanding thanks to a new version called Bluetooth Low Energy (BLE) or version 4.0.
Standard Bluetooth
Regular Bluetooth (BT) operates in the 2.4- to 2.483-GHz industrial, scientific, and medical (ISM) band along with Wi-Fi and lots of other wireless technology. It uses adaptive frequency-hopping spread spectrum (FHSS) to minimize interference and improve link reliability. The basic hop rate is 1600 hops per second over 79 channels of 1 MHz each, providing a 625-µs dwell time for data to be transmitted.
Modulation is Gaussian frequency shift keying (GFSK). The basic data rate including overhead is 1 Mbit/s with a 723-kbit/s net throughput. A more recent version of Bluetooth uses modulation schemes like π/4-differential quadrature phase-shift keying (π/4-DQPSK) to get a data rate of 2.1 Mbits/s and eight-differential phase-shift keying (8DPSK) to achieve a 3-Mbit/s rate.
The transmission range varies with the power output. Three classes are defined. Class 3 uses 0 dBm (1 mW), Class 2 uses 4 dBm (2.5 mW), and Class 1 uses 20 dBm (100 mW). The most widely used, Class 2, provides a range up to about 30 meters. The higher-power version can reach up to 100 meters under the right conditions.
Bluetooth is also a personal-area networking (PAN) technology that can form networks. A Bluetooth network is called a scatternet, and one radio called the master can link up with up to seven other slave radios.
Special software packages called Profiles are available to configure Bluetooth radios for specific applications like wireless headsets, wireless speakers, or cable replacement. Profiles are available from the Bluetooth Special Interest Group (SIG), which promotes BT and provides BT testing and certification of products. The BT SIG has more than 14,000 members! How’s that for widespread acceptance?
Bluetooth Low Energy
The BT SIG approved Bluetooth Low Energy (BLE) version 4.0 in July 2010. Only now are we beginning to see some real products, with more coming later this year. BLE is designed for ultra-low power consumption, and a typical transceiver is expected to run for years on a single coin cell. It targets ultra-mobile and portable applications in the medical, automotive, consumer wellness, smart energy, entertainment, home automation, security, and sports/fitness markets.
Cambridge Consultants is one of the initial developers of the BT standard. The largest BT chip maker, CSR, was spun out of Cambridge Consultants in 1998. Cambridge Consultants still performs contract research and development in BT for its corporate customers. Broadcom, CSR, Nordic Semiconductor, Qualcomm Atheros, and Texas Instruments all have BLE products now.
BLE is much different from the traditional BT. Significant changes have been made to simplify the design and optimize it for low power consumption. BLE still uses adaptive FHSS, but the number of hops is reduced to 43 from 79 and the channel width is now 2 MHz instead of 1 MHz. The net bit rate is now only 200 kbits/s, but the range is extended to about 50 meters. Transmit power is about 5 mW with a current drain of less than 15 mA.
BLE’s setup time is less than 3 ms. Standard BT setup time to form a link is as much as 6 seconds. The whole radio is designed for short bursts of data rather than streaming. BLE cannot handle audio at all, which is why it’s often combined with standard BT on the same chip. Many new profiles are being developed (see the table).
One interesting potential for BLE is remote control. Most remote controls for consumer devices still use infrared (IR), but much work has been done recently to move toward an RF remote for greater range and less directionality. A ZigBee profile called Radio Frequency for Consumer Electronics (RF4CE) has been in development but has yet to be widely implemented.
BLE may upstage RF4CE and ultimately become the new worldwide remote control standard. Perhaps it also could compete with the 13.56-MHz near-field communications (NFC) standard for use in credit cards and cell phones for wireless payments and money transfer. Stay tuned.
Bluetooth Special Interest Group
www.bluetooth.com