Ppt on Bluetooth controlled industrial appliances

This article looks at the use of Bluetooth® technology in industrial automation applications to provide an alternative wireless data communications capability. It looks at the advantages compared to other wireless technologies and how issues such as interference can be handled. It covers the Stellaris Bluetooth development board from Texas Instruments as well as the Microchip RN-42, ConnectBlue OBS411 and RFM’s WLS1271 modules.

Although better known as a data connection technology in mobile phones, Bluetooth is well suited for wireless integration of automation devices in serial, fieldbus, and industrial Ethernet networks. It has not made dramatic in-roads into industrial automation in Europe, but using the experience and high volume production from the mobile phone business, IEEE 802.15.1 Bluetooth technology can provide small footprint, low power consumption, and cost-effective modules.

Bluetooth provides ready-made modules to simplify the development of a wireless data communications system on the factory floor, but there are some key issues to consider. Bluetooth can be used for two kinds of data network in this area, from providing a flexible user interface for machines to handling data direct from sensors to page link to an established wired network such as fieldbus or HART.

For non-mission-critical designs, Bluetooth is increasingly being used to access a built-in user interface based on WEB and WAP technology, mainly for maintenance and configuration. The point-to-point nature of the page link is well suited to particular applications such as on a sensor node that is periodically providing data from equipment. This is particularly useful in hard-to-reach areas where the sensor can provide key data on the health of the equipment and flag problems before they become critical.

For the more mission-critical applications, the radio page link reliability is key for deterministic behavior and real-time performance. Here, the important issues are the data rates, latency and interference with other Bluetooth nodes, other radio standards such as 802.15.4 ZigBee, and 802.11g and b Wi-Fi, which both operate in the 2.4 GHz band. Other radiating sources like certain types of machinery and microwave ovens operating at 2.4 GHz can also affect the performance of the Bluetooth link.

Another issue is communication error detection and automatic correction. The Bluetooth protocol includes key elements to make this as robust as possible while keeping down the cost and power consumption.

Specification

Bluetooth provides a range of 10 meters, but long-range modules can cover 200 to 400 meters or up to 1 km in free line-of-sight on a campus of buildings. A key element of the Bluetooth standard is Adaptive Frequency Hopping (AFH), Forward Error Correction (FEC), narrow frequency channels, and low sensitivity to reflections and multiple signal paths (also called multi-pathing).

The maximum data throughput for v2.0 of the standard is 780 kbit/s gross and this corresponds to around 700 kbit/s for the data payload. With the latest v2.1+EDR (Enhanced Data Rate), the maximum throughput is increased to 2.1 Mbit/s with a latency of 5 to 10 ms.

To avoid interference, the 2.45 GHz band is divided into seventy-nine 1 MHz wide slots and a new frequency slot is chosen each 625 µS. Each communicating pair of devices has its own frequency-hopping scheme decided when first connected and chosen, in order to avoid conflicts as much as possible. This technique minimizes possibilities for interference within a Bluetooth system and interference with the other radio-based systems.

For robustness, Bluetooth uses both Forward Error Correction (FEC) and packet retransmission. Two FEC codes are used, with a 1/3 rate code for the packet header and a 2/3 rate for the application data. This is a shortened Hamming code and able to automatically correct all one bit errors and detect all two bit errors.

For the packet re-transmission an ARQ packet retransmission scheme is used. Each packet payload contains a CRC checksum to check for errors and each transmitted packet contains an ACK/NAK bit to indicate the status of previous received packet. Retransmission is done if packets are lost or not acknowledged (NAKed).

To get the best data page link with minimal power consumption, Bluetooth uses Received Signal Strength Indicator (RSSI) power control. This is mandatory for the long range, high-power radios operating at 20 dBm, but is optional for the low-power radios at 0 dBm. Using the RSSI scheme makes sure that high power is not between a single pair of nodes, and means that independent Bluetooth networks in the same neighborhood will less likely interfere with each other. This helps keep the data rate higher, as the ACK packets will not be lost and have to be retransmitted.

A key difference from other standards is that Bluetooth also demands security features with 128-bit encryption that protects the data.

The complete protocol stack comprises both Bluetooth-specific protocols like LMP and L2CAP, and non Bluetooth-specific protocols like OBEX (Object Exchange Protocol) and UDP (User Datagram Protocol). In designing the protocols and the whole protocol stack, the main principle was to re-use existing protocols for different purposes at the higher layers, instead of inventing new protocols. This allows existing (legacy) applications to work with the Bluetooth technology and to ensure the smooth operation and interoperability of these applications. This means many applications already developed by vendors can take immediate advantage of hardware and software systems that are compliant to the specification.