Bluetooth - Introduction

Thanks to Bluetooth Application Developer’s Guide

Continuation...

Wireless connectivity offers us immense freedom and convenience. It allows us to perform tedious tasks with a minimum of intervention, allows some of our devices to have dual functionality, and makes the vast array of cables we inevitably always leave in the office redundant. Bluetooth technology "will" change the assumptions we all have about our electronic devices.With the cables gone, the idea of having a particular gadget for a specific job will no longer be relevant. With many of the devices already available to consumers, this scenario grows closer to reality every day.

Safety-critical

Although the Bluetooth specification with a frequency-hopping scheme which does provide robustness, it is still a serious consideration for some applications. Bluetooth technology should not be used for safety-critical applications where data absolutely must get through, because there is always a possibility of a burst of interference stopping the link. Interference can come from a variety of sources: microwave ovens, thunderstorms, other communications systems. There are other safety-critical applications where an unreliable link may be acceptable.

Connection Times

There are two delays in setting up a Bluetooth link. First, it takes time to discover devices in the neighborhood. In device discovery, a device sends out inquiry packets, and receives responses from devices in the area, then reports these to the user. It can take ten seconds to find all the devices in an area, and even then you will only find those devices which are willing to report their presence. Some devices may not be set to scan for inquiries, in which case you will never find them!

A second delay occurs when you set up the connection itself. Again, this can take up to ten seconds.This lengthy connection time means that Bluetooth devices are unsuitable for systems where a fast response is needed, such as automatic toll collection on busy roads.

Power and Range

Power is a critical consideration for wireless devices. With the cable gone, the subject of batteries is brought into focus, and the inevitable questions arise concerning battery life, standby time, and physical dimensions. Keeping the power consumption low is an important consideration.

The range of battery life depends upon the product functionality. Power consumption is much higher when either transmitting or receiving, so the longer you expect your product to be in these states the shorter the battery life. Clever power management design, battery monitoring and use of the Bluetooth power saving modes will all contribute to reducing power consumption.

The Bluetooth specification defines three power classes for radio transmitters with an output power of 1 mW, 2.5 mW and 100 mW.The output power defines the range that the device is able to cover and thus the functionality of your product must be considered when deciding which power class to use.