Introduction to Bluetooth

Updated 23 July 2017

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Nowadays, everything is going wireless. Phones, computers, game controllers, consoles, everything! Wireless technology has allowed us to use electronic devices with an untethered freedom which just isn’t possible with clunky cables hanging off your device. There are many forms of wireless connectivity such as Wi-FI, cellular data, Zigbee, however, one of the most popular and widely used wireless protocols is Bluetooth. Whilst the Bluetooth 5 standard was announced earlier this year (2016), we’ll be taking a look at using the Bluetooth 4.2 standard as it is most commonly available at the moment.

What is Bluetooth?

Bluetooth is short-range, wireless data protocol designed for sending and receiving data over a secure 2.4GHz network. It was originally conceived during the late 90’s as an in-house project at Nokia, however, it quickly spread to become a standard for wireless data. The first mainstream Bluetooth protocol was launched as Bluetooth 1.0 and has had several iterations through to the current Bluetooth 4.x and Bluetooth 5. Bluetooth 4.0 was important because it introduced the sub-standard known as Bluetooth Low Energy (also known as Bluetooth LE or BLE). Bluetooth 4.x is also known as Bluetooth Smart as it enables backwards compatibility for both traditional Bluetooth and Bluetooth LE.

Traditionally Bluetooth was designed to transmit large amounts of data over a short distance with products like hands-free headsets for phones, and speakers in mind. However, Bluetooth LE is a newer, low-power standard which uses the same carrier system and basic protocol, however, it’s designed for battery operated systems which only need to send small amounts of data to another device, using sleep mode in between transmissions, and is perfect for mobile, power-conservative devices. Bluetooth LE is also a standard feature of today’s smartphones and computers and because of the simplified nature of BLE, it’s much easier to setup communication with these devices.

What’s The Range of Bluetooth?

Traditional Bluetooth is divided up into 3 classes; 1, 2, and 3 with Class 3 devices having a range of roughly 5m, Class 2 devices having a range of 20-30m, and Class 1 of around 100m. Bluetooth 4.0 simplified things by removing the range limitation from the specification and simply allowing for the signal strength and receiver sensitivity to determine the range, providing that the regulations for radio-frequency transmission power aren’t exceeded. Generally speaking, though, most BLE devices should give a range of at least 50m, with some operating over 100m and the new Bluetooth 5 standard expects double the range of most Bluetooth devices.

Bluetooth is a packet based master/slave protocol which allows for up to 7 (Bluetooth classic) or an application dependant number of (BLE) slave devices to be connected to a single master device. This type of single master network is called a ‘piconet’. A slave device, also known as a peripheral device, can only communicate with a single master device, and cannot communicate with other slave devices on the piconet. If it wishes to pass data to and from other slave devices, it must go through the master.

Bluetooth piconet diagram

Bluetooth was originally designed to be used as a wireless solution for serial communication such as UART which makes it perfect for wireless communication between chips. Bluetooth LE is the perfect choice for most maker projects that don’t require high data transfer such as audio applications, as it makes it incredibly simple to transfer data packets and bytes. There are two main ways to use Bluetooth technology: GAP and GATT.

GAP: General Access Profile

To establish exclusive communication with a master (central) device, a slave (peripheral) device must first pair with that master to join/create the piconet as shown below with a GATT setup. However, before you establish this connection, a BLE device must advertise itself as available to other devices by transmitting an Advertising Data payload (required) and an option Scan Response payload. Both payloads can be up to 31 bytes of data, however, whilst the advertising data is transmitted constantly at a set interval to all other Bluetooth devices, the Scan Response payload can only be requested by a central device. There are many situations (Apple’s iBeacon technology for example) where you want a single device to transfer only a small amount of data (perhaps a sensor or location info) to any device around. You might have a small transmitter installed in a shop so that customers can easily view information regarding a product. You don’t want it to be exclusive between two devices, but available for all central-type devices to view.

GATT: General Attribute Profile

This is the connection type after a slave device has connected to a master device. The current Bluetooth standard defines a whole bunch of different device profiles that you can choose from, based on how your device operates. This profiles range from heart-rate monitors to Bluetooth keyboards and contains a bunch of pre-defined attributes that you can send. You can of course transfer custom data attributes, however, the definitions are designed to help standardise communication across current uses of BLE communication.

Ok Cool, How Do I Add Bluetooth To My Project?

Well, that was a brief explanation of how Bluetooth and more specifically Bluetooth LE work, but fortunately for us makers, we usually don’t need to worry about the nitty-gritty aspects of Bluetooth communication as there are plenty of Bluetooth modules which make it incredibly simple to get started with implementing Bluetooth communication into your project. In fact, unless you plan on delving down into the depths of embedded applications, pre-configured Bluetooth modules are the way to go. We’ll be taking a look at different Bluetooth modules, and which one is going to be best for your project in our ‘Choosing a Bluetooth Module For Your Project’ tutorial, so check that out, and if you have some projects that you’ve implemented Bluetooth in, we’d love to see them!

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