All About Bluetooth SMART
A Short History of The Bluetooth Standard
The evolution of the Bluetooth standard has enabled all kinds of exciting new applications, and the number of Bluetooth enabled devices worldwide has grown exponentially in recent years. Unfortunately, there has also been a proliferation in terminology, which is very confusing for someone new to the technology, and trying to find out what products might suit their application. So I will here try and provide some background on what has been happening with Bluetooth (and why), and which products you might want for your application.
What Is Bluetooth and How Does It Work?
Bluetooth was first launched as a "cable replacement technology". The idea was that devices that you connected together by cables – PC’s, phones, headphones, printers etc. – could be connected wirelessly instead, removing cable spaghetti over the desk.
How Did Bluetooth Get Its Name?
Why Was Bluetooth Invented?
Although there was much hype about the technology in the late 90’s, in reality, it was mainly used as an audio streaming standard, to connect telephones to headsets or car hands-free sets. One can debate why the technology was relatively slow to take off, but for me, the key reasons were.
- Relatively high power consumption, meaning devices needed regular recharging.
- Given that charging was often by USB, in many cases, it seemed simpler to plug something in and recharge and connect at the same time.
- The general purpose nature meant setting up devices could be fiddly, and sometimes didn’t work, putting users off. In the early days, interoperability from different vendors was hit and miss.
- Relatively low data rate meant cables still were the preferred solution in many use cases.
How Has the Bluetooth Standard Evolved?
Nevertheless, Bluetooth Special Interest Group (SIG) kept plugging away at it (or perhaps that should be unplugging away at it!). The standard had various revisions, and whilst I won’t go into all the technical details, the key steps forward were as follows:
- V1.0 – first release
- V1.1 - mainly fixing errors in the v1.0, and added a signal strength indicator to the standard.
- V1.2 - speeded up initial discovery and connection, increased data rate.
- V2.0 + EDR - major step up in data rate to around 2Mbit/s. Note that the EDR (enhanced data rate) is technically a "add-on" so a 2.0 device does not need to support this. So if you need it – check !
- V3.0 + HS - this allowed data rates of up to 24 Mbit/s, although confusingly, it doesn’t actually use Bluetooth to achieve this – the link is established via Bluetooth, but data transfer is then carried out by a 802.11 (basically WiFi) link. Also note that the HS, as for EDR is an “add-on”, so if you need it, check your device supports it.
What Is Bluetooth 4.0?
This is where the Low Energy/Smart stuff enters the story. The key motivation here was to overcome the barriers to adoption that were seen with the original standard – high power consumption, and fiddly setup.
What was recognised was that there were many applications where the data rate required would be quite low, but that a long battery life was required. An example in the consumer space would be a heart-rate monitor - which needs only to send a few numbers every second – but that few users would want to be bothered with charging every day. In the industrial market, a wireless sensor could be easily installed, but if the battery needed changing frequently, any advantage would be lost.
What Is Bluetooth Low Energy?
So Bluetooth Low Energy was born. It was similar to “classic” Bluetooth, but saved power by not needing a constant connection. Discovery and connection was also simplified.
So, we now have Bluetooth Classic, Bluetooth Low Energy, and also the High Speed add-ons. All of these together come under the "Bluetooth Smart" label. When it comes to devices however, some devices are Low Energy, some are classic and some are both. And to further complicate things, some devices “support” Bluetooth Low Energy, but aren’t actually low energy devices themselves. Confused? I will try to explain….
Bluetooth Low Energy "single mode"
This is a Bluetooth Low Energy device that only supports the Bluetooth Low Energy protocol. As such, it is a low power device. In practice this is what is used in your peripheral that you want to power for a long time of a simple battery, without the need for frequent recharges – your fitness tracker, or a sensor, or a mouse or remote control.
This is old style Bluetooth device, supporting the one of the earlier Bluetooth protocols. In practice, you would find this in an audio accessory, such as a headset, wireless speaker, or car connectivity module.
Bluetooth "dual mode"
This device supports both Classic Bluetooth and Bluetooth Low Energy – i.e. it can connect to either type of device. But it is not a "Low Power" device itself (as the need to support Classic means it cannot be). In practice, you find this kind of device in your phone, tablet or laptop (as these need to be able to connect to either type of device).
Bluetooth Classic devices can connect to each other, as can Bluetooth Low Energy "single mode" devices. And a dual mode device can connect to either. But please note that a Bluetooth "Classic" device cannot connect to a Bluetooth "Low Energy" single mode device.
What are Bluetooth Masters and Slaves?
You may also hear the terms "Master" and "Slave". In the Bluetooth protocol, one device is a Master, controlling when communications are initiated, and the other is a Slave, which listens but only "speaks when spoken to". Typically, the Slave is the node where power consumption is most critical. Somewhat confusingly, a node is not fixed in being a master or slave, it can change its role "on the fly", so it can listen as a Slave, then on receiving some data, change and become a Master.
The Master/Slave concept is used in both Classic and Low Energy Bluetooth, so a node being a "Master" or "Slave" does not tell you what type of Bluetooth is being used.
Continued Evolution of Bluetooth Low Energy
The standard has continued to evolve, although the fundamentals of BLE etc have not been altered.
V4.1 – mainly technical improvements, I won’t go into details.
V4.2 – more technical improvements, but the most significant is the implementation of IPv6, which will allow direct IP addressing of Bluetooth nodes.
V5.0 – With the launch of Bluetooth 5, Bluetooth® technology continues to evolve to meet the needs of the industry as the global wireless standard for simple, secure connectivity. With 4x range, 2x speed and 8x broadcasting message capacity, the enhancements of Bluetooth 5 focus on increasing the functionality of Bluetooth for the IoT.
What Type of Bluetooth do I need?
If your applications needs to stream audio, or be permanently connected, or has a very high data rate requirement then you need a Bluetooth Classic device.
If your application needs to run off a battery for an extended period, and has fairly low data rate requirements, you need Bluetooth Low Energy single mode device.
If you need to connect to different kinds of device, then you need a dual mode device.
If you want a very high data rate, and a very long battery life…..I can’t help you!
How low is a “Low Data Rate”, and how long is a “long battery life”?
I’ve used the rather vague terms “low/high” data rate, and “long” battery life. You may want more precision in these terms. Unfortunately, that is not so easy.
I can tell you that the maximum data rate (application throughput) under BLE is around 300kbit/s. However if your application were to run continuously at this data rate, then you would be having none of the"low energy" benefit of the protocol, as the device would be permanently on. For BLE, there is a trade-off between the frequency of connection + data volume sent and the power consumption.
At the other extreme, the idea behind BLE is that a simple application reading out a few sensors, and sending a few readings at an interval of a few times a second, a coin cell battery could last for months, and if the interval were increased to a second or more, the battery life could extend to years.
In between, the power consumption depends on how much data you are sending how often, and to a lesser extent, how much processing you need to do on the data before sending or after receiving it. There is no real substitute for prototyping a real world application, then fine tuning it to trade off performance and battery life.
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