What you need to know about BLE

Bluetooth (Bluetooth?) is a wireless technology standard that enables short-range data exchange between fixed devices, mobile devices and personal area networks. Today, Bluetooth is managed by the Bluetooth Special Interest Group (SIG), which is responsible for overseeing the development of Bluetooth specifications, managing certification projects, and maintaining trademark rights. Manufacturers' devices must also comply with the standards of the Bluetooth Special Interest Group in order to be recognized as "Bluetooth devices" "Enter the market in the name of ".

Generally refers to modules that support Bluetooth protocol below 4.0, generally used for transmission of relatively large amounts of data, such as: voice, music, etc. Classic Bluetooth modules are mostly used in Bluetooth audio modules, because audio requires large stream of data transmission, so it is more suitable to use classic Bluetooth.

BLE (Bluetooth Low Energy) is a supplement to traditional Bluetooth technology. Although BLE and traditional Bluetooth are both called Bluetooth standards and share radio frequency, BLE is a completely different technology.

BLE is not compatible with traditional Bluetooth. It is designed for small data rate, discrete transmission applications.

The Bluetooth band is 2400-2483.5MHz. This is the 2.4 GHz short-range radio band that is unlicensed (but not unregulated) worldwide.

Bluetooth uses frequency hopping technology to divide the transmitted data into data packets and transmit the data packets through 79 designated Bluetooth channels. The bandwidth of each channel is 1 MHz. Bluetooth 4.0 and later uses a 2 MHz spacing, which can accommodate 40 channels. The first channel starts at 2402 MHz, with channels every 1 MHz, to 2480 MHz.

Gaussian Frequency Shift Keying (GFSK) was the original and only available modulation scheme. Devices running GFSK can operate at base rate (BR), with instantaneous rates up to 1 Mbit/s; and enhanced data rate (EDR), up to 2 and 3 Mbit/s.

In Bluetooth wireless technology, the combination of the two modes (BR and EDR) is collectively called "BR/EDR radio".

Basic Rate: Profiles ensure interoperability between products from different manufacturers, another important feature of Bluetooth technology.

Enhanced data rate: Enhanced short-range wireless technology from Bluetooth version 2.1, making it easier to connect Bluetooth devices. Just turn on the device and select Add from the menu to complete the connection, and the device will automatically Search and connect automatically.

Advantages brought by this feature:

Bluetooth Smart is an innovative technology launched in 2010. This feature was first launched with Bluetooth core specification version 4.0 and is a Bluetooth low-power The brand name of the BLE consumer.

Bluetooth Smart not only has the characteristics of low energy consumption, it is also suitable for application creation. Energy consumption is lower because it uses far less power than other wireless technologies. It is suitable for application creation because the cost of using this technology to create applications suitable for Bluetooth smart sensors is low and the development structure can be flexibly selected.

The throughput of Bluetooth Smart is approximately 1 Mbps (depending on the application scenario). The throughput of Bluetooth BR/EDR is greater than 2Mbps, which is suitable for high-quality audio bit streams or other higher-bandwidth applications that require maintaining a connection.

Bluetooth Smart technology features:

Bluetooth Smart devices are mainly used in smart electronic products, including heart rate monitoring instruments, thermometers, blood glucose meters, smart wearable devices, tire pressure monitoring and e-cigarettes wait.

The official trademark is Bluetooth Smart Ready, which is a dual-mode radio frequency, indicating that it supports both traditional Bluetooth wireless connections and new Bluetooth low energy connections. Including electronic devices such as mobile phones, tablets, personal computers, set-top boxes and televisions that are at the core of the consumer connected world. These devices can effectively accept data sent by traditional Bluetooth products and future Bluetooth devices and BluetoothSmart devices and transmit it to application software. , thereby converting data into useful information.

At present, all relevant configurations of low-power applications are based on it. This configuration describes how Bluetooth devices work.

Descriptor: Describes the value in Characteristic (value range, value unit, or other descriptive information)

The Bluetooth device that provides data opens a Service to the outside world (distinguished by UUID , SIG has been defined), there is a set of Characteristic in the service for other connected devices to read and write.

The device (Client) that needs to obtain data connects to the device (Server) that provides data, obtains the service provided by the Server, and then can read and write the Characteristic value in the service. Client can also enable Characteristic notification. Whenever Characteristic changes, Client will receive notification.

The criterion for distinguishing central equipment (Central) and peripheral equipment (Peripheral) is whether a connection can be initiated. Devices in the central role can initiate connections to peripheral devices, allowing the device to support both modes simultaneously. Bluetooth Smart 4.1 starts supporting dual mode.

Pairing is mandatory for Bluetooth BR/EDR and optional for Bluetooth Smart. Normally, if an audio device (such as a headset) supports Bluetooth 4.x, it is compatible with the 4.x BR/EDR specifications and is not compatible with Bluetooth Smart. In other words, generally Bluetooth headsets must be paired before use.

The conventional connection process is:

Note: Peripheral devices are only allowed to be connected by one device, and the central device can connect to a limited number of peripheral devices

Server and Client The difference is: providing data as Server and consuming data as Client.

In the standard, both Central and Peripheral can be used as Server/Client. But generally the peripheral device acts as the server, and the central device acts as the client. After connecting, the Client can obtain data from the Server.

In order to accept connection requests at any time, a GattServer will be opened after the server is started.

Data exchange process:

Note:

I wrote a Demo based on Android, connect a watch with a mobile phone (can be transplanted to a mobile phone), and then click the watch application Send a message to the mobile phone.

If you are interested, you can take a look: