Bluetooth 3.0
Older standards.
Bluetooth 4.0
The Bluetooth 4.0 standard is a Bluetooth standard launched in 2012. It is an upgraded version of Bluetooth 3.0. Compared with the 3.0 version, it is more power-saving, lower in cost, 3 milliseconds in latency, and has a long effective connection distance and AES-128 encryption .
The Bluetooth 4.0 standard includes two Bluetooth standards. To be precise, it is a dual-mode standard, which includes the Classic Bluetooth part (Classic Bluetooth) and the Bluetooth Low Energy part (Bluetooth Low Energy). These two parts are suitable for different applications or application conditions. Classic Bluetooth is developed and perfected on the basis of the previous 1.0.1.2, 2.0+EDR, 2.1+EDR, 3.0+EDR, etc. Bluetooth low power consumption is developed on the basis of Nokia's Wibree standard.
We generally refer to Classic Bluetooth as BT, and Bluetooth Low Energy as BLE. When the device supports Bluetooth 4.0, it is necessary to further confirm whether the device supports BT single-mode, BLE single-mode or dual-mode supported by both BT and BLE.
Put a software layer distinction between classic Bluetooth and BLE, the middle one is dual-mode. 
Comparison of the characteristics of classic Bluetooth and BLE: 
Android mobile phone Bluetooth 4.x is dual-mode Bluetooth (both classic Bluetooth and low-power Bluetooth), while some Bluetooth devices are single-mode for power saving (only support low-power Bluetooth) .
Classic Bluetooth BT
Classic Bluetooth modules can be subdivided into: traditional Bluetooth modules and high-speed Bluetooth modules.
The traditional Bluetooth module was launched in 2004. The main representative is the module supporting the Bluetooth 2.1 protocol, which was widely supported during the outbreak of smart phones.
The high-speed Bluetooth module was launched in 2009, and the rate was increased to about 24Mbps, which is eight times that of the traditional Bluetooth module.
Traditional Bluetooth has 3 power levels, Class1, Class2, and Class3, which support transmission distances of 100m, 10m, and 1m respectively.
Bluetooth Low Energy BLE
BLE technology uses a very fast connection method, so it can be in a "non-connected" state (to save energy) at ordinary times. At this time, the two ends of the link only know each other, and only open the link when necessary, and then in the shortest possible time. Time to close the link (up to 20 bytes per transfer).
Bluetooth low energy has no power level, and the general transmission power is 7dBm.
Classic Bluetooth, BLE, dual-mode Bluetooth selection
classic bluetooth
1) Voice transmission: such as Bluetooth headsets, Bluetooth speakers. Bluetooth is designed to transmit sound, so it is the best choice for close-range audio transmission. Now there are also WIFI-based audio transmission solutions, such as Airplay, etc., but WIFI consumes much more power than Bluetooth, and the device cannot be portable. Therefore, fixed speakers have WIFI, and mobile speakers such as earphones and portable speakers are all based on the classic Bluetooth protocol.
2) To transmit a large amount of data: For example, in some industrial control scenarios, if you use Android or Linux as the main control, and connect an external Bluetooth remote control device, you can use the SPP protocol in the classic Bluetooth and use it as a wireless serial port. The speed is much faster than BLE transmission.
BLE bluetooth
1), low power consumption, small amount of data, such as remote control (mouse, keyboard), sensor equipment (heartbeat belt, blood pressure monitor, temperature sensor, shared bicycle lock, smart lock, anti-lost device, indoor positioning).
2) At present, it is the most cost-effective means of communication between mobile phones and smart hardware. The straight-line distance is about 50 meters, and one AA battery can be used for one year. practical. Although the Bluetooth distance is a little closer, it is better than directly connecting to the mobile phone, and the price is super cheap. Taking indoor positioning as an example, every store in a shopping mall can hang a Bluetooth beacon to achieve indoor positioning of mobile phones with an accuracy of 10 meters. In the future, Bluetooth 5.1 can even achieve centimeter-level indoor positioning.
dual mode bluetooth
1) Smart TV remote control: Many smart TVs come equipped with remote controls with voice recognition, which require classic Bluetooth to transmit sound. And if you make complex buttons, such as functions that are not on the original keyboard, the classic Bluetooth HID button protocol will not work, and you have to use BLE as a private protocol.
2) Noise-canceling earphones: Many noise-canceling earphones use APP to adjust the noise-canceling effect, which is also a private communication protocol implemented through BLE.
Bluetooth 5.0
Compared with the previous generation of Bluetooth 4.2, Bluetooth 5.0 has a longer transmission distance and faster speed. The theoretical effective distance is 300 meters, which means that mobile devices in the entire home or office can be stably connected. The fastest speed is up to 2Mbps, making Bluetooth devices with faster response and higher performance more likely to be used. In addition, it also greatly enhances the data transmission of Bluetooth broadcasting, which can bring better prospects for commercial Bluetooth and make IoT applications that use Bluetooth as a standard more powerful.
Bluetooth SIG recently announced the launch of Bluetooth Mesh technology, which will break the "one-to-one" pairing between traditional Bluetooth devices and transform it into a "many-to-many" signal transmission mode. In addition to being applied to Bluetooth 5.0, it will also Extended to previous versions. The Bluetooth SIG stated that Bluetooth Mesh technology is a new network technology based on low-power Bluetooth technology, which will bring changes to commercial and industrial device networks, and will also make the existing Internet of Things technology more complete and stable.
The difference between Bluetooth 4.0 and Bluetooth 5.0 
In addition, attach a history of Bluetooth development:
Original: https://blog.csdn.net/qlexcel/article/details/116738423