Design of smart home system based on nRF905

Abstract: The smart home monitoring and control system is built by nRF905, which connects the units and the main control unit to control the home security control, ambient temperature detection and air ventilation control. Users can use infrared remote control. Centralized controllers to control any of these units for easy control of the home environment.

Keywords: smart home; wireless networking; nRF905; security control

In the smart home, the digital home network is a communication platform installed in the home, which has the characteristics that the general communication network should have, and considers that the location where it is installed is ordinary private home and the user is an ordinary resident. Therefore, it also has its own unique needs and characteristics, including security, usability, reliability, flexibility, scalability, ease of use, low cost, standardization, small size, light weight and easy installation. The home network technology in the smart home system is mainly divided into two categories, one is wired home network technology, and the other is wireless home network technology.

With the development of wireless communication technology, wireless networks have an unparalleled advantage over wired networks in terms of communication range not limited by environmental conditions, short network construction period, low construction cost, easy maintenance, and good scalability. The network has become the first choice for the networking of smart home network systems.

1 Smart home system structure

The design is mainly composed of a temperature detecting unit, a Door Lock switch detecting unit, a ventilation and ventilation motor control unit, and an electric switch centralized control unit; each unit realizes centralized control through wireless technology networking; the wireless network is constructed using a token. The ring topology mode can avoid competition and conflicts of multiple 905 modules on the channel. The main control unit monitors and controls the running status of each unit based on the wireless networking. Users can also remotely access the smart home control system through Intemet/GPRS to view and control the devices. The system structure is shown in Figure 1.

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2 Wireless networking of smart home units

Since the nRF905 radio frequency chip itself does not have a networking protocol, in order to make the central control unit and each control node in the smart home form a complete communication network, and the system has at most one device (including the main control unit) at each moment. Data transmission (to avoid channel competition and conflict) requires a protocol to be written. In the design, the nRF905 wireless network networking mode adopts the token ring bus mode.

2.1 Data format transmitted by the system

The data format definition of the system transmission is shown in Table 1:

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Destination node address (4 bytes): This field is the address of the node to which the data is sent. The receiver identifies the field to determine whether it is the data sent to itself.

Source node address (4 bytes): This field is the address of the sending node. The receiving end identifies the data by identifying the field.

Token flag (1 byte): Used to judge whether the received frame is a token, a token reply, or a normal data frame.

Frame body (27 bytes): This field information is valid data.

Frame Check (1 byte): The transmitting node calculates a frame check sequence using a cyclic redundancy code (CRC) and stores the result in this field.

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