introduction
The Internet of Things refers to the integration of various information sensing devices, such as radio frequency identification devices, infrared sensors, global positioning systems, laser scanners, etc., with the Internet to form a huge network. Then, all the items in life are included in the network for easy identification and management. In layman's terms, the terminal of the Internet is a person, and the terminal of the "Internet of Things" is an item. Each item has a CPU, a network address, and a sensor. The item and the item can also transmit information and send instructions. The main purpose is to By connecting all items to the network, the system can automatically, real-time monitor, identify, locate, track, and trigger events.
The rise of the Internet of Things has provided conditions for smart homes. How to simplify the IoT terminal device and finally develop a set of economical and practical smart home IoT platform that supports multi-terminal applications is a very meaningful and valuable work. Based on the Linux operating system, this system has developed a smart home control system that integrates wireless mobile networks and RFID devices. This system has functions such as smart meter reading, remote opening of electrical appliances, and remote sensing of radio frequency identification.
1 System Overview
The system uses S3C2440 chip as the main controller, and the operation interface is 4.3-inch touch screen. After power-on, the display shows the devices in the entire home system network, each device corresponding to an icon, including lighting control, fan, refrigerator, rice cooker, gas flow collection. Click the icon to go to the corresponding details bar of the device. Entering the lighting control interface, you can easily view the lighting conditions of each room in the home, or remotely control the lighting of each room through SMS; the gas usage can be easily sent to the relevant collection department; sitting in the office, a text message can be Turn on the rice cooker. The 2.4 GHz wireless RF transceiver chip nRF24L01 is selected between the devices in the home and the main control platform, which enables wireless communication between the home devices and the main control platform. The main control platform communicates with the external network, and adopts the MC39i GSM/GPRS terminal wireless module of Siemens AG of Germany. The gas flow measurement uses the MF4000 series gas flowmeter gas flowmeter of the United States Shengxiang Micro Electro Mechanical System (Shanghai) Co., Ltd. The block diagram of the smart home control system is shown in Figure 1.
Figure 1 Block diagram of the smart home control system
The embedded ARM2440 system development platform is the monitoring and management center of the entire smart home system. It mainly integrates wireless communication module, radio frequency identification module, infrared sensor module and touch display. On one hand, the master control platform can receive external commands (for example, mobile phone short messages) through the wireless module, and control the corresponding home equipment to work according to the instructions through radio frequency identification, for example, open a rice cooker, an air conditioner or a washing machine. On the other hand, the operation information of each household equipment can be received and collected by the RF module (for example, collecting gas readings, water meter readings, meter readings, etc.), after processing, the data can be sent to the embedded ARM2440 system development platform, which classifies the data. After that, you can select useful data to send to the corresponding company server (such as gas company, power supply bureau, water plant, etc.) to realize automatic meter reading.
Each home device in the smart home control system needs to be separately installed with a radio frequency identification module, which can realize short-range wireless communication with the embedded ARM2440 system development platform.
2 RFID module
The nRF24L01 is a single-chip RF transceiver that operates in the 2.4-2.5 GHz world-class ISM band. The RFID module can implement multi-machine communication, and the multi-machine communication adopts the method of frequency division multiple access, and only needs to configure addresses for different channels at the receiving end. The sender uses the corresponding address as the local address. When receiving data, you can know which channel's data is received by reading the relevant bits in STATUS. The RFID module includes: a frequency generator, an enhanced SchockBurstTM mode controller, a power amplifier, a crystal oscillator, a modulator, and a demodulator. The selection and protocol of the output power channel can be set via the corresponding SPI interface. The RFID module has low power consumption and consumes 9.0 mA when operating at -6 dBm in transmit mode and 12.3 mA in receive mode, with lower current consumption in power-down mode and standby mode.
The nRF24L01 can receive data of 6 different channels in the receiving mode. The structure of the nRF24L01 in the star network is shown in Figure 2. Each data channel uses a different address, but shares the same channel, that is, 6 different nRF24L01 can be set to transmit mode and can communicate with the same nRF24L01 set to receive mode, while nRF24L01 set to receive mode can be used. These six transmitters are identified. At the same time, all data channels are searched, but only
Figure 2 Structure of nRF24L01 in a star network
Receive data from one channel of data. The nRF24L01 records the address after confirming the receipt of the data, and sends an acknowledgement signal with the address as the destination address. The data channel 0 is used as the receive response signal at the transmitting end, so the receive address of the data channel 0 is equal to the address of the sender to ensure reception. Go to the correct answer signal.
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