CN111953373B

CN111953373B - Broadcast type message communication device based on 433MHz

Info

Publication number: CN111953373B
Application number: CN202010795097.5A
Authority: CN
Inventors: 康金辉
Original assignee: Shaanxi University of Technology
Current assignee: Shaanxi University of Technology
Priority date: 2020-08-10
Filing date: 2020-08-10
Publication date: 2022-08-12
Anticipated expiration: 2040-08-10
Also published as: CN111953373A

Abstract

The invention discloses a 433 MHz-based broadcast message communication device, which comprises a transmitting terminal and a plurality of receiving terminals. The sending terminal consists of a PC terminal, a transmitting terminal MCU, a 433MHz serial port wireless communication module, a GPS receiver and special sending software running on the PC terminal. The invention adopts 32 frequency bands of 433MHz for communication, effectively avoids interference, and the unrepeatered broadcast using the wireless data transmission radio station can reach 8000 m. The communication message is encrypted by AES128 bit. The invention has low cost, reliable communication and adjustable communication distance, and is not dependent on the current mobile communication network and the Internet. The method is very convenient to apply to public message communication and emergency message communication in departments such as enterprises, governments, schools, hospitals, military affairs, fire fighting, public security, water conservancy, buildings, rural residences and the like.

Description

Broadcast type message communication device based on 433MHz

Technical Field

The invention belongs to the technical field of data communication, and relates to a broadcast message communication device based on 433 MHz.

Background

In one-to-many messaging, a relatively large number of mature schemes are involved. Such as traditional mobile phone short message group sending; widely used internet-based communications such as WeChat, QQ, etc.; the civil interphone communication with a certain frequency band is applied, and currently, the LoRa communication, the NB-IoT communication and the like are more in the field of the Internet of things.

It has the problems that: the mass texting relies on the signal of the network operator, and has a certain cost, and the security procedure is general. Although the communication based on the internet, such as WeChat, QQ is reliable at present, the QQ is more private, even if used publicly, depends on the internet, and the confidentiality is common. At present, the communication of the civil interphone is difficult if data communication exists while voice communication is carried out. Based on LoRa, NB-IoT and the like, data communication in the internet of things is applied, and some of the data communication also have encryption above AES128, although the features of one-to-many, ad hoc and the like are also provided, the application is not the scope of the present invention.

For example, in government departments, it is often necessary to issue public or encrypted messages to specific departments or groups of people to notify them of important matters or to perform conference notification. It would be convenient if there were a common display terminal on the desktops of designated groups in these designated departments. If the mobile wireless mode is used in an office hall and other occasions, if the mobile wireless mode is used for public information such as office guides, cautionary matters, even weather, temperature, traffic guides and the like, as the supplement of data, the mobile wireless mode is undoubtedly flexible at any time. If the encryption message transmission is in the unit or the department, the encryption message transmission in a wireless mode has certain confidentiality.

In schools, a large number of classrooms need a display terminal to display the utilization conditions of the classrooms when the classrooms are in class and activities are carried out. In a student dormitory, a public display terminal is required to display messages sent from a school, messages which are tied to students by the school, messages which are given to the students by a teacher, and the like. Such as informing students to attend an academic lecture, conference, etc.

In certain sectors of a hospital, there is sometimes a need to distribute hospital-wide public or encrypted messages, notifications. Sometimes it is necessary to inform certain department personnel to attend a meeting, a joint consultation. The display terminal with the text reminding function and arranged on the desktop of the office is convenient.

In some business and government sectors, there are specialized private networks for services. Many of the contacts inside are based on private networks. Some forbid internet access and even limit the use of the mobile internet. In this case, wireless-based encrypted messaging has the potential for applications.

In public departments of social services, such as fire control, public security, water conservancy, water supply and power supply and other departments, in emergency situations, a public receiving terminal installed in public places, offices, dormitories and other occasions is needed as a supplement to traditional communication. In an emergency state, an alarm system provided in a terminal system is important for urgently notifying a specific person to complete a certain event in minutes and seconds.

Disclosure of Invention

The invention aims to provide a 433 MHz-based broadcast message communication device.

The technical scheme is as follows:

a broadcast message communication device based on 433MHz comprises a sending end and a plurality of receiving ends.

The transmitting end consists of a PC end, a transmitting end MCU, a 433MHz serial port wireless communication module, a GPS receiver, a 4G/GPRS interface and special transmitting software running on the PC end.

The transmitting terminal has two modes, one is a broadcast mode, and the broadcasting mode can be wholly broadcast or locally broadcast; the other is a point-to-point mode, namely, data are sent to a receiving end of a specific address, so that messages can be issued to specific departments and specific crowds.

The transmitting end and the receiving end adopt a self-defined protocol method to carry out data communication, and the format is as follows: a receiver address (2B), a transmitter address (2B), a data length (2B), an urgency feature (1B), a response feature (1B), an encryption feature (1B), a CRC16(2B), a data header (5B), a time of day (12B), a data portion (nB) encrypted using the AES 128-bit algorithm.

The PC end is connected with the MCU of the transmitting end through RS485, and the special software for running the PC end is computer software which runs under Windows and has a message transmitting interface. The software has the functions of selecting group sending and sending an appointed address, selecting an emergency message and a common message, having the functions of responding or not, encrypting or not and the like, and finally transmitting data to the MCU of the sending end.

The serial port 1 of the transmitting end MCU is connected with the 433MHz serial port wireless communication module; the serial port 2 is connected with the 4G/GPRS interface; and the GPS receiver is connected through an RS485 adapter. The method has the function of encapsulating the message sent by the PC terminal software in the memory by the self-defined message protocol. The encapsulated data comprises date and time information obtained by decoding the GPS time service message. And connecting the packaged data packet with the 433MHz serial port wireless communication module in a serial port mode for transmitting.

The 4G/GPRS module is a module connected with the mobile internet and is connected with the transmitting end MCU through a serial port 2. A plurality of authorized mobile phone numbers can be connected with the 4G/GPRS module through 4G signals, transparent data is sent to the MCU of the transmitting terminal through specific software, the MCU is packaged with a self-defined message protocol in the same way, and finally the transmission is carried out. The method aims to ensure that authorized workers can use the mobile phone to remotely connect the 4G/GPRS module to issue messages to users of the home network, and the method is convenient to use in emergency.

The 433MHz serial port wireless communication module is a remote data transmission module based on a serial port and is connected to the transmitting end MCU serial port 1 through the serial port. Both receive and transmit. The communication rate is typically set to 9600bps, the air baud rate defaults to 2.5Kbps, and the communication channel is divided into 32 channels at intervals of 1M from 410 MHz.

The receiving terminal comprises a 433MHz serial port wireless communication module, a 7-inch serial port color screen, a receiving terminal MCU and an alarm unit.

The 433MHz serial port wireless communication module is consistent with the transmitting terminal.

And the serial port of the 433MHz serial port wireless communication module is connected to the serial port 2 of the receiving end MCU. And the MCU is used for receiving the wireless signals transmitted by the transmitter in a long distance and transmitting the wireless signals to the receiving end in a transparent manner.

And a serial port 1 of the receiving end MCU is connected with the 7-inch serial port color screen. And the serial port 2 is connected with the 433MHz wireless communication module, and the P1.0 port of the serial port is connected with the alarm unit. And the 433MHz wireless communication module transmits data sent to the local machine to the MCU of the receiving end, and the MCU of the receiving end decodes the sent messages according to a self-defined message protocol to obtain the data of each field. And decrypting the data part by using a decryption key stored in the receiving end MCU chip hardware, filtering illegal messages, and pushing the data to be displayed to a 7-inch color screen through a serial port 1 for display. Under normal condition, the message of the receiving end is displayed on a 7-inch color screen, under emergency condition, the receiving end sends out an alarm signal while receiving the message, if response is required in the field, the receiver responds to the sending end through a button.

And the alarm unit is connected to a P1.0 interface of the MCU of the receiving end. The LED flashlight has the functions of driving circuits, buzzer alarming and LED flashing.

The receiving end 7 inch color screen at least comprises a Chinese character hardware word stock of 6763 Chinese characters. In the message received by the receiving end, if the message is a Chinese character, the message is a Chinese character internal code coding mode. One Chinese character is represented by a Chinese character internal code mode of 2 bytes, and the mode greatly reduces the wireless data transmission quantity.

The data adopts AES128 as a symmetric encryption algorithm at the transmitting end and the receiving end. The encryption key and the decryption key are identical. The encryption method comprises the following steps: the encryption key and the program file of the transmitting end MCU are burnt into the single chip microcomputer together, and when the encryption key is encrypted, the program reads the encryption key as a constant to encrypt data; similarly, the decryption key and the program file of the receiving end MCU are burnt into the single chip microcomputer together, and when decryption is carried out, the program reads the decryption key as a constant to decrypt data.

The method for preventing the encryption key and the decryption key from being illegally read comprises the following steps: the MCU adopts STC15W4K32S4, the MCU has the hardware encryption function of the program file, the encryption principle is that the program file is encrypted by adopting a globally unique ID number when the MCU chip is manufactured through a complex algorithm, and once the program file containing a secret key is burnt into the MCU, the current technology and method cannot read and decrypt the program file. When the MCU normally runs, the program file stored in the MCU is automatically decrypted and normally runs, and the key stored as a constant can be read through the normal program file, so that the encryption and decryption processes are realized.

The method for preventing the program file from being illegally rewritten comprises the following steps: downloading password protection, wherein the running programs of the MCU at the transmitting end and the receiving end cannot be rewritten without a password.

Frequency range of 433MHz wireless communication module transmission: 410 Mhz-441 MHz, one frequency band every 1MHz, 32 frequency bands, and 8000m of non-relay broadcast by a wireless data transmission radio station. In order to avoid the illegal interference of the same frequency band 433MHz, the same channel, such as number 17, and the same address, such as (9999) data, the method adopted is as follows: in the data portion of the custom message protocol, a 5-byte header is defined, for example: "MNPQR". Even if the frequency, channel, and reception address are known, the illegal data is discarded because the decryption key cannot be obtained and the correct data header cannot be obtained. Thereby avoiding data interference.

Further, at the transmitting end, in a general case, the transmitting end MCU, the GPS (excluding the antenna), the 4G/GPRS module, and the ac 220V to +5V power supply module are all packaged in one housing. The USB-RS 485 module is independently arranged externally, so that the USB-RS 485 module can be arranged near a PC (personal computer), and the transmitting end is connected and arranged at a far position through an RS485 cable, so that a GPS (global positioning system) antenna and the wireless transmitting module antenna can be conveniently arranged at a roof and the like.

In the power supply part, a standardized industrial switching power supply is adopted to output +5V and 5A current, and the power supply part has the functions of lightning protection, short-circuit protection, good heat dissipation and the like.

The USB-to-RS 485 module adopts a photoelectric isolation type, and has lightning protection and strong industrial anti-interference performance. An industrial RS485 signal cable is adopted.

The external GPS antenna of the transmitting end requires a gain of more than 38db, a noise value of 1.5db, a standing-wave ratio of less than 1.5:1, circular polarization, an SMA interface antenna is adopted, the length of the antenna is at least 5m, and the GPS antenna is required to be installed outdoors in an unobstructed environment. Can receive big dipper and GPS signal simultaneously.

The antenna of the transmitting terminal 433MHz wireless communication module is also externally arranged, an outdoor glass fiber reinforced plastic omnidirectional antenna is adopted, the length of a feeder line is at least 3m, the antenna is vertically polarized, the gain is at least 5db, the impedance is 50 omega, and an SMA interface is adopted.

At the receiving end, under normal conditions, the MCU, the wireless communication receiving unit, the alarm unit and the like are designed and installed on a PCB, a power interface with a DC005 structure is provided, an ac 220V to +5V power adapter is used, external power is supplied, and a computer USB interface can also be used for power supply.

The receiving terminal is 7 cun color screens, provides four IO interfaces of +5V, GND, RXD, TXD, has functions such as can show full-color, characters and image. The length is 200cm, the width is 100mm, the PCB board at the receiving end is placed in a 7-inch color screen, the right side is provided with 12mm 5mm large keys, three keys are arranged in the vertical direction, and the three keys are respectively an emergency reply key, a display and a standby mode key. The bracket structure is designed to be inclined at 45 degrees and stand on the desktop.

The receiving end wireless module antenna adopts an external sucker antenna and is provided with an SMA inner pin interface, and the height of the antenna is 17 cm. Since 433M wireless signals are received, the antenna connected to the receiving end may be indoors.

Compared with the prior art, the invention has the beneficial effects that:

first, it can be widely used in various fields of social life. Such as government policy message distribution, the message may be distributed at multiple locations. Messages are posted in public areas such as parks, squares, communities, hotels, restaurants, and the like. The device can be normally used or emergently used in schools, hospitals, fire fighting, public security, water conservancy and power, communication, agriculture, transportation and other departments. Secondly, the cost is low, for example, the cost of the traditional enterprise-level short message exists, the short message can be used without application of a mobile network and the Internet, and because most of messages are text messages, the receiving end and the sending end have high speed based on text processing and low cost, dozens of hundreds of receiving ends have no influence except slight delay of communication. Thirdly, reliability, the current module without the relay band antenna has 2.5Kbps of air speed and almost no packet loss when the transmission distance is 8000 m. Under the general condition, the method is reliable in the complex environment of 5 km-6 km. When there is the one-level relay, can reach 12 ~ 15km. fourth, it is simple to operate, and the receiving terminal can be in public area, can also be at home at the office. Fifth, it is used as a supplement to the current local area communication. In emergency, the authorized user can use mobile phone to connect 4G/GPRS interface, and directly use broadcast message to issue data, that is, realize wireless issue of remote data. Of course, under normal conditions, the release can also be carried out by using a mobile phone to connect with a 4G/GPRS interface.

Drawings

FIG. 1a is a block diagram of a transmitting end of a 433 MHz-based broadcast messaging device in accordance with an embodiment of the present invention;

FIG. 1b is a block diagram of a receiving end of a 433 MHz-based broadcast messaging device according to an embodiment of the present invention;

fig. 2 is a flowchart of an embodiment of the present invention for providing a transmitting end MCU to encapsulate a data packet;

fig. 3 is a diagram illustrating an embodiment of an MCU encapsulation data packet at a transmitting end according to the present invention;

fig. 4 is a flowchart illustrating a receiving end receiving a data packet according to an embodiment of the present invention.

Detailed Description

The technical solutions of the present invention will be described in further detail with reference to the accompanying drawings and the detailed description.

To further illustrate the advantages of the present invention:

the experimental environment is as follows: the transmitting terminal is 30 meters away from the ground, the external wireless transmitting terminal is provided with an external sucker antenna, and the GPS antenna is arranged externally without shielding. The communication speed of the MCU and the serial port of the wireless module is 9600 bps. Air rate 2400bps, channel 17, transmit power 30db, transmit end address 8888, directional transmission mode, encrypted prefix 5 bytes, with CRC check. The packet load is 64 bytes, the load contains a counter, the transmitting end continuously transmits 100 packets, and the packet interval is 1 second. And a cyclic transmission mode is adopted, namely, the directional transmission is carried out on the first receiving terminal, then the directional transmission is carried out on the second receiving terminal, finally the directional transmission is carried out on the third receiving terminal, and the like.

The number of the receiving ends is 3, the receiving end wireless module antenna adopts an external sucker antenna and is provided with an SMA inner pin interface, and the height of the antenna is 17 cm. Because 433M wireless signals are received, the antenna connected with the receiving end can be indoors, and the communication speed of the MCU and the serial port of the wireless module is 9600 bps. Air rate 2400bps, channel 17, receiving end address: 9991,9992,9993, three receiving ends are set, four digit nixie tube is designed at the receiving end to display the counter of the received packet, the counter represents the number of packets received by the receiving end in a certain distance and decoded correctly.

In urban multi-building areas, the packet loss rate is less than 1% when indoor reception is carried out within 5 km-6 km, in open areas, no building shelters exist, signals are accurately received by the original module within a test distance of 8000m, and no packet loss exists within 5 km-6 km in an actual test. If automatic relay is adopted, the receiving end counter displays that the packet loss rate is less than 3% about 10 km. Compared with the traditional FSK, the LoRa spread spectrum greatly improves the penetration capability, can realize large power and long distance, and has strong anti-interference capability.

The transmitting end and the receiving end can transmit and receive correctly only under the conditions of consistent transmitting and receiving frequency, air baud rate, radio frequency rate and the like. Even if the illegal transmitting end can transmit through the parameters, because the data packet is carried out in the MCU of the transmitting end and the AES128 is adopted in the data packet head for encryption, the illegal transmitting information is discarded by the receiving end because the data head cannot be decrypted. Thereby ensuring that the data is not illegally interfered. For example: in an experiment, a transmitting end can be set to be broadcast-type transmission, namely, a receiving end address is set to be 0xFFFF in the MCU, so that three receiving ends all receive signals, but illegal data are discarded because the data head cannot be decrypted.

In a multi-building environment, 6km distance, 1 transmitting terminal and 3 receiving terminals, transmitting time and date information obtained by decoding the GPS in an idle state, displaying the time and date information on the 7-inch color screen of the receiving terminal, and operating the device after several months of experiment.

Embodiments of the present invention are illustrated in fig. 1a, 1b, 2, 3 and 4. A433 MHz broadcast type message communication device is provided, which comprises a transmitting terminal and a plurality of receiving terminals.

The transmitting end consists of a PC end, a transmitting end MCU, a 433MHz serial port wireless transmitter, a GPS receiver, a 4G/GPRS interface and special transmitting software running on the PC end.

And the PC end is connected to the transmitting end MCU through an RS485 interface bus. And sending the message to be sent to the transmitting end MCU in a serial port mode for processing. Because the transmitting end is installed outdoors, a hub is generally used, for example, a 4-port RS485 interface hub with lightning protection and photoelectric isolation is adopted.

The transmitting end MCU adopts STC15W4K32S4, and is used for receiving the packaged data packet message sent by the PC, receiving the GPS message and decoding, and receiving the message sent by the mobile phone through the 4G/GPRS interface, the transmitting end MCU packages the data packet by the flow method shown in figure 2, and the packaged data packet is transmitted to the 433MHz serial port wireless transmitter for transmission.

The 433MHz serial port wireless transmitter is a remote data transmitting module based on a serial port, LORA spread spectrum transmission is carried out, the model is SX1278, the transmitting end MCU sets a speed of 9600bps, the power is 1W, the working voltage is +5V, 433MHz is selected from the working frequency of 410-441 MHz, and the aerial transmission speed is 2.5 Kbps. The point-to-point fixed point transmission mode and the broadcasting mode are combined, and the antenna is arranged. Under the open and non-relay mode, the transmission distance can reach 8000 m.

The GPS receiver is a receiver with an RS485 interface and can receive GPS and Beidou signals simultaneously. The core MCU is mainly timed, the timed information comprises a time field and a date field, and the time field and the date field are used as part of data load.

The 4G/GPRS interface is an interface module with serial port output based on a 4G mobile network, and can realize transparent transmission of signals. The purpose is to transmit the message (needing authorization) sent by the mobile phone to the core MCU through the serial port, and the core MCU encapsulates the message into a data packet according to the flow method shown in FIG. 2 and transmits the data packet to the 433MHz transmitter for transmission. In specific implementation, the model is USR-780-V2, which meets the requirement of the 4G/GPRS interface.

The special software run by the PC terminal is computer software which runs under Windows and is provided with a message sending interface. The software has the functions of selecting group sending and sending an appointed address, having the functions of selecting an emergency message and a common message, having the functions of responding or not, encrypting or not and the like, and finally transmitting data to the MCU of the sending end, adopts Delphi7.0 software for development, is connected with a Microsoft SQL Server2005 database, and has the functions of inquiring, deleting, counting, modifying and the like.

As an example of implementation in the transmitting end: the constructed packet is shown in fig. 3.

The receiving terminal comprises a 433MHz serial port wireless receiving terminal, a 7-inch color screen, an MCU with STC15W as a core and an alarm unit.

The 433MHz serial port wireless receiving end has the same frequency as the transmitting end, such as 433MHz (410-441 is optional), the same channel, such as number 17 channel (0-31 is optional), the same air transmission rate, such as 2.5Kbps, and can statically configure the parameters thereof and dynamically configure the parameters thereof during operation.

The receiving end adopts a 7-inch color screen with a serial port. Obviously, there should be some difference between indoor environment use and outdoor environment use such as office, and it is better to adopt more than 10 inches display screen outdoors. The color display screen has a basic application program environment, and characters or symbols are displayed at corresponding positions by the control units of the color display screen only by sending data to the control units of the color display screen through a serial port. Because the color screen itself must have a Chinese character library, which generally contains at least 6763 Chinese characters, when encoding Chinese characters, only 1 Chinese character is encoded into a Chinese character internal code of 2 bytes, thus greatly reducing the transmission amount of data in the air.

Referring to fig. 4, the receiving end receives data and the transmitter package in reverse. And decoding the data of each field from the defined data packet.

The method for preventing the program file from being illegally rewritten is as follows: downloading password protection, wherein the running programs of the MCU at the transmitting end and the receiving end cannot be rewritten without a password.

Frequency range of 433MHz wireless communication module transmission: 410 Mhz-441 MHz, every 1MHz a frequency band, total 32 frequency bands, adopting wireless data transmission radio station without relay broadcast can reach 8000 m. In order to avoid the illegal interference of the same frequency band 433MHz, the same channel, such as number 17, and the same address, such as (9999) data, the method adopted is as follows: in the data portion of the custom message protocol, a 5-byte header is defined, for example: "MNPQR". Even if the frequency, channel, and reception address are known, the illegal data is discarded because the decryption key cannot be obtained and the correct data header cannot be obtained. Thereby avoiding data interference.

The above description is only a preferred embodiment of the present invention, and the scope of the present invention is not limited thereto, and any simple modifications or equivalent substitutions of the technical solutions that can be obviously obtained by those skilled in the art within the technical scope of the present invention are within the scope of the present invention.

Claims

1. A broadcast message communication device based on 433MHz, characterized in that: the MCU module packages data by using a self-defined protocol method and then transmits the data to the transmitting end wireless communication module for transmitting; the MCU program memory is encrypted by hardware, and the secret key is encrypted by an AES128 algorithm; the receiving end adopts multi-address coding, and decodes the message by using an encryption key stored by the receiving end MCU, and the message can be issued point to point or one to many; the maximum length of the transmitted message is 255 bytes, and the transmitting end and the receiving end adopt the same protocol method to carry out data communication; the format is as follows: a receiving end address 2B, a transmitting end address 2B, a data length 2B, an emergency feature 1B, a response feature 1B, an encryption feature 1B, a CRC 162B, a data header 5B, a date and time 12B, and a payload part nB encrypted by an AES 128-bit algorithm.

2. The 433 MHz-based broadcast messaging device of claim 1, wherein: the wireless communication module adopts a 433M data transmitter with extremely low power consumption, small volume and high reliability; serial communication, self-adaptive air speed, 8000m minimum transmitting distance and 1W minimum power.

3. The 433 MHz-based broadcast messaging device of claim 1, wherein: and the receiving ends of the multiple addresses split and process the received data based on the MCU of the receiving ends and output the messages to a 7-inch color LCD with a Chinese character library based on a serial port for display.

4. The 433 MHz-based broadcast messaging device of claim 1, wherein: the receiving end of the plurality of addresses has the function of responding the message to the transmitting end through the key.

5. The 433 MHz-based broadcast messaging device of claim 1, wherein: the MCU adopted by the transmitting end and the receiving end is an STC15W4K32S4 single chip microcomputer; at the transmitting end, a serial port 1 of the MCU is connected with a PC through an RS485 interface, a serial port 2 is connected with a 433MHz wireless communication module through a serial port, and a serial port 3 is connected with a GPS module through an RS485 interface; at a receiving end, a serial port 1 of the MCU of the receiving end is directly connected with the 433MHz wireless communication module, a serial port 2 is directly connected with a 7-inch serial port color screen, and an alarm signal is output to an alarm unit through a P1.0 interface.

6. The 433 MHz-based broadcast messaging device of claim 1, wherein: the data part sent by the transmitting terminal encapsulates the date and time information obtained by GPS decoding, so that the receiving terminal can receive the time and date information sent by the transmitting terminal indoors and is convenient to display on a specific terminal.