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Based on the embedded GPRS and digital wireless alarm system

In Electronic Infomation Category: B | on April 13,2011

Abstract: In order to achieve the security situation on the home environment in the event of real-time monitoring and IDT72V3690L15PF datasheet and alarm can automatically dial when the voice prompts or send alarm SMS, GPRS and IDT72V3690L15PF price and design of a digital wireless technology based on the embedded telephone alarm system. The system SoC (system on chip) C8501F020 MCU core for control and IDT72V3690L15PF suppliers and processing, and use 2. 4 GHz digital wireless transmission technology to connect sensors, receiving the sensor signal acquisition, to monitor the surrounding environment. Meanwhile, the system combines GPRS SMS and fixed telephone network, to achieve a reliable alarm transmission and remote control. Systems also designed the terminal interface, the system can be easily set a password or user preset alarm phone number, and to generate and query system alarm log.

Intelligent home alarm system as an integral part of daily life are playing an increasingly important role. Alarm systems are commonly used today by the fixed telephone network transmission SCM police intelligence, stability and reliability are relatively low, and human-computer interaction difficult, complex operation, which directly affect its application in real life value, so alarm system is urgently needed improvements in design and optimization, in order to promote its development.

This paper, a microcontroller for the control of the enhanced core, combined with sensor technology, digital wireless technology, GSM mobile communication network, fixed telephone network, embedded technology and intelligent computer control alarm system. Relative to the previous alarm system, the system to GPRS SMS alarm to make up for the shortcomings of fixed phones in function and performance have been strengthened and improved to enhance the stability and reliability, and improved human-computer interaction interface, simplifying the user management system operation.

1 System Overview

The system as a system with enhanced MCU processor and improve system stability and reliability of the work to minimize false positive and false negative rate of the system. System through the gas, smoke, door magnet, infrared, ultrasonic multi-sensor collaborative work environment for real-time monitoring of the security situation, combined with the fixed telephone network and the GSM network, to achieve fire, Pirates of the emergency situation and various voice Alarm and SMS tips. The system also provides users with easy-to-computer terminal interface, reducing user management and setting of the operating complexity. In addition, the system also has alarm log, the user password through the system and verify the terminal interface option date to see the day after the success of the system alarm logs, to a certain extent, to achieve the alarm evidence. System, there are six specific functions:

(1) digital wireless technology and sensing technologies, real-time monitoring security situation in the family environment;

(2) the central controller receives the alarm signal, automatically through the fixed telephone network for voice dial preset alarm phone numbers or send text messages through GPRS communication module prompts;

(3) with automatic pick and DT MF decoding machine, the user can call a remote control system, such as: pre-alarm, alarm monitoring lifting systems;

(4) through the system terminal or system keyboard interface to set or change passwords, or modify the preset phone numbers;

(5) record and check the alarm log;

(6) disconnection detection function automatically detects the system to the telephone network connection exception.

2 system design and implementation The system MCU C8051F020

minimum system as the core control circuit, reducing the electromagnetic radiation on single chip digital radio road caused by the interference and increase system stability. Sensor group and the digital wireless transceiver module environmental control circuit, monitoring of environmental security. GPRS communication module and DT MF DTMF decoding circuit system the alarm information transmission channel. GPRS communication module through the GSM network to send text messages to mobile phones, transmission alarm information. DT MF DTMF decoding circuit through the fixed telephone network for automatic dialing and remote control. Telephone interface circuit including disconnection detection circuit, ringing detection circuit, automatic pick electromechanical Road, to achieve break detection, ring detection, automatic picking. Voice circuit is used to store the alarm sound and playback controls. Figure 1 is a block diagram of overall system design.

overall system design block diagram in Figure 1

2. 1 system hardware design

The system consists of five hardware modules: digital wireless transceiver circuit, GPRS interface circuit, DTMF dual tone multi-frequency coding and decoding circuit, telephone interface circuits, voice circuits.

2. 1. 1 digital wireless transceiver circuit NRF24L01

system uses the core 2. 4 GHz half-duplex digital wireless transmission module. nRF24L01 has six control signal lines, SPI bus, four pins: CSN (SPI Enable), SCK (SPI clock), MOSI (Master Out Slave In) and MISO (Master In Slave Out); IRQ for the received data interrupt signals generated for the SCM query; CE for the chip select signal is set low then open the data transmission module. MCU through the SPI serial bus to configure the internal registers and nRF24L01 send and receive data.

Connected with the sensor wireless transmitter circuit, the alarm is triggered the event control node nRF24L01 MCU digital wireless transmission module transmitting the node address and the collected alarm signal; in the wireless receiver circuit, C8051F020 communicate directly with the nRF24L01, receiving sensor node address and alarm information to determine the alarm by identifying the type of node address.

2. 1. 2 GPRS module interface circuit

The central processor receives the sensor sends the alarm signal, the control GPRS communication module, through the GSM network, mobile terminal users to send text messages to the alarm.

MCU control circuit and GPRS communication module connected through the UART interfaces. However, the GPRS module signal line for the 12 V S232 level, the microcontroller level is 3. 3 V, it must be carried out MAX3232 level conversion. When the alarm, the microcontroller through the serial port to control instructions and content of messages sent to the GPRS communication module; GPRS communication module identified control command, according to the content of messages to send text messages to the user.

2. 1. 3 DTMF dual tone multi-frequency coding and decoding circuit

DT MF DTMF decoding circuit mainly constituted by the MT 8888, including the DTMF encoding circuit, DTMF decoder circuit and ring identification circuit. Coding circuit for automatic dialing, remote control instruction decoding circuit identification. Ring circuit can correctly identify the dial tone, busy tone, ring back tone identification.

Automatic dialing, the microcontroller will send data to the called number is sent to register, synthetic DTMF signal, amplified by transmission through the telephone interface to a PBX telephone network, to achieve dial-up. Remote control, remote DT MF control signals through the high and low frequency filter filter, then through the digital encoder, the corresponding control instruction binary encoding, stored in the receive data register, while the MT 8888 to generate an interrupt signal IRQ port ; microcontroller interrupt, the read data in receive data register, identification control instruction. Ring tones identify when, 450 Hz sinusoidal ring signal from the DTMF IN port input, through a center frequency of 450 Hz, 250 Hz bandwidth filter, if the signal falls within the passband, the output of the same IRQ port frequency square wave.

2. 1. 4 telephone interface circuit

Telephone interface circuits including automatic pick electromechanical Road, ringing detection circuit and the disconnection detection circuit. Abstract Electrical and Mechanical Road

automatically pick up the analog automatic, when the dial-up alarm or remote control, the system automatically pick up, access to telephone networks. The remote control, ringing detection circuit to a telephone ring signal can be detected, thereby automatically hook. Mainly by the ring detection circuit and high-speed optocoupler 6N138 constitute LM393 voltage comparator. Agreement under the program-controlled switchboards, AC ringing signal is 25 Hz, 90 V sine wave. Ring signal through the DC isolation capacitor and the limited pressure resistance, the drive optocoupler optocoupler output logic pulse is generated, after shaping the voltage comparator, got a square wave pulse. Pulse signal input SCM, SCM can count pulses, namely, to a certain number of pulses, the automatic hook. When the system is not properly connected to the telephone network, the disconnection detection circuit can automatically detect the failure and prompt.

2. 1. 5 voice circuit

System uses as a voice recorder ISD1760 chip. Microcontroller through the SPI serial bus connected with the ISD1760, transmission SPI command, configure the internal registers and for voice recording. ISD1700 as a SPI slave, almost all of the key operation can be achieved through the SPI command.

Some SPI commands: such as PLAY, REC, ERASE, FWD, RESET, GLOBAL_ERA SE operation similar to the corresponding independent key operation, the other SET_REC, SET _PLAY, SET _ERASE command allows the user to specify the recording, playback and erase start and end address.

System initialization settings, you should first of all based on the length of a variety of tone, with a good distribution of the corresponding look-up table method of starting and ending address of the memory. And by the hardware to provide users with audio interface and control interface. Dial-up alarm, the alarm type according to the corresponding address and plays a tone.

2. 2 system software design

2. 2. 1 system, the main program

System power, the first delay of 100 ms, the microcontroller and the peripheral circuits have sufficient time to reset. In the system initialization process, to enable the external interrupt C8051F020 6, 7, and serial port interrupt, and reset all interrupt request flag. External Interrupt 6 handles remote control, external interrupt 7 processing alarm, PC serial port interrupt handling control commands. Interrupt flag bit scan cycle separate ways, if the interrupt request flag is set, then transferred to the appropriate interrupt service routine. Figure 2.

main program flow chart of Figure 2 system

2. 2. 2 alarm subroutine

When the alarm, call the hook hook function for the simulation, and the ring test. Microcontroller counter ring detection time T 0 4 s, the counter T 1 Dui MT 8888 IRQ output square wave to 4 s count. According to PBX protocol, ring tones, the signal for the error + 25 H z to 450 Hz continuous sine wave, is continuous dial tone, busy tone to 0. 35 s pass, 0. 35 s off, back to the ring for the 1 s-pass, 4 s off. Threshold can be set to count, according to the different counts for ring tones recognition. For example, dial tone the upper and lower threshold count (450 +25) * 4 = 1900 and (450 - 25) * 4 = 1 700. Figure 3.

alarm subroutine flow chart in Figure 3

2. 2. 3 remote control subroutine

With the remote control when the corresponding external interrupt 6 interrupt request flag is set, the system subroutine from the main program into the remote control. First of all, MT8888 set to DT MF mode, and then decode the remote password, the password to compare with the local, if not match, then hang up; or authentication passed. Authenticated, MT8888 remote control instruction decoder and passed to the microcontroller. Microcontroller instruction execution under the control of the corresponding control operation, the implementation is complete, automatically hang up.

2. 3 system terminal interface

System terminal interface shown in Figure 4.

Figure 4 System terminal interface

When the system is in standby mode, the security indicator light; when in alarm state, the corresponding alarm status indicator will flash indicating the alarm status. Change the password to enter the original password, to prevent others from illegal tampering, thereby enhancing the security of the system; change numbers also need to enter a password, or can not be modified. Query system log to enter the password; select a date, double date to check the days police log. Alarm logs can be stored in text file format and can change the store directory for easy viewing and call later.

3 Results languages ??

The system uses the companys enhanced U.S. Silabs 8-bit MCU C8051F020 as the core of the system reduces electromagnetic radiation interference digital wireless transceiver circuit; used to 2. 4 GHz frequency is the carrier frequency of the public digital wireless transceiver circuit, Compared with the traditional 433 MHz and 315 MHz wireless transceiver circuit has a strong anti-interference ability, firing distance, and the advantages of small circuit; and combined multi-node sensor group, the security situation in real-time monitoring of family, and timely information about security risks . Meanwhile, on the basis of the fixed telephone network to increase the GPRS SMS alarm function, make up the fixed telephone network to pass through the alarm function on the lack of information, improve system security. Also designed a desktop personal computer terminal, to improve the human-machine interface more user-set / change the password, preset / edit phone numbers, check the alarm log and so on. The experiment proved that the system is low cost, stable, functional and friendly man-machine interface features, has a strong practical research significance and social value, and broad market prospects.

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