A multi-channel wireless anti-theft alarm system based on telephone network

With the continuous improvement of people's living and production levels and the strengthening of property safety awareness, people's demand for anti-theft alarms in homes, warehouses and other places is increasing. Traditional alarms have certain limitations. For example, they can only sound alarms locally, cannot notify the owner or community security, and cannot identify the theft area, and their functions are limited; the detectors use wired methods to transmit signals or power supply, which is inconvenient to install. To this end, this paper uses wireless radio frequency and telephone network communication technology to realize an anti-theft alarm system with multiple detectors, wireless connection, ability to identify theft areas, automatic dialing of preset telephone alarms and easy to use, and gives a detailed design scheme of the main software and hardware of the system.

1 Overall design
The system consists of multiple detectors and a host. As shown in Figure 1. The detector consists of a pyroelectric infrared detection module and a coded wireless transmission module. The detector detects intruders through the pyroelectric infrared detection module, and sends the position code to the host through the wireless module after detecting the intruder. The host includes a single-chip controller, a wireless receiving module, a voice module, a telephone module, an LCD display and buttons, and can be installed in a fixed position. The host receives the position code signal emitted by the detector through the wireless receiving module to identify the theft area. After receiving the theft information, the host calls the preset phone through the telephone network. After the call is connected, it plays the pre-recorded alarm voice information such as the resident's address, the theft area, etc. to complete the alarm. The user can preset the alarm phone number and record the alarm voice through the host's human-machine interface, and can also perform disarming and arming control.

2 System Hardware Design
2.1 Detector and Wireless Receiver Module
The circuit of the detector and wireless receiver module is shown in Figure 2. The pyroelectric infrared sensor D203S absorbs the infrared rays emitted by the intruder's body and converts them into electrical signals, which are output from pin 2 to the infrared sensor signal processor BISS0001. BISS0001 contains a 2-stage operational amplifier, a bidirectional amplitude detector, a delay timer and a state controller. The infrared sensor signal is first amplified by the 2-stage operational amplifier, and then the bidirectional amplitude detector generates a trigger pulse to trigger the delay timer to work. The state controller makes the output Vo (pin 2) output a high level within the delay time. When Vo is high, Q1 is turned on, and current flows between pins 1 and 10 of the relay module ATQ209, so that pins 7 and 8 are attracted and turned on. Pin 7 obtains the 9 V battery voltage and supplies the power supply terminal 5 of the wireless transmitter module, so that it can be powered on. Pins 1-4 of the wireless transmitter module are data input terminals. The input data is configured through jumpers JP1-JP4 as the bit code of the detector. The wireless transmitter module contains the coding modulation chip PT2262 and the 315 MHz high-frequency transmission circuit. When it is powered on, it modulates the position code into a high-frequency signal and then transmits it. The wireless receiver module contains the superheterodyne receiving circuit and the decoding chip PT2272, which can receive the high-frequency signal transmitted by the wireless transmitter module and demodulate the position code, and output it from pins 4-7.

2.2 Central Controller The 89C51
system uses the 89C51 microcontroller as the host central controller. The circuit is shown in Figure 3. Port P0 is connected to the data bus, which is used to transmit data between the microcontroller and the LCD, telephone module, and keyboard. Data transmission is carried out in time-sharing. P1.0-P1.3 are connected to the keyboard (Figure 4) to generate keyboard scanning signals. P1.4-P1.7 are connected to the data end of the wireless receiving module (Figure 2) to read the detector position code. P2.0-P2.2 are connected to the read-write control pins of the LCD (Figure 4), and P2.3-P2.6 are connected to the read-write control pins of the DTMF transceiver chip MT8880 (Figure 6) in the telephone module. P2.7 is connected to the telephone interface module PH8810 (Figure 7) to realize the control of picking up and hanging up the phone. P3.4 is connected to the IRQ/CP pin of MT8880 to detect the signal tone during the telephone call. P3.5-P3.7 are connected to the serial interface of the voice chip ISD4002 (Figure 5) to realize the operation of the voice chip by the microcontroller.

2.3 LCD and key module
The LCD interface and key circuit are shown in Figure 4. The system uses the SMC1602A standard character LCD display module, which can display 2 lines of 16 characters. The keys are in the form of a 4x4 matrix. The microcontroller inputs key scan signals from KEY-DB0 to KEY-DB4 and reads key scan values ​​from DB4-DB7. When no key scan is performed, KEY-DB0 to KEY-DB4 can be pulled to a high level by the pull-up resistors inside P1.0-P1.3. At this time, even if a key is pressed, it does not affect the data on the bus DB4-DB7.

2.4 Voice module
The voice module circuit is shown in Figure 5. The ISD4002 voice chip is selected to realize the recording and playback of alarm voice. The chip has a microcontroller serial interface and can record and play multiple voices. The voice information can be saved in the FLASH inside the chip when the power is off. In the figure, ISD-SS, ISD-SCLK, and ISD-MOSI are serial interface signals connected to the single-chip microcomputer. The single-chip microcomputer sends instructions through the serial interface to control the voice chip to work. When the voice chip works in recording mode, the voice is collected through the microphone and the internal circuit completes the recording and storage. When the voice chip works in playback mode, the voice is output from AUDOUT (pin 13), amplified by LM386M, and then output to the speaker and telephone interface module PH8810 (through signal AUDIO). The speaker is used to audition the recorded voice, and PH8810 can output the voice to the telephone network to realize voice alarm.

2.5 Telephone module
The telephone module includes a DTMF transceiver circuit and a telephone interface circuit, as shown in Figures 6 and 7. MT8880 is a DTMF transceiver chip used to generate dual audio signals and detect telephone signal tones. MT8880 has a single-chip microcomputer interface, and its operation is controlled by the single-chip microcomputer. In Figure 6, pins 14-17 are data pins, and pins 9-12 are read-write control pins. When MT8880 works in dual audio mode, it receives the telephone number transmitted by the single-chip microcomputer and generates a dual audio signal of the number, which is output from DTMFOUT to the telephone interface module PH8810 to achieve dialing. When MT8880 works in call processing mode, it shapes the telephone signal tone input from DTMFIN into a square wave and outputs it from IRQ/CP (pin 13) to the single-chip microcomputer. The single-chip microcomputer counts the square wave to determine the dial tone, ringback tone, and busy tone to achieve the detection of telephone signal tones.
The telephone interface circuit is implemented using the telephone interface module PH8810. In Figure 7, pins 2 and 3 are used to connect the telephone line, and pin 4 is connected to the microcontroller for on-hook and off-hook control. The dual audio signal and alarm voice signal of the dialed number are input to PH8810 from pins 29 and 28. PH8810 automatically amplifies the signal and outputs it to the telephone line. The signal tone on the telephone line is extracted by PH8810 and output to MT8880 from pin 10.

3 System software design
3.1 Main program flow
The main program flow of the microcontroller is shown in Figure 8. The main program first displays the three main menu options of alarm voice recording and playback, telephone number setting, and arming and disarming control on the LCD, and then performs key scanning. If a selection key is pressed, the corresponding function code is executed according to the selection, and the main menu is redisplayed after the execution is completed. If no selection key is pressed, it is determined whether to arm. If it is armed, the anti-theft alarm program is executed.

3.2 Anti-theft alarm program flow
The anti-theft alarm program flow is shown in Figure 9. The program first queries the wireless receiving module for the detector position code data. If the data is zero, it means that no theft has occurred. Otherwise, it means that a detector has detected theft. If there is a theft, record the theft position code, set the theft occurrence flag, and then control PH8810 to perform the off-hook operation. After picking up the phone, set MT8880 to call processing mode to detect the dial tone. If a 450Hz continuous square wave signal is detected within 1s, it is judged that there is a dial tone. If there is a dial tone, set MT8880 to dual audio mode and send it a phone number for dialing. After dialing is completed, reset MT8880 to call processing mode to detect the ringback tone. If a 450Hz square wave signal is detected for 4s without and 1s with, it means there is a ringback tone. After detecting the ringback tone, if no signal tone is detected, it means that the other party has successfully picked up the phone, and the voice chip is controlled to play the alarm voice. After the playback is completed, clear the theft flag to avoid repeated alarms. If there is no dial tone or the other party fails to pick up the phone, the PH8810 will be controlled to perform the on-hook operation. Because the theft flag is not cleared, the program will still try to alarm the next time it is executed until it succeeds.

4 Conclusion
The multi-channel wireless anti-theft alarm system includes multiple wireless probes, which can flexibly record the required alarm voice, set multiple alarm phone numbers, control the arming and disarming functions, and has a liquid crystal display interface. It can identify the theft area and automatically call the preset phone number to alarm. The system has been applied to the actual home and factory warehouse anti-theft. The actual application shows that the system has the characteristics of easy installation, flexible and practical functions, stability and reliability, and meets the design requirements.