Intelligent anti-theft alarm system hardware circuit overall solution

The traditional wired burglar alarms only detect alarms when there is pilferage, and there are no controllers inside, so they are easily damaged, and installation and expansion are inconvenient. The wireless anti-theft alarm designed in this paper is controlled by a single-chip microcomputer and has powerful functions and can be easily extended to a multi-purpose smart home system.

1 system hardware circuit 1.1 overall structure Intelligent alarm system hardware overall, including the central controller, transmitter and receiver module, DTMF (dual-tone multi-frequency) module, voice module, telephone interface module.

1.2 The central controller selects AT89C51 one-chip computer, the circuit is shown as in Fig. 2. P3.2 (INT0) is connected to an anti-theft detector to detect theft. If an eavesdropping occurs, external interrupt 0 is triggered. P2.1 connects the voice circuit to achieve voice playback control. P2.3 connects the telephone interface chip, realizes the simulation to pick up and hang up the control. P1.0 output analog remote control. P1.4 connection alarm buzzer. P0.0-P0.3 are connected with MT8888 D0-D3 respectively and used as data bus. P2.0 is connected to RS0 of MT8888 and controls the selection of MT8888 internal registers. P2.8 and MT8888 CS control MT8888 strobe. P3.3 (INT1) connects to pin 24 of the telephone interface chip to detect ringing. P3.6 and P3.7 are connected to WR and RD of MT8888, respectively, to control the reading and writing operations of MT8888.

1.3 detectors and wireless transmitter, receiver circuit detector selection of wireless magnetic door, from a permanent magnet and door magnetic body (with a normally open type internal reed switch) two parts. Wireless transmitter circuit is included in the main body of the door, and the receiving part is a super-regeneration module circuit. PT2262/PT2272 composes and decodes the chip pair. When the permanent magnet leaves the reed pipe for a certain distance, the detector immediately transmits a 315 MHz high-frequency radio signal containing the address code and its own identification code (data code). The receiving circuit judges whether it is the same by identifying the address code of this radio signal. Alarm system, then according to its own identification code, determine which detector is the alarm.

1.4 DTMF Transceiver Circuit The alarm circuit shares a telephone line with the subscriber's telephone. Select MT8888 DTMF transceiver, combined with single-chip microcomputer and voice circuit, to achieve a variety of telephone signal tone detection, automatic dialing; or decoding remote telephone button signals, transmitted to the microcontroller, to achieve remote control.

1.5 The voice circuit uses ISD1420 as the basic recording and playback circuit. All the address lines are set to 0 and the playback start address is 0. When the S3 key is held down, recording starts and data is stored starting from address 0 until the memory is full or the key is released. When the S1 key is pressed, playback starts.

1.6 Telephone interface circuit DTMF transceiver circuit, voice circuit need to be connected to the outside world through the telephone interface circuit, use PH8809 phone interface chip.

2 System software 2.1 Main program flow system The system controls through the one-chip computer, start a buzzer circuit at the time when there is stolen, at the same time dial the pre-set telephone call automatically; Or accept and control long-rangely.

2.2 Phone Alarm Subroutine Flow The detection subroutine is used to obtain the echo signal after the phone is lifted to obtain a count value. The determination subroutine determines that the detected echo is a dial tone, a busy tone, and a ring back tone according to the standard of the program control switch. The dialing subroutine dials the pre-set phone under dialing conditions. If the other party is busy or no one answers after the ringing, it delays for a while and waits for the next round of dialing. The sounding subroutine plays back the pre-recorded alarm sound after the dialed call is connected.

2.3 The remote control subroutine flow did not happen. When the caller called back, he detected ringing. When several ringings were set, nobody answered the call. The system automatically connected the phone and waited for the user to enter the phone through the keyboard. Commands are sent to the host via DTMF and various remote control actions are performed after decoding.

3 Conclusion The intelligent anti-theft alarm system features complete, easy installation and easy application. Switching to other sensors, such as fire, temperature, and smoke detectors, can be used as a fire alarm system. In addition, by extending the number of external memory, host probe interface, display module, voice circuit, etc., the system can make the system more intelligent and more powerful.