Design of intelligent home security alarm system based on LPC2478

Overview

The intelligent alarm systems currently on the market have relatively simple performance and are expensive. Some systems often send out alarms to notify the owner or alarm center only when the doors and windows are damaged, and the response takes some time. The longer the time, the more dangerous it is to the property at home. The best way to ensure security is to send out a voice alarm when the criminals attempt to invade, increase their psychological pressure, and force them to leave automatically. When this method fails, you can also record the invasion time and send a short message to notify the owner or alarm center. This solution is based on this idea. When there is human activity outside the door, the signal detected by the pyroelectric infrared sensor is processed by a dedicated chip and sent to the main controller LPC2478 based on ARM7. The main controller sends a general prompt or warning prompt instruction based on the length of the signal time. At the same time, the warning information will be sent to the owner's mobile phone in the form of a short message so that the owner can call the police at the first time. This solution is highly intelligent and easy to use. It does not require the owner to perform complex operations and is very suitable for use by ordinary families.

System Principle

Before the system works, the householder first sets the best alarm response time through the keyboard according to the environment and flow of people in his home. When the whole system starts working, the pyroelectric infrared sensor RE200B will continuously collect infrared signals within the detection range. When a human body appears, a high level will be output to the main controller - LPC2478 based on ARM7 architecture after being processed by the signal processing chip BISS0001. When the duration of the high level is within the best alarm time, the system will issue a general voice prompt to the person outside the door, such as "Please press the doorbell"; when the best alarm time is exceeded, the system will issue a warning voice prompt, and start the SMS sending module to send alarm SMS to the householder's mobile phone. The level of the alarm SMS will be upgraded step by step according to the length of the best alarm time. The IIS audio bus interface provided by LPC2478 can be used as a codec interface to connect to an external 8/16-bit stereo audio codec chip - UDA1341TS, thereby realizing the voice alarm module of the system. The SMS sending module uses Siemens' TC35i module, which is controlled by the main controller to send alarm SMS through the GSM wireless network of the mobile operator. The system uses an external storage unit - SD card, which has large capacity, low price and is easy to use. The voice information of normal prompts and alarm prompts and the content of SMS are pre-stored in the card. Using LPC2478 as the main controller of the system can reduce the use of external chips, thereby reducing the size and power consumption.

Hardware

The hardware part of the home intelligent security alarm system mainly consists of five parts: alarm signal acquisition and processing module, main control module, voice alarm module, short message sending module and preset information storage module. The overall system block diagram is shown in Figure 1. The main control module controls the work of the other four modules to realize the functions of the system.

The main control module uses the microcontroller LPC2478 based on the ARM7TDMI-S core, which has a very high integration level. It has an embedded 98K on-chip static RAM and 512KB on-chip FLASH memory, and integrates ADC, DAC converter, watchdog, real-time clock RTC, 1 IIS audio interface, 3 IIC interfaces, 4 UART interfaces and other resources. It is convenient to expand the IIS interface and JTAG debugging interface, with few external expansion chips and ultra-small LQFP208 package. The whole system is miniaturized and the circuit is simple, which reduces the development and production costs. The chip can achieve a maximum operating frequency of 72MHz, has strong functions, and can meet the requirements of the embedded system mC/OS-II.

The alarm signal acquisition and processing module is mainly composed of the pyroelectric infrared sensor (PIR) RE200B and the infrared sensor dedicated processing chip BISS0001. The pyroelectric infrared sensor uses the pyroelectric effect to detect the infrared radiation of the human body in a non-contact form and convert it into a voltage signal. In actual use, a Fresnel lens is installed in front of the sensor to increase the detection distance to more than 10m. In view of the characteristics of slow change and small amplitude of the PIR signal, the BISS0001 infrared signal dedicated chip is selected. The chip integrates an operational amplifier, a voltage comparator, a state controller, a delay timer and a blocking time timer, which fully meets the needs of infrared signal processing. The D, G, and S terminals of RE200B are the power supply terminal, the ground terminal, and the target output voltage terminal respectively. The output signal VO of the BISS0001 chip is sent to the main controller for reading. The specific circuit is shown in Figure 2.

The voice alarm module is mainly composed of an audio codec chip UDA1341TS produced by NXP that supports the IIS bus data format. IIS is a standard interface jointly launched by SONY and NXP and other companies mainly for digital audio processing technology and equipment. It separates audio data and clock signals, thereby avoiding the jitter problem caused by the clock, and the system no longer needs a device to eliminate jitter. The IIS bus interface signal lines of UDA1341TS are: bit clock input BCK, word selection input WS, data input DATAI, data output DATAO and audio system clock SYSCLK signal line. The main controller LPC2478 provides two groups of six signal lines for sending and receiving the IIS bus interface, namely IISRX_CLK, IISRX_WS, IISRX_SDA, IISTX_CLK, IISTX_WS, IISTX_SDA. The specific circuit is shown in Figure 3.

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The short message sending module is composed of Siemens' TC35i module. The TC35i module is mainly composed of six parts: GSM baseband processor, GSM radio module, power supply module (ASIC), flash memory, ZIF connector, and antenna structure. In order to facilitate debugging, we purchased a GSM module development device based on TC35i. The development device has reserved wiring ports for connecting to the main controller, namely TXD, RXD, and GND. Just connect these three wiring ports to the RXD, TXD, and GND of LPC2478 respectively, and the module can be controlled by the main controller. The hardware connection is very simple, which can speed up the development progress.

The preset information storage module is mainly composed of SD card. LPC2478 provides SD/MMC card host controller, so when designing SD/MMC card interface circuit, you only need to connect these interfaces to SD/MMC card holder accordingly. The SD/MMC interface circuit is shown in Figure 4. SD card has two working modes, namely SD and SPI mode. In this design, we choose SPI mode. The SPI channel of SD card consists of the following 4 signals: CS (chip select), CLK (clock), DataIn (data signal from host to card) and DataOut (data signal from card to host). CS is the chip select signal line of SD card. During the whole SPI operation process, it must be kept at low level. CLK is convenient for synchronization. DataIn not only transmits data, but also sends commands. Similarly, DataOut not only sends data but also transmits response signals. SD card is mainly used to store normal voice and alarm voice information as well as preset alarm short messages. The whole operation is controlled by LPC2478.

System programming

This system is programmed using C language and is entirely modular in design.

Conclusion

The ordinary household intelligent security alarm system introduced in this article adopts the highly integrated LPC2478 microprocessor of NXP Semiconductors. The chip integrates IIS interface for voice processing, SPI interface for SD card information access, and UART interface for controlling the GSM module. The rich on-chip resources of this chip greatly meet the design requirements and simplify the peripheral circuits.