Home security system is needed for occupants' convenience and safety. In this paper, we present the design and implementation of a low cost, low power consumption, and GSM/GPRS (Global System for Mobile Communication /General Packet Radio Service) based wireless home security system. The system is a wireless home network which contains a GSM/GPRS gateway and three kinds of wireless security sensor nodes that are door security nodes, infrared security nodes and fire alarm nodes. The nodes are easy installing. The system can response rapidly to alarm incidents and has a friendly user interface including a LCD (Liquid Crystal Display) and a capacitive sensor keyboard. The wireless communication protocol between the gateway and the nodes is also suitable
for other home appliances. Furthermore, some methods are taken to ensure the security of system information.
There is a growing interest in intelligent home network as a way to offer a comfortable, convenient and safe environment for occupants . In order to enhance the occupants convenience and safety, home security system is indispensable in the field of intelligent home network. According to connecting mode, home network can be divided into two kinds: wireless network and non-wireless network. The wireless technology has some remarkable benefits comparing with non-wireless technology. For example, it makes the installation and maintenance easier and reduces the system cost. Bluetooth, ZigBee 802.11 and wireless USB are the most popular technologies in the field of home wireless network.
How to inform user in real time when alarm incidents occur has become a crucial feature of home security system. This can be done via internet or GSM/GPRS. GSM/GPRS is more convenient than internet. The main reason is that the GSM/GPRS network has wide spread coverage making the whole system available for almost all the time. Furthermore, GSM/GPRS network has high security infrastructure which makes sure that the information sent or received cannot be monitored.
In this paper, a low cost GSM/GPRS based wireless home security system is presented. The system includes two parts: wireless security sensor nodes and a GSM/GPRS gateway. It has the following features:
(1) Low cost. All the microprocessors used in the sensor nodes and the gateway are cheap 8-bit microprocessors, and all other devices are inexpensive.
(2) Low power consumption. All security sensor nodes are powered by batteries.
(3) Easy installing. Because the nodes communicate with the gateway by wireless, they can be installed anywhere inside the home.
(4) Rapid response. The GSM/GPRS gateway will send SMS (Short Message Service) messages to inform remote PMP (Property Management Person) and users
when alarm incidents occur.
(5) Friendly user interface. The system has a friendly user interface including sixteen capacitive sensor keys and a LCD. Users can view the states of security sensor nodes, modify password of the gateway and change the mobile phone number for receiving the alarm messages.
(6) Emergency alarm function. There is an emergency alarm key (SOS key) in the GSM/GPRS gateway which makes users at home to alarm in emergency situations.
(7) Information security method. In order to ensure the security of system information, some security methods are taken, such as a password for gateway to prevent unauthorized person to access the system, and a pseudo security key for data encryption and decryption to ensure security wireless communication.
The general structure of the home security system is shown in Fig. 1. The system includes two parts: wireless security sensor nodes and a GSM/GPRS gateway. There are three kinds of sensor nodes in this system: door security nodes, infrared security nodes and fire alarm nodes. The GSM/GPRS module is the interface between the gateway and the GSM/GPRS network.
The general diagram of wireless security sensor nodes is shown in Fig. 2. Every sensor node has a wireless transceiver module and a microprocessor. The microprocessor receives and analyses the sensors' signals to detect the state of node.
Fig:2 . The general diagram of sensor nodes
The infrared security node adopts a pyroelectric infrared sensor (PIR). PIR sensor responds to the infrared radiation of human body whose radiation is strongest at wavelength between 9.4 Î¼m and 10.4 Î¼m . The sensor can be placed in the entrances of rooms or other areas. When an intruder enters these areas, the sensor will detect the infrared radiation generated by the intruder and output a signal whose range is about 1mV and frequency is about 1Hz, as shown in Fig. 3.
Fig 3: Output signal of PIR sensor
The Fire Alarm Node:There are many fire-detection techniques. The common methods are based on temperature sampling, relative humidity sampling, smoke analysis, in addition to ultraviolet and infrared sampling. In this system, each fire alarm node adopts a temperature sensor and an infrared receiver. The temperature sensor monitors environment temperature and infrared receiver monitors heat and flames. If temperature or infrared of environment exceed defined thresholds, the node sends out alarm signal. The home security system discussed above has two kinds of alarms: abnormal alarms issued from three sensor nodes and emergency alarm started by users when they touch "SOS" key. Table I presents messages on LCD and SMS messages sent to user when alarms take place.
The flowchart of the menu subprogram is as follows
(1) Check up password.
(2) If the password is right, the menu appears on LCD, otherwise the sub program ends at once.
(3) Press 1 to 4 corresponds to the four functions of the menu: 1 for initializing password and the SOS number, 2 for changing password, 3 for changing the SOS number and 4 for quit.
"Menu" key should be touched in order to use functions of menu. User is requested to enter password firstly. If the input password is correct, the system menu will show on the LCD.
Press "1", the system password is changed to "222333"and mobile phone number for help is changed to"00000000000".
(2) Change password
Press "2", the system requests user to enter new password. When completed, the system asks user to input again to verify. If two inputs are same, the password will be changed to the new one. During the process, you can use "Cancel" key to delete what you have entered.
(3) Change mobile number
Press "3", the system displays the existing mobile number and prompts user to enter new number. When finish inputting mobile phone number, press "Set" key to complete the amendment.
Press "4", the system quits the menu.
This paper presents the design and the implementation of a wireless home security system. PSoC devices and wireless transceiver modules are adopted. The system has a friendly user interface and employs some methods to reduce the power consumption. Communication of the system is complete wireless, which makes the system easy to install and use. The system is low cost, low power consumption and easily operable. In addition, the wireless transceiver modules enable the system to transfer other information such as voice and picture rather than just alarm signals. As a result, the system can lightly be expanded to other applications.