2. SYSTEM DESIGN
This chapter deals with the design of the GSM based Building Security System. This chapter includes the project requirements, block diagram of the project along with the explanation of each of the blocks, and a description of standards used in the project.
The project is required to build a system, which can act as a security device to prevent an unauthorized entry into a building. For this, each of the door of the building is attached with the security system designed in the project.
For the working of the system, the owner is required to have a mobile phone to control the access to the door. The unit attached to the door consists of another mobile phone which has the facility to receive and answer incoming calls. Whenever the owner wants to open the door, he/she can call the phone number of the unit attached to the door and can enter the password to open the door.
The mobile phone at the receiving section is connected to a DTMF Decoder IC to decode the DTMF code. A microcontroller is required to process the decoded DTMF code and to activate the motor and the solenoid latch once the authentication becomes successful.
The microcontroller is required to be loaded with the correct version of the program for its proper working. In addition, the whole circuit needs to be realized on a Printed Circuit Board for the reliable and proper working and easier installation of the system at the sites. The testing of the project modules should be done along with each stage, and a final system testing should be done at the end.
2.2 Block diagram
2.2.1 Block diagram description
The block diagram of the project is shown in figure 4. It consists of the Transmitting mobile phone, which can establish a wireless connection to the Receiving mobile phone. Here, Global System of Mobile Communication (GSM) technology is used in order to communicate between the mobile phones. The signals from the Receiving mobile phone are given to the DTMF decoder, and then fed to the Microcontroller for processing. After processing of the signals, the microcontroller provides the control signals to the motor driver block, which is fed to the DC motor for powering the door. Also, the signals from the microcontroller are provided to the Solenoid latch. The exit switch is a simple switch kept near to the door inside the building to exit the door. The exit door switch is connected to the microcontroller.
2.2.2 Transmitter mobile phone
The transmitter mobile phone should be a normal mobile handset with a SIM card which uses a 2G technology or higher for its operation, and can be used to make calls to another cell phone. The mobile phone should have a keypad to enter the digits and make a call to another mobile phone. The GSM technology is used in order to make the mobile communication possible. Alternatively, this could be any GSM device with a SIM card, such as a GSM module, which can make calls to a second mobile number, and which has a functionality to transmit the DTMF signals.
2.2.3 Receiver mobile phone
This is the front end of the receiving section, and accepts the calls from the transmitting mobile phone. The Receiving mobile phone is a normal mobile handset with a SIM card and which uses 2G technology or higher for its operation, and can accept calls from another mobile phone. This mobile phone is set in such a way that the calls coming to the phone gets automatically accepted after a delay of approximately 1 second. This phone should have a headset port which provides the audio output to be given to the DTMF Decoder IC.
2.2.4 GSM Technology
Figure 5: Architecture of GSM Mobile Network
GSM or Global System of Mobile Communication is a cellular phone technology which enables the mobile phone users to communicate over the mobile phone. GSM technology uses Time Division Multiple Access(TDMA) to achieve the addition of users into the network and it works in the 900MHz, 1800 MHz bands.
GSM consist of four main parts, which work together – The mobile phone handset, the BSS or Base Station Subsystem, the NSS or Network Switching Subsystem, and the OSS or Operation and Support Subsystem.
The Base Station Subsystem is used for handling of calls and its scheduling and is an intermediate between the mobile handset and the Network Switching Subsystem. The BTS or Base Transceiver Station connects to the mobile device, and the Base Station Controller or BSC controls the operation of several BTS.
The NSS is associated with the functions of switching and connection of calls to the right numbers after authentication. It also does the tracking of locations. It has the registers such as Home Location Register(HLR) and Visitor Location Register(VLR) to store the details of its users.
Regarding security of the GSM network, GSM is the most secure of all the telecommunication technologies, and it encrypts the voice calls using the A5/1 later upgraded to A5/2 and A5/3 standards, and also has an authentication for the SIM card in the mobile handset. It won’t accept a duplicate SIM card, and calls will only be allowed through a single SIM card. Moreover, with the coming of 3GPP and other technologies in the future, there will be more security features.