2.2 Component Architecture

The system comprises of two major components: Atmel AVR-based microcontroller coupled with either GSM modem or GSM mobile phone and a web server. The first component is installed directly at location to be guarded, preferrably masked or completely hidden. The microcontroller is then connected to up to four PIR detectors (or any other type of normally closed connectors, magnet-hermetically sealed pair for instance), main power and backup battery supply, optionally to external relays to control appliances like bulbs, heaters, fans. If mobile phone with embedded camera and Java Virtual Machine (JVM) is used then pictures will be taken automatically every time when controller inputs change states or timer goes off or SMS request to do so is received.

There are certain requirements for mobile phones to be used. First, mobile phone must have system connector with serial port wired on it. The serial port must be accessible from inside Java application running on that phone. Second, GPRS feature must be available on the phone. Third, in order to use full camera resolution, the procedure of taking photos must be done not through Java API but by means of so-called keypad emulation. It means that the microcontroller itself imitates key pressing and thus takes photos. When Java application code is launched, it is aware of newly taken pictures, so it receives additional textual data from microcontroller, combines them with binary streams representing new photos into HTTP request which is sent to web server via GPRS transport. In other words, fourth requirement is support of keypad emulation. There is another issue related to Java applet signing absence of which may result endless confirmations from mobile phone each time when COM port or GPRS connection is accessed. As the process of becomming certified developer and obtaining a certificate for Java applet sigining is relatively costly there are ways to overcome this obstacle for certain models of mobile phones. Current system was designed and tested with Siemens CX65/CX70 mobile phones but can be adapted and used with any type of mobile phone if it meets all the abovementioned requirements. If any particular model does not comply with them but has system connector and supports AT commands it is still possible to use it, but the system will work in simple mode when there is no necessity in web server, without option to take pictures and all notifications will be sent as SMS, not HTTP requests.

Optionally temperature sensor might be installed as well, in this case all taken pictures will have temperature measured at the moment of exposition. Location and orientation of mobile phone with embedded camera is chosen get a viewport of the area where one of the detectors is installed. It might capture a potential intruder when the detector triggers.

The second component, web server, is responsible for multithreaded processing of incoming requests from remote systems, storing data into a database, displaying stored results in a convenient way as dynamic web pages. Current implementation is based on MySQL database and set of PHP scripts but in fact due to its relatively simplicity might be port to JSP, Perl etc. It also might be easily intergated into already existing web solutions, web portals and so on. Current implementation supports standard PHP user authentification to prevent data to be viewed by unauthorised individuals.

The overall system's component layout in given below:

Figure 2.1. Overall Component layout

Overall Component layout