A low cost DIY wireless security system enables a homeowner to install the system without running cables around their house. It consists of a mains-powered (and battery-backed-up) control panel with a simple keypad, built-in sounder, LCD output display, and voice dialler. Battery powered wireless PIR sensors and a wireless alarm siren are also included in the package.
When the system is first installed (and at any future change), the homeowner can configure the system via its control panel. This configuration process involves 3 stages - pairing devices, assigning an emergency contact number, and setting a secret PIN:
1. The homeowner "pairs" all of the wireless sensors and alarm siren with the control panel, assigning each a zone number and optional description text. The user selects pairing mode, and then selects either a zone number, or the wireless siren. If they select a zone number, they can (optionally) enter additional descriptive text via the keypad, and then confirm. The pair operation then begins.
For each pair operation/zone number, the control panel broadcasts a pair request on the sensor frequency for 60 seconds.
The user then presses the "pair" button on the appropriate sensor or siren the user wants to assign, which causes the device to respond to the "pair" broadcast and identify itself to the control panel. If no devices respond in the 60 seconds, the panel returns to configuration mode.
If a device is successfully paired, the panel stores this zone data (number and description) along with a unique key for each device in onboard non-volatile memory. This allows the control panel to communicate securely with each peripheral individually by sending and receiving data as follows:
2. The homeowner can then enter an emergency contact number, which is also stored in the panel's onboard non-volatile memory.
3. Finally, the homeowner must programme a secret PIN which is used to arm and disarm the system. This is also stored in the panel's onboard non-volatile memory.
The PIR sensors, once paired, only transmit in the following circumstances to save power, and are otherwise idle:
1. If they detect motion, they send the encrypted data key to the control panel identifying themselves and a special code to indicate they have detected motion.
2. If they detect their batteries are running low, they send the unique encryption key and a special code to indicate the low battery state.
When the system is operating, its normal state is idle/disarmed. The panel display shows "Ready". During idle mode, the control panel will only display a different message if it receives a battery low message from a sensor. This message will identify the zone number (and description if available) with the low battery status. It will also "chirp" its internal sounder once every 5 minutes to alert the user. The user can acknowledge this alert with the keypad, which will stop the regular chirping.
When the user enters their secret PIN, they are prompted to confirm that they wish to arm the system. If they do, the system enters armed mode. The control panel displays "Armed". During armed mode, if the system receives a PIR motion message, it will enter alarm mode.
During alarm mode, it will display "ALARM!" on its LCD, sound its built-in sounder and will instruct the wireless siren to sound by sending it an encrypted "alarm sound" signal.
The wireless siren will sound for 15 minutes and then automatically silence itself, unless it receives an encrypted "alarm stop" signal from the panel in the meantime - in which case it will stop sounding immediately.
If the system continues in alarm mode for 90 seconds without being disarmed, the panel dials the stored emergency number and plays an automated message. If the connection fails (e.g. line busy, no dialtone), the number is redialled every 20 seconds until a connection is made (or the alarm is cancelled)
During alarm mode, if the secret PIN is entered, the system disarms and displays zone information about the zone that caused the alarm on the panel. It then returns to idle mode.
Apply the Requirements and Architecture Models to perform the analysis and design of the alarm control software described above (you can make - and should document
- necessary assumptions), and document all results obtained from each of the following tasks:
(1) Define the data and control context diagrams of the alarm control firmware.
(2) Define data flow diagram DFD 0 which shows at least four different processes, and its corresponding control flow diagram CFD 0.
(3) Define process and control specifications based on DFD 0 and CFD 0 produced in (2); the latter including any timing specification deemed necessary.
(4) Enhance the diagram DFD 0 produced in (2).
(5) Define architecture flow diagram AFD 0.
(6) Define the traceability matrix.