Fire alarm systems in commercial, industrial and large residential buildings can be fairly complex. Most of the fire alarm systems on the Cornell University campus are microprocessor controlled. The microprocessor will control the system for a particular building or part of a building, and report data back to a centralized computer. In Cornell's case, the centralized computer system reports data to Cornell's Environmental Health and Safety, as well as to the Cornell Police dispatch center.
We tried to design a fire alarm system which was much like the large systems discussed above. An Atmel Mega32 microcontroller was used. The system is capable of eight different zones. Each zone reports a zone alarm, or a zone trouble back to the microcontroller.
The maximum number of devices possible in the system is completely independent of the MCU programming. There are a maximum of eight different zones. Each zone is limited in the number of detection devices (smoke/heat detectors, flow detectors, pull stations) only by the zone circuitry. The system is customizable, so that zones can be enabled or disabled; all eight zones do not have to be in use at all times.
If at any time a device in the zone, or the zone itself becomes disconnected, or has another problem, a trouble condition is detected. This is reported to the VT100 terminal. As an extra failsafe, the time is reported to the VT100 terminal and always running. If the time ever stops being reported at the terminal, that would symbolize that the system has been disconnected from the terminal, or that another problem has occurred. An alarm is also reported to the VT100 terminal. The system can be set so that an alarm can be silenced so that the audible and visual alarms in the building do not go off upon an alarm. An alarm can also be triggered manually via the user interface.
The user can program customizable names for either the system and/or the zones. Additionally, the system can be password protected. The system password, customized names, as well as zone enable information, is stored in nonvolatile memory so that if the power is disconnected, settings will be saved.