Brief Description
(Abstract)
of Sentinel Project
CE 150 - Computer Interfacing
back to CE150
A prototype computer-interfaced security system was developed with detectors for smoke, presence and motion. A personal identification number (PIN) keypad activated lock and dialer were also developed. The whole system is interfaced via parallel port and is controlled by a custom supervisor program.
The presence detector uses a laser beam with timer delay receiver to selectively detects objects that cut the laser beam. The clock frequency to the time is varied to enable to select the size of an object that may trigger the detector. The motion detector employs an array of infrared transceiver-receiver circuits. Motion is detected by the sequential triggerring of any of the sensors on the array. The smoke-detector works by comparing the light intensities detected by two light-dependent resistors (LDR) sharing the same light source. One LDR, the reference, is in a confined environment while the other is open to interference such as smoke which will vary the light intensity on that LDR.
The PIN keypad is a grid of switches, which the columns receive signals from an active system and the columns send signals back to the system, the combination of row-column corresponds to a certain key on the pad. Decoding of hte circuit is done via a software module within the supervisor program. The lock, on the other hand is activated by driving a DC motor to push a barrel bolt into a socket which locks the door. The opening of the lock is achieved by applying a reverse DC voltage to the motor.
A supervisor program, written in C and runs on DOS controls the whole. The program continually polls the system which sends signals to a multiplexer to determine which device from which to read triggering signals. If-then statements within the program also determine what consequences the system should undertake in case one of the detectors are triggered.
One major consequence taken by the system is to dial a phone number via a modem connected to any regular phone. A number of phone numbers may be configured to correspond to various authorities which will be called by certain triggers. Other consequences include turning off the presence and motion detectors (when a person enters a correct PIN and enters the guarded system), unlocking the door in case of fire when there are people inside, etc.
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