31-12-2009, 07:28 AM
MICRO CONTROLLER BASED SECURITY SYSTEM USING SONAR- A Project report
Abstract:
The problem facing many institutions like museums and banks is that of security
round the clock. Security guards are expensive and burglars have learned to evade
conventional security devices like infrared beams, thermal sensors etc. The use of
SONAR in a security system, as used in our project, is a novel idea, and as far as we
could determine, extremely difficult, if not impossible, to evade.
The infrared beams have the disadvantages of covering just a limited area in a room
and to cover a whole room requires many of these beams. This makes this
technology very expensive. It is also by no means foolproof and can be evaded by
experts as has been so ably demonstrated in so many Hollywood films. Temperature
sensors can also be evaded as they can either be made extremely sensitive and risk
false tripping of the alarm due to changes in ambient temperature or made less
sensitive at the risk of allowing evasion.
The use of SONAR offers us many advantages. It is nearly foolproof, albeit it be at
the expense of being extremely sensitive to the point that the only way to avoid
tripping of the alarm is to make sure that the room it is covering is free from any
movements. In this project we have designed and developed a unique security system
that utilises the capabilities of microcontroller and a special purpose SONAR
module. It is also extremely cost-effective when compared to similar systems
currently in use.
The principle of operation
This project has got a SONAR module mounted on a stepper motor . As the stepper
motor rotates, SONAR module sends out ultrasonic waves and scans the area. So, if
this product is placed in the center of a room, it can scan the whole room and the
range of scanning depends on the SONAR module used. With a Polaroid 6500 series
sonar ranging module, the range is about 6" to 35ft.
The inspiration for the product was from the idea used in MTI RADAR. In MTI
RADAR, targets are determined by comparing the echo pulses obtained from
successive scanning. In this project we intend to use a SONAR module. This is a
Polaroid 6500 series SONAR ranging module. This SONAR module sends out
ultrasonic waves when initiated by a pulse at its input pin INIT, and when it
receives back the ECHO, the ECHO pin goes high. A single pin of a port of the
microcontroller can be used to initiate the SONAR. When the SONAR is initiated, a
counter is started in a register in the microcontroller. And once the reflected back
waves reach the transducer of the SONAR module the ECHO pin goes high. Now
this high pulse is inverted using a 7404 NOT gate and then apllied at the
INTO(negative edge-triggered) pin of the microcontroller. INTO is an interrupt pin.
So when a negative edge appears at the pin, the control of the microcontroller goes to
an interrupt subroutine located at 0003H. After executing the interrupt
subroutine(given in the code) the counter stops. Now, the content of the counter is
stored in a memory location. Then stepper motor is rotated by a step. Then again the
same process as described above is repeated. The value of the counter in this case is
stored in next memory location. Thus, when the stepper motor completes one
complete rotation , data(counter value) are stored in as many memory locations as
the number of steps taken by the stepper motor to complete one rotation. The
number of steps taken by the stepper motor depends on the angle the stepper motor
deflects for each steps. In usually available (in college labs) stepper motor, if the
angle of deflection is 1.8 degrees, then the number of steps taken =360/1.8 = 200
steps, and if it is 0.9 degrees, number of steps taken = 360/0.9 = 400 steps. In this
project, we used a deflection of 1.8 degrees, which can be programmed in the
microcontroller. The output pins of port 1- i.e., P1.0, P1.1, P1.2, P1.3 are used to
control the stepper motor(see ckt. Schematics).
Now as the stepper motor has completed one rotation . Now the stepper motor is
ready to rotate in the directions opposite to that of the previous rotation(this is to
avoid streching of the wire connections between the main PCB and the SONAR
module mounted on the stepper motor).Again SONAR is initiated, value of the
counter at the time ECHO pin goes HIGH is compared with the memory location
where the data for the same position of the stepper in the previous rotation stored. If
there is a difference in value of the memory location and the present counter value,
we can assume that an intruder has intruded in to that position scanned by the
SONAR.Now the pin P3.4 of the microcontroller goes HIGH and switches on the
FM transmitter and thus the buzzer in the FM receiver at the hands of the security
starts beeping signalling abouthe intrusion. If there is no difference between the
memory and counter values, stepper motor is further deflected by a step, then again
SONAR is initiated, counter is started and then stopped at HIGH on the ECHO pin,
then the value of counter is compared with the content of the corresponding memory
location for the same position of stepper during the previous rotation. And this
continues until an intrusion occurs. So, a suitable program for the above processes
have to be written in to the ROM of the microcontroller.
Complete report pdf download:
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