23-08-2014, 09:45 AM
Design and Implementation of an Embedded Surveillance System by Use of Multiple Ultrasonic Sensors Project Report
Design and Implementation.pdf (Size: 415.77 KB / Downloads: 18)
Abstract
In this paper we design and implement a surveillance
system based on an embedded system with multiple ultrasonic
sensor modules to enhance the system’s reliability. The ultrasonic
sensor module includes a transmitter and a receiver, and they are
placed in a line direction. Because the ultrasonic air transmission
will spread a beam angle, we use multiple ultrasonic receivers to
receive the ultrasonic transmission. If any intruder passes
through the ultrasonic sensing area, the ultrasonic transmission
will be blocked by a human body. As the receivers will not
receive any ultrasonic transmission produced by the ultrasonic
transmitter, the system will sense when someone has passed
through the surveillance area. We use a Majority Voting
Mechanism (MVM) for a group of sensors. If over half the
sensors in a sensor group sense a signal blocking, then the
majority voting circuit will send a trigger signal to the
surveillance system.
INTRODUCTION
Recently, the use of a surveillance system detect images is
becoming more important. Although the embedded
surveillance system is frequently used in the home, office or
factory [1], this configuration requires a high performance
core, which works against some advantages of embedded
systems, such as low power consumption and low cost. Other
researchers construct an external signal to trigger the
embedded surveillance system by means of a PIR sensor,
which is triggered when an intruder enters the monitoring area
[2]. However, a PIR sensor has a high miss rate when the
intruder walks at a slow speed. Hence, to solve this problem,
we use ultrasonic sensors to implement an embedded
surveillance system. In addition, as using a single receiver to
receive the ultrasonic transmissions can be influenced by
refraction and reflection, to enhance the reliability of the
system, we use several sensors to receive the ultrasonic
transmissions.
SYSTEM ARCHITECTURE
Fig. 2 shows our design which uses the embedded board as
the system core. We separate the transmitter and receiver byplacing them on opposite sides. When an intruder enters the
transmission direction, the human body will block any
ultrasonic transmission. If the receivers do not receive the
ultrasonic transmission, the embedded surveillance system
will use the MVM to count the sensing states of all ultrasonic
sensors. If, because of the result, the MVM is used, the Web
camera immediately begins to capture the images of the
intruder. After capturing the images, the embedded
surveillance system will upload these captured images to the
Web page through the Internet. The users can then watch the
images on either a PC or a PDA by connecting to the Interne
Software modules
The program of the majority voting mechanism contains a
detection of the GPIO function, a counting and majority vote
function, an image captured function and a Web server, as
shown in Fig. 3. The embedded system always scans the GPIO
sockets, all of which are connected to ultrasonic receivers. To
verify the state of each ultrasonic receiver, the embedded
system determines the voltage levels of the GPIO sockets.
When the system reads 5V from a GPIO socket, we know the
ultrasonic receivers, which have been blocked, will execute
the majority voting program by counting the state of each
ultrasonic receiver. The majority vote is achieved by the
sensor groups of the different GPIO sockets, and the result
determines whether to adopt the majority voting mechanism or
not. If the result is not to adopt the majority voting
mechanism, we know that the ultrasonic receivers have
probably been blocked because of refraction and reflection.
The embedded system then returns to the initial state, scanning
the GPIO sockets. If, as a result, the majority voting
mechanism is adopted, we know that the ultrasonic receivers
have been blocked by an intruder. The embedded system
interrupts the detection procedure and starts the Web camera
which then begins to capture images. When the procedure of
capturing images is finished, the embedded system starts the
detection procedure over again. If the intruder is still in the
monitoring area, the count of the GPIO sockets’ voltage levels
will continue to use the majority voting mechanism, and the
embedded system will start the Web camera again to capture
images
Hardware modules
We design an ultrasonic transmitter and receiver. The
transducer will transform the voltage waveform into ultrasonic
transmissions to be transmitted in the air. The receiver sensor
will transform the ultrasonic transmissions into the correct
voltage waveform. We use an amplifier to enlarge the voltage
waveform and the filter will filter any frequency with the
exception of the 40 KHz frequency. As the result we will
know after the comparator determines the level of the voltage
whether the ultrasonic transmission has been blocked or not
IMPLEMENTATION RESULTS
For this design we observe and measure the operation of the
single sensor and multiple sensors with 2 m, 4 m, 6 m, 8 m
and 10 m separately. TABLE I shows the primary results of
our experiments
CONCLUSIONS
Our experiment shows that the overall sensing probability
improves with the use of multiple sensors that have the
majority voting mechanism. However, the result is a higher
cost for the use of multiple sensors, amplifier circuits and the
voting circuit.