4.0 Proposed Solution
Our
team would like to further improve the overcrowding situation in school by
implementing a wireless sensor network (WSN) system to detect the number of
tables taken in each individual canteen, and display the number of tables
available on the television screens around the campus. This proposed solution
aims to disperse the crowd to the various canteens, and to reduce waiting time
for a table. The system is inspired by the Parking Guidance System (PSG) which
is widely used in commercial and office buildings across Singapore. We will be
explaining further about how a PGS works for better understanding of our
proposed solution.
4.1
Parking Guidance System (PGS)
A typical
PGS will allow drivers to know the available parking lots at the different
levels of a multi-storey carpark. An overview of the lots available is shown on
LED boards at the main entrance of the carpark, and other strategic locations
such as at the different zones. The main purpose of this system is to reduce
time wasted looking for a lot, ease traffic congestion, save fuel consumption,
and prevent drivers from being frustrated. It is an effective system, and
numerous shopping malls, office buildings, and others are currently utilising
the PGS.
Figure 5: Sample PGS by Singapore
Technologies
The
hardware and their features in the above figure include:
·
Master
controller
·
Zone
controller
·
Ultrasonic
proximity sensor
·
Vehicle
detection bar
·
Main
and directional display
Ultrasonic
proximity sensors are installed above each parking lot. These sensors produce
sound waves and waits for the reflected energy to bounce back. When a car
enters the lot, it changes the amount of energy reflected, and the presence of the
car will be detected. The lot indicator light will then change from green to
red, showing that the lot is taken. A signal will be sent to the zone
controller which computes the lots available in the zone and sends the
information to the directional displays around the carpark. The same signal is
also sent to the master controller which collects and collates all the
information, and disseminates it to the main display and supervisory system.
The main display will be updated with the available number of lots left. The
vehicle detection bar basically detects the number of cars entering a
particular zone.
4.2
Types Proximity Sensors
Proximity
sensors are commonly used for detection without physical contact. In general,
proximity sensor converts the information on the presence or movement of an
object into an electrical signal. Here, we will discuss about three different
types of proximity sensors and their applications.
Table
1: Comparison of the different types of proximity sensors.
|
|
Detects
|
Characteristics
|
Cost/Unit*
|
|
Passive
Infrared (PIR) Sensors
|
Change in heat
|
Since
measures the change in heat of the sensing area, it is prone to false
detection as it is sensitive to temperature change by the environment.
Advantages:
·
Able
to differentiate the chair from human.
·
Affordable
Disadvantages:
·
Tables
near the doors of the canteen may receive false detection due the temperature
difference between the air outside and inside of the canteen.
|
S$10 - S$15
|
|
Infrared (IR)
Sensors
|
Presence of an
object
|
The sensor
uses a LED that emits IR light that it is able to detect. When an object is
present, the IR light will bounce back and the light sensor will detect it.
It can also detect brightness.
Advantages:
·
Affordable.
Disadvantages:
·
Unable
to differentiate the chair from human.
|
S$15 - S$20
|
|
Ultrasonic Sensors
|
Presence of an object
|
This sensor uses a
vibrating device which emits ultrasonic waves. When the ultrasonic waves hit
an object or surface, it will bounce back to the sensor. The sensor will be
able to determine the distance between the sensor and the object/surface
based on the time travelled by the waves.
Advantages:
·
Able
differentiate the chair and presence of human using the difference in
distance detected.
Disadvantages:
·
Costly.
|
S$25 - S$60
|
*Prices are based on sgbotic.com, a leading
supplier for sensor tools in Singapore.
From Table 1, our team decided to
utilise the PIR sensors for our system as it is the most affordable type of
sensor. In addition, it is able to detect human temperature which is suitable
for our system.
4.3
How It Works
Our
proposed solution will require some modifications on the actual PGS to meet the
needs of the target audience (i.e. users of the canteens). Based on the
comparison of the different proximity sensors, we decided to utilise the PIR
sensors for our system. The main reason why we chose this particular type of
sensor is because of its ability to differentiate between a chair and the
presence of human. On top of that, the PIR is the most cost effective motion
sensor as seen on the table above. The figure below shows an overview of our
system.
Figure 6: System of proposed solution
The
system requires installation of one PIR sensor under each table. There will be
a sensor controller in each of the canteen which will collect data of the
number of tables occupied. The information will then be transmitted to the
master controller, where all the information will be collated and evaluated.
The number of available tables left in each canteen will be shown on the
television screens located at lobby of the different buildings. The general
flow of the system is as follow:
1. Student sits at a table in
Canteen 4.
2. PIR detects the presence of a
human.
3. Sends this signal to the
sensor controller.
4. Sensor controller will
transmit the information to master controller.
5. Master controller will
evaluate the information received.
6. Information will be sent to
the TV screens.
7. Updates number of tables left
on TV screens.
