My Part for Technical Proposal

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.