According to its principle, whenever a magnetic field is applied in a direction perpendicular to the flow of electric current in a conductor, a potential difference is induced. This voltage can thus be used to detect whether the sensor is in the proximity of a magnet or not. The Arduino can

detect this voltage change through its interrupt pin and determine whether the magnet is near the sensor or not.

Fig 2H: Hall effect without the presence of magnetic field

Hall effect with the presence of magnetic field 2.7. LCD:

In today’s world it is important to keep track of what is happening within the machinery,be it automated or semi automated machine. By having a clear picture of the result of the functioning,we can easily come to certain conclusions. Hence, LCD plays a very significant role in the transparency of the process.

Liquid Crystal Display screen is a 16x2 display element which is frequently used to display information. It can display 32 characters. It is a flatpanel display which uses the light-modulating properties of liquid crystals. We know that Liquid crystals do not emit light directly.

LCD displays are gradually replacing seven segment displays because of a myriad of advantages, such as:

1. LCDs are cost effective and reasonable.

2. They can be easily programmed.

3. Special characters can be made, these are called customized characters which can be again easily displayed.

4. Animations can be created.

5. Interfacing with any microcontrollers.

Fig 2I: LCD

LCD displays utilizes two layers of polarizing material with a liquid crystal solution between them. When an electric current is passed through the liquid, this results in the crystals to synchronise, this is done to isolate light from the medium. Therefore, each crystal is like a shutter window which sometime allows light energy to pass through and sometimes acts like a blocking wall. This is the basic and rudimentary functioning of a LCD. Monochrome LCD images usually appear as dark gray or blue images, this is covered by a top layered grayish background.

Types of LCD:

Color LCD displays use two basic techniques for producing color: Passive matrix is considered the comparatively the less expensive of the two technologies mentioned. The other technology which is also called thin film transistor or active matrix produces more bright and intense colour images that are sharp and of high resolution. These are also called the traditional CRT displays but the only drawback to this technique of LCD is that it very expensive. Recently,to give competition to the more used active-matrix LCD, recently passive matrix started utilizing a new CSTN and DSTN technologies. This was done to produce sharp colours rivaling active matrix.

PASSIVE DISPLAY: Passive displays are widely used with segmented digits such as calculators, fax machines and remote controls, most of which are monochrome or have only a few colours.

ACTIVE DISPLAY:These are used in desktop computer monitors and LCD TVs. 99.99% of all laptops, active displays are essentially called “active matrix”.

Characterstics of LCD:

When we say 16x2, we mean that there are 16 characters in one line and 2 represents 2 lines in our display.

6. N.v optional for +3V power supply in a LCD.

There are various positives of using a LCD.The screen of LCD is very energy efficient. Due to its low electrical power consumption lets us sue it as a battery powered equipment and this thus more efficient than a CRT. Since its an electronically modulated optical device made up of infinite number of segments which are controlling a layer of liquid crystals and arranged in front of a source of light or a reflector, which helps to produce images in color or monochrome. Liquid crystals were first discovered in 1888. By 2008, annual sales of televisions with LCD screens exceeded sales of CRT units worldwide. CRT became absolutely obsolete for any daily purpose used in appliances because of the popularity of LCD.

Each pixel OD an LCD typically consists of a layer of molecules aligned between two transparent electrodes, and two polarizing filters, the axes of transmission of which are perpendicular to each other. With no actuall liquid crystal between the polarizing filters, light passing through the first filter would be blocked by the second one.

The surface of the electrode that are in contact with the liquid crystal material are given so as to align the molecules in a certain direction or orientation. This kind of treatment consists of a thin polymer coat that is unidirectional and it is rubbed also in a unidirectional way. In LCD, electrodes are made up of transparent conductor called Indium. This leads us to conclusion that LCD is an intrinsic passice electronic device and its also a simple easy light valve which opens and shuts the amount of light passing which is governed by LCD drivers.

Before applying an electric field, the orientation of the LCD molecules are determined by the alignment at the surfaces of the electrode. If the applied voltage is large enough, the liquid

crystals molecules in the centre of the layer are almost completely not twisted and the polarization of the incident light is not rotated as it passes through the liquid crystal layer.

Table 2.1: LCD pins

2.8. VOLTAGE REGULATOR 7805:

Voltage regulator 7805 is a well known member of the 78xx series of fixed linear voltage regulators. There are times when there is a not a proper voltage output because of voltage fluctuations from the input. This is when we need the voltage regulator. It does what it so needed a system,to able to control the voltage output. Hence, in our project we are using voltage regulator to maintain the fixed and constant voltage value at the output. In the well known series of 78xx, xx represents the value of fixed voltage it is designed to provide. This is how we know that while using 7805, +5V regulated power supply is used. One or more capacitor is/are used to be connected at the input and output pins, though it depends on the voltage levels at both the ends- input and output.

Fig 2J: PIN DESCRIPTION OF VOLTAGE REGULATOR:

Pin 1: Input voltage – name given to it is “input” and the voltage varies from the range of 5V TO 12V.

Pin2: Ground- name given to this pin is ground in the regulator and its value is 0V.

Pin3:Regulated output: 5V is the exact butit also ranges from 4.8V to 5.2V. designated as a the output pin in the regulator.

78xx series:

Here is the list of the commonly used positive voltage regulators. These are called positive voltage regulators as they are positive with respect to the ground. 7805 has a 5volt output. 7812 produces 12volts. Similarly, 79xx ICs can be used to give a negative supply voltage. If we combine both, 78xx and 79xx, we get a positive and negative supply voltages.

Fig 2K: Pin out of LM7805

2.9. POTENTIOMETER:

A potentiometer is informally called pot. It is three terminal resistor within which there is sliding or rather a rotating contact that makes an adjustable voltage divider. When we use only two terminals of the resistor, it turns into a rheostat which is basically a variable resistor.

Potentiometer is generally used to measure the potential and is also called a voltage divider.

Fig 2L: potentiometer

In document MAJOR REPORT Final (Main Content)- Arduino Based Bag Security System (Page 26-34)