Solar Cell

The solar cell is a type of cell that transforms the light energy into electricity. The principle of solar cell is like photovoltaic action. This type of action occurs in all semiconductors, which are basically formed to absorb the light energies.

The basic solar cell consists of a P-type and an N-type semiconductor material (usually silicon or selenium), which consists of a PN joints/junction. The bottom layer is covered with a conducive contact's cover. The bottom layer is away from the light, i.e the light does not reach the bottom. Most of the upper surface area is open so that maximum light can fall and a small contact is placed on the top edge. The P-Type Surface layer is very thin (0.5mm) so that the light can reach the junction.

Although silicon is usually used to create solar cells. Apart from this, P-type junction is sometimes done by the type of p-type selenium. When the light is falling on the solar cell, then the PN nucleus of the solar cell is energized, the pair is formed in the electron hole, which is near the junction.Through the creation of positive and negative ions, an electric field is created near the PN junction, which develops a potential in the horizon of the junction. By the electric field many electron comes through the junction. If the intensity of light is increased, then the movement of carrier will carry more. The current flowing through the junction is proportional to the intensity of light.

Terminal voltage of cells is proportional to the intensity of direct light. Depending on external load, cell voltage may be up to a maximum of 0.6 volt. If many cells are arranged in an array, then more electric voltage can be achieved.When the cells are arranged in series or parallel, just like the battery works. If 10 cells are connected in series, each cell produces 0.5 volt in 150 mA, then the total will be 5 volt. Two parallel solar banks can provide 5 Volt at 300mA.

Solar Cell Uses:

• In Solar Energy Converter
• For the recharge of the battery of the board satellite
• Solar cells are used for driving
• Light measurements
• Light detection circuits.

DC Network

 1. Define electric current?

Ans: The valence electrons in different atoms of a material are free to move from one point to other. When an electron field is applied to a conductor the motion of electrons gets channelized. More electrons flow in one direction than in the other. The rate of flow of electrons is called current.

I= (dq/dt)

2. Define potential difference?

Ans: Absolute potential of a point is the work done in moving a unit positive charge from infinity to that point. The potential difference between two points is the work done in moving a unit positive charge from one point to the other. It measured in volts.

3. Define the word "Resistance"?

Ans: Electric current in a conductor consist of movement of electrons. When electrons flow through a material, they collide with other atomic particles and energy is lost in these collisions. The energy lost per unit charge is the voltage drop. The ratio of voltage drop to current is the resistance of material.

Uni-Junction Transistor (UJT)

A Uni-junction transistor (UJT) is a switching device.It switches from blocking to conducting state when the applied voltage reaches a critical value. It is a bar of high resistivity semiconductor with ohmic contacts at each end. The bar is usually of n-type material. A p-type emitter is alloyed at an intermediate position along the length. (In complementary UJTs the bar is p-type and the junction is n-type). When the junction is open or reverse biased, the resistance between base 1 and base 2 is a few kilo-ohms (fig. 1).

Fig: 1: The Symbol, Construction & Equivalent circuit of UJT 

When a positive voltage VBB is applied between B₂ and B₁ , the potential of point E will be ηVBB. The factor η is known as the intrinsic stand off ratio and depends on internal resistance R_B1 and R_B2 of the bar. If V_E is less than V_C , the p-n junction will be reverse biased, the emitter current will be negative and equal in magnitude to the small reverse saturation current. The V-I characteristics are shown in Fig. 2. When V_E = ηVBB + V_D ,where V_D is the forward voltage drop of the diode, the emitter base junction will become forward biased. The emitter current will become positive. The point A is known as peak point. The corresponding voltage and current are Vp and I_P respectively. The holes injected by the emitter drift towards B₁. Therefore, the number of charge carriers in the lower half region of the bar increases and the resistance R₁ decreases. Therefore, the potential of point C will decrease and the p-n junction will experience a higher forward bias. Therefore, the potential of point C will decrease and the p-n junction will experience a higher forward bias.

 Fig: 2: Characteristics Curve of UJT

Light Emitting Diode (LED)

Light energy can excite an electron into the conduction band. On the other band, when recombination takes place energy is released. In a semiconductor with an indirect band gap, e.g, silicon,germanium etc. recombination releases heat to the lattice. However, in some materials (e.g gallium arsenide), direct transitions occur between conduction band and transition band. In these materials, the radiation is in the visible and infrared regions. This effect, knows as injection electroluminescence, finds important application in digital watches, calculators etc. In a light emitting diode, an electric current causes the injection of minority carriers into regions of the crystal where they can recombine with majority carriers resulting in emission of light. The light output varies as (current)ⁿ , where n varies from 1.2 to 1.5 A wide range of photon energies extending from ultraviolet to infrared are available. The available energies can be increased still further by mixing the compounds. Commonly used displays are red, yellow,green and orange.
Figure-1 shows symbol for LED

Figure:01 LED Symbol

 Figure:02 LED circuit diagram

Figure-2 shows a simple circuit to regulate the current through an LED. The forward current I_f

 given by

I_f = (V-V_f  / R)

Where V_f is the forward voltages across the LED. The LEDs for different colours have different values of V_f and I_f. The diode D₁ is to protect the LED against reverse breakdown voltage. When reverse voltage exceeds a certain value, D₁ starts conducting and protect the LED.

Energy Levels

Energy Levels:
An atom consist of positively charged nucleus which contains almost all it's mass. Surrounding this nucleus are negatively charged electrons moving about in closed orbit. While in states corresponding to these discrete energies, electrons do not emit radiation and are said to be in stationary or non-radiating state. A stationary state is determined by the condition that the angular momentum of the electron in this state is quantized and must be an integral multiple of  h/2π,

Where,
            m= mass of electrons, Kg
             v= speed of electron in its circular path, m/s
              r= radius of orbit, m
             h= planck's constant
       
             n= integer
If n= 1,2,3,.................
We get stable orbits with radius r₁,r₂,r_3,................
For n-1, we get an orbit closest to the nucleus and possessing minimum energy. This lowest energy level is the innermost or K shell of the atom and can accommodate only 2 electrons.
The next higher energy level, known as L shell, can accommodate 8 electrons and so on.
The Outer orbit is generally not completely filled and the electrons in this orbit are known as Valence electrons.
In a transistor from one stationary state (corresponding to energy  W₂) to another stationary state (corresponding to energy  W₁) radiation is emitted.
The frequency of the radiant energy is__

Common Emitter (CE) Connection Of Transistor

The most transistor circuits operate with the emitter terminal as common to the input and output circuits. This is known as CE connection and is shown Figure-1. In this connection the left hand loop is the base loop and the right hand loop is the connection loop. The base circuit controls the collector circuit.

Figure:(01) CE  Connection of NPN Transistor

V_BB   is the base supply voltage and R_B is the current limiting resistance in base circuit. V_BE denote the voltage between the base and the emitter. V_BB is more than V_BE. Typically V_BB lies between 5 and 15 V in most circuits.
By changing V_BB and R_B. We can control the base current. The base current control the collector current. V_CC is the collector supply voltage and V_CE is the voltage between collector and emitter. R_C is the current limiting resistance in the collector circuit. As before the base emitter junction is forward biased whereas the base collector junction is reverse biased. The currents I_B, I_E, I_C are assumed positive when they flow into the transistor.

Figure-02 shows the output characteristics of the CE connection. These characteristics depict the relation between collector current I_C and collector to emitter voltage (V_CE) for different values of base current.
These characteristics are for a n-p-n transistor. These characteristics have three distinct region, i.e. active region, saturation region and breakdown region.

The active region is the region in which the curves are almost horizontal. V_CE is between a fraction of 1V and a few volts. In this region, the collector junction is reverse biased and the emitter junction is forward biased. When a transistor is used as an amplifier, it must operate in this region only. The base current is  I_B = - (I_C+I_E)

Basic Concepts of Amplifier CKT

Introduction:

The collective abbreviation of the two English words 'transfer' and 'resistor' is the transistor.

It basically works on the Resistance Transfer rule. The transistor is called a current driven device. And this current is transfer by resistance. That's why the name of the device is transfer resistor or transistor. Transistor is formed when connecting two Semi-conductor diodes as well. Transistor has three Regions (or Layers) and three terminals or electrodes or leads. The terminals are: collector, base and emitter.

Three scientists of America's Bell Telephone Laboratory invented transistor in 1948. There was a Revolution in the electronic world after the transistor was created.

Picture: John Bardeen, William Shockley and Walter Brattain at Bell Labs-1948

Transistor is the active device. Transistors are usually used for amplification and switching. Transistor has two PN Junctions. Every PN junction has a potential barrier.

Due to the barrier of the transistor, the input supply/signal is not transmitted instantly. As a result, the complete signal is not amplifiable; the part of the original signal is excluded. Particular part of the signal is a major drop in the gap between the faithful operations. To avoid this error and difficulty, the transistor has to be biased. This means that when crossing the signal through a transistor circuit, the circuits have to be biased to maintain the value of the zero signal collector current and collector emitter voltage.

Fig: PNP & NPN Transistor Symbol

Conditions of  biasing are: (1) Base emitter junction forward biasing and (2) Base collector Junction reverse biasing is done.

When the transistors send a small signal to the magnified size of the Output, then it is called amplification.The device is called Amplifier. So Transistor is one kind of Device that works as an amplifier & switching.

Amplifier:
The method in which the weak signal is changed into a strong signal, it is called amplification. The device that is used to amplify the amplification process is called an amplifier.

Bank Vault Security System with Password Protection (2nd Part)

Motor Driver Circuit (H-Bridge):

Two H-bridge motor driver circuits are used for driving the motors of the Door of the bank vault. One is used to rotate the door & another one is used to open/close the bolt of the door for locking purpose.

A PIC micro controller is used to operate the H-Bridges; it was programmed in a way that it sends

command to the H-Bridge to drive the motors clockwise or anti-clockwise for a certain period of time. The PIC micro controller gets it’s command from the Arduino Module after inserting correct or wrong password by the Keypad , if the password is accepted , then the Arduino sends signal to open the door

to the PIC micro controller, then the PIC micro controller drives the bolt motor clockwise for 2 seconds &

then the door rotation motor for another 4 seconds , when closing , after getting command from the Arduino it sends the command to the PIC micro controller , then the pic drives H-bridges in such a way that , the door rotation motor rotates in opposite direction for 4 seconds & then the bolt motor rotates in opposite direction for another 2 seconds & locks the door. The circuit diagram of a common H-Bridge is given below:

H-Bridge Circuit

Input Logic Table of the H-Bridge

Operating Principle of the System:

As it has been said before, it has 3 step security layer, first of all is password protection, a pre- programmed password can be saved & modified if necessary by the user, only authorized persons will know the password, after pressing the password on the keyboard, if the password is accepted, the door will open & will disable all the alarm systems, if the password is not accepted it will ring a warning sound & alert the user, if wrong password is inserted more than 3 times, it will secure the door & alert the law of enforcement team.

The second part of the security layer is physical interrupt alarm, a ‘Laser’ near to the door is aimed at a LDR sensor, if by any chance , anyone cut the bolts of the door or blow it away, the broken particle of the door or the door itself will cut the laser & will trigger the alarm.

The third part of the protection scheme is thermal security system, if anyone plans to get into the vault by breaking the vault floor or wall; the PIR sensor will detect the thermal movement & will alarm the trigger instantly. The second & third part of the protection scheme is only activated when the door is locked & de-activated when the door is unlocked.

Features of this system:

1. Full proof security system.

2. Can be monitored & controlled from distant main office wirelessly by Xbee module.

3. Triple layer security system.

4. Reliable & Durable.

5. Can be used as Home Security System or in Museum as well as Bank Vault.

6. Low power consumption, only 2.4mWatts.

7. No need to keep eye on surveillance continuously.

8. Alert sound & can call law enforcement team if necessary.

9. Battery Operated , can be backed up & also mains operated.

10. 24X7 online protection

11. Heavy duty vault door is controlled by geared motor

12. Auto locking & turning on the Alarm after shutting the vault door.

13. The password can be encrypted & the micro controller can be code protected.

14. Highly sensative thermal sensor for burglars.

15. Each PIR sensors can cover 10-45 meters.

16. More PIRs can be connected parallaly for larger space.

17. Physical interrupt system for blown door particle & man made interruption.

18. Low cost operating system using Arduino module[ATmega328] in C programming language.

19. Motor driver using PIC16F84A & two high current capacity H-bridge circuits.

20. Overall cost effective & parts are easily available on the market.

Programming the micro controllers:

Compiler: Arduino IDE, Micro controller: ATmega 238

#include "Keypad.h"

#include "LiquidCrystal.h"

const byte ROWS = 4;

const byte COLS = 4;

char keys[ROWS][COLS] =

{{'1','2','3','A'},

{'4','5','6','B'},

{'7','8','9','C'},

{'*','0','#','D'}};

byte rowPins[ROWS] = {

6, 7, A5, A4}; //connecting to the row pinouts of the keypad byte colPins[COLS] = {

A3, A2, A1, A0}; // connecting to the column pinouts of the keypad

Keypad keypad = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS );

char PIN[6]={'1','2','3','4','5','6'}; // The Password initially inserted in the program

char attempt[6]={0,0,0,0,0,0}; // used for comparison

int z=0;

LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

void setup()

{ lcd.begin(16, 2);

pinMode(A0, INPUT);

pinMode(A1, INPUT);

pinMode(A2, INPUT);

pinMode(A3, INPUT);

pinMode(A4, INPUT);

pinMode(A5, INPUT);

pinMode(6, INPUT);

pinMode(7, INPUT);

pinMode(8, OUTPUT);

pinMode(9, OUTPUT);

pinMode(10, OUTPUT);

incorrectPIN();

lcd.setCursor(0, 0);

lcd.print(" Press '*' & ");

lcd.setCursor(0, 1);

lcd.print(" Enter Password  "); }

void correctPIN() // do this if correct PIN entered

{ lcd.clear();

delay(1);

lcd.setCursor(0, 0);

lcd.print("The Password is: ");

lcd.setCursor(0, 1);

lcd.print("   Accepted   ");

delay(1000);

digitalWrite(8, LOW);

digitalWrite(9, HIGH);

digitalWrite(10, LOW);

lcd.clear();

delay(1);

lcd.setCursor(0, 0);

lcd.print("Security Sensors");

lcd.setCursor(0, 1);

lcd.print(" Are Disabled ");

delay(500);

digitalWrite(9,LOW);

delay(1500); lcd.clear();

lcd.setCursor(0, 0);

lcd.print(" Press '#' to  ");

lcd.setCursor(0, 1);

lcd.print("Enable Security");}

void incorrectPIN() // do this if incorrect PIN entered

{ lcd.clear();

lcd.setCursor(0, 0);

lcd.print(" The Password is ");

lcd.setCursor(0, 1);

lcd.print("  not Accepted     ");

digitalWrite(8, HIGH);

digitalWrite(9,LOW);

delay(500);

digitalWrite(8,LOW);

delay(1400);

lcd.clear();

lcd.setCursor(0, 0);

lcd.print("Security Sensors");

lcd.setCursor(0, 1);

lcd.print(" Are  Enabled ");

delay(2000);

digitalWrite(10, HIGH);

delay(1000);

lcd.clear();

lcd.setCursor(0, 0);

lcd.print(" Press '*' & ");

lcd.setCursor(0, 1);

lcd.print(" Enter Password "); }

void checkPIN()

{ int correct=0;

int incorrect=0;

for (int q=0; q<6 o:p="" q="">

{    if (attempt[q]==PIN[q])

{  correct++; }}

if (correct==6)

{ correctPIN(); }

else {incorrectPIN();

{incorrect++;}

if (incorrect==3)

{ lcd.clear();

lcd.setCursor(0, 0);

lcd.print("Warning!!!");

lcd.setCursor(0, 1);

lcd.print(" Alarm Enabled ");

}}

for (int zz=0; zz<6 attempt="" o:p="" wipe="" zz="">

{ attempt[zz]=0;  }}

void readKeypad()

{ char key = keypad.getKey();

if (key != NO_KEY)

{    switch(key)

{    case '*':

delay(10);

z=0;

break;

case '#':

delay(100); // for extra debounce

checkPIN();

break;

default:

attempt[z]=key; z++;    }}}

void loop()

{ readKeypad();}

Compiler: MikroC for PIC, Micro controller: PIC16F84A

void main()

{    TRISA=0b00000011;

TRISB=0b00000000;

while(1)

{      if(RA0_bit==1)

{ RB4_bit=1;

RB5_bit=0;

RB0_bit=1;

RB1_bit=0;

delay_ms(2000);

RB0_bit=0;

delay_ms(1000);

RB3_bit=1;

RB2_bit=0;

delay_ms(2000);

RB3_bit=0; }

else if(RA1_bit==1)

{     delay_ms(200);

RB5_bit=1;

RB4_bit=0;

RB2_bit=1;

RB3_bit=0;

delay_ms(2000);

RB2_bit=0;

delay_ms(1000);

RB1_bit=1;

RB0_bit=0;

delay_ms(2000);

RB1_bit=0; }

else

{ RB0_bit=0;

RB1_bit=0;

RB2_bit=0;

RB3_bit=0; }

}

}

Photo session:

Picture: The Arduino Module in the Project

Picture: Keypad & LCD interface

Picture: Door Controller H-Bridge & LDR Sensor Circuit

Picture: Circuit of the LDR Sensor & Buzzer

Picture: The bolted vault door

Picture: Complete Bank Vault Security Project

Picture: The Project was displayed in a Project Exhibition in AUST, Bangladesh

Picture: Team αlpha ( Ahsanullah University Of Science & Technology)

Bank Vault Security System with Password Protection (1st Part)

Background:

The main factor in bank vault is considered on the security system but most of the times it is based on human supportive surveillance system. But we know, that is not full proof & enough to give instant protection. My main purpose in this project is to give instant protection against any break-in & send alarm signal to the law enforcement team.

Introduction:

It has 3 step protection systems. The full system consists of a motherboard which contains the micro controller, keypad interface, display interface, motor controller interface & H-bridge circuitry with some input interface from the sensors. PIR (Passive Infra-Red) sensors are used for thermal movement detection & LDR (Light Dependent Resistor) sensors are used to detect unauthorized door movement. Each PIR can cover 10m-45m at an angle of ±15 degrees.

Materials:

This project is entirely based on the micro controller to ensure unbreakable system. The micro controller is code protected so that no one except the vendor / owner can override the system by changing password or anything else. I have used 2 micro controllers, one is ATmega328 & another is PIC16F84A, the first one was used to interface the keypad & a 16x2 LCD display & get input from the PIR & LDR sensors, the second one was used to drive the H-bridge for the operation of the automatic vault door.

Arduino Uno:

It's an open-source physical computing platform based on a simple microcontroller board consisting an ATmega328 micro controller, and a development environment for writing software for the board. Arduino can be used to develop interactive objects, taking inputs from a variety of switches or sensors, and controlling a variety of lights, motors, and other physical outputs. Arduino projects can be stand- alone, or they can be communicating with software running on your computer (e.g. Flash, Processing, MaxMSP.) 

Here is a picture of Arduino Uno:

Keypad (4x4 Matrix):

The keypad consists of 16 keys 0-9,*, # & A to D , it has 4 column line & 4 row lines , that is why it is called 4x4 matrix keypad. The keypad was connected to insert the password in the micro controller by the user to open the vault door. 

Here is an example of a 4x4 matrix keypad:

Display (16x2 LCD):

I’ve used a LCD display to show the instructions & indications to the user. It is a 2 line 16 Character

Display driven by the ATmega328 micro controller. 

The example picture of the LCD panel is given here:

Connection Diagram of the LCD Panel:

The LCD is connected to the I/O pins of the Atmega328 micro controller. It gets data input by its data pins (D4 to D7) & the data is shown on the display. LCD (Liquid Crystal Display) screen is an electronic display module and it has a wide range of applications. A 16x2 LCD display is very basic module and is very commonly used in various devices and circuits. These modules are preferred over seven segments and other multi segment LEDs. The reasons being LCDs are economical; easily programmable, have no limitation of displaying special & even custom characters (unlike in seven segments), animations and so on.

A 16x2 LCD means it can display 16 characters per line and there are 2 such lines. In this LCD each character is displayed in 5x7 pixel matrix. This LCD has two registers, namely, Command and Data. The command register stores the command instructions given to the LCD. A command is an instruction given to LCD to do a predefined task like initializing it, clearing its screen, setting the cursor position, controlling display etc. The data register stores the data to be displayed on the LCD. The data is the ASCII value of the character to be displayed on the LCD. 

Here is an example of simple connection scheme of a LCD display.

Pin Function of the LCD Module:

Sensors (PIR & LDR):

PIR:  A Passive Infrared sensor (PIR sensor) is an electronic device that measures infrared (IR) light radiating from objects in its field of view. PIR sensors are often used in the construction of PIR- based motion detectors. Apparent motion is detected when an infrared source with one temperature, such as a human, passes in front of an infrared source with another temperature, such as a wall. This is not to say that the sensor detects the heat from the object passing in front of it but that the object breaks the field which the sensor has determined as the "normal" state. Any object, even one exactly the same temperature as the surrounding objects will cause the PIR to activate if it moves in the field of the sensors.

All objects above absolute zero emit energy in the form of radiation. Usually infrared radiation is invisible to the human eye but can be detected by electronic devices designed for such a purpose. The term passive in this instance means that the PIR device does not emit an infrared beam but merely passively accepts incoming infrared radiation. “Infra” meaning below our ability to detect it visually, and “Red” because this color represents the lowest energy level that our eyes can sense before it becomes invisible. Thus, infrared means below the energy level of the color red, and applies to many sources of invisible energy.

PIR Sensor

PIR with Fresnel lens

PIR Module Circuitry

LDR: A photo-resistor or light dependent resistor is a resistor whose resistance decreases with increasing incident light intensity; in other words, it exhibits photo-conductivity.

A photo-resistor is made of a high resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance.

A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has its own charge carriers and is not an efficient semiconductor, e.g. silicon. In intrinsic devices the only available electrons are in the valence band, and hence the photon must have enough energy to excite the electron across the entire band gap. Extrinsic devices have impurities, also called dopants, added whose ground state energy is closer to the conduction band; since the electrons do not have as far to jump, lower energy photons (i.e., longer wavelengths and lower frequencies) are sufficient to trigger the device. If a sample of silicon has some of its atoms replaced by phosphorus atoms (impurities), there will be extra electrons available for conduction. This is an example of an extrinsic semiconductor. Photo-resistors are basically photocells.

TO Learn more about This Project, Please Visit Below Link 

http://atozcircuits.blogspot.com/2017/05/bank-vault-security-system-with_7.html