project report electronic design topic laser security alarm circuit

HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGYSCHOOL OF ELECTRICAL ENGINEERING---PROJECT REPORTELECTRONIC DESIGNTOPIC: LASER SECURITY ALARM CIRCUIT... We aim to develop an affordable,user-fr

HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY

SCHOOL OF ELECTRICAL ENGINEERING

- 

-PROJECT REPORT

ELECTRONIC DESIGN

TOPIC: LASER SECURITY ALARM CIRCUIT

Supervisor

Nguyễn Cảnh Quang

Authors

Lê Quý Dương 20212402

TABLE OF CONTENT

LIST OF FIGURES 3

CHAPTER I: INTRODUCTION & OVERVIEW 5

1 Problem statement 5

2 Main objective 5

3 Scope of work 5

1 General concept 6

2 Block diagram 6

1 Circuit Component 7

2 Schematic Diagram 7

3 Comparator Block8

4 Transistor Block 9

5 IC 555 Block 11

CHAPTER IV: RESULT AND IMPLEMENTATION 14

LIST OF FIGURES

Security protection systems are often known to be expensive This project addresses the challenge of utilizing lasers to construct a basic security system The market is filled with security systems that make use of lasers Most of them consist

of two parts: the infrared motion detector and the alarm The system we construct for this project employs a photoresistor to sense variations in light intensity If there is an interruption in the laser beam shining into the LDR, the system will alert the user through the speaker We aim to develop an affordable, user-friendly, and highly efficient security system for apartment usage

The laser security circuit's mechanism will be presented in this study We will go over the functions of each section, the significance of the circuit's components, and the steps involved

in creating laser security circuits

CHAPTER I: INTRODUCTION & OVERVIEW

1.1 Problem statement

Security and safety are one of the leading factors in people's lives With crimes and thefts becoming more sophisticated, people increasingly pay more attention

to security systems

A popular security tool is the laser security alarm system It can be used for various security purposes, from basic home maintenance supplies to precious business assets They were once a costly option for security requirements Understanding the value of security systems, we suggest a straightforward, inexpensive, and practical laser security protection circuit

1.2 Main objectives

For the laser security circuit project, we need to achieve the following goals:

- Draw a block diagram of the necessary components to make up an electrical circuit Learn clearly about the working process of those devices

- Perform calculations to choose the correct specifications for the components in the circuit

- Simulate electrical circuits on Proteus simulation software

1.3 Scope of work

This project is designed as a security system used in apartments The components used will be popular components on the market The cost of the circuit will be around 20,000-30,000 VND

CHAPTER II: METHODOLOGY & APPROACH

2.1 General Concept

One of the important components that determines the properties of this circuit is LDR (Light Dependent Resistor) We use LDR in series with a resistor

to form the first voltage divider circuit, and a potentiometer to form the second voltage divider circuit Next, an op-amp with a comparison function will be used These two voltage divider circuits will determine the inverting and non-inverting input voltage of the Op-amp, thereby controlling the output state of the Op-amp to be High or Low If the output of the Op-amp is High, the transistor will conduct and vice versa

As the output of the transistor is connected to the Trigger Pin (Pin 2) of the 555 Timer IC, if the transistor is ON, the trigger pin gets a short low pulse and as a result, the output of the 555 becomes HIGH This will activate the alarm by turning ON the buzzer Until the reset push-button is pushed, the alarm will stay on hence, we can place the reset button at a secret location so that only the owner can disable the alarm

2.2 Block Diagram

6 LDR

LIGHT

SOURCE

OP-AMP

IC555 TRANSISTOR

Power source

CHAPTER III: CIRCUIT DESIGN

3.1 Circuit Component

IC NE 555 Pulse generation IC Buzzer Active, Rated voltage: 3V

Button

3.2 Schematic Diagram

Figure 1: Schematic diagram

3.3 Comparator block

As a light sensor, we employ LDR The resistance of a Light Dependent Resistor (LDR) is just a few tens to a few hundred Ohms when it is illuminated The resistance value of the LDR rapidly rises to several Mega Ohms when there is no light coming in We create a voltage divider circuit by

connecting the LDR in series with a resistor of

10 KΩ To guarantee that it is substantially higher than the LDR value while illuminated and significantly lower than the LDR value Figure 2: Comparator block

when unlit, the value of 10 KΩ was used Similarly, a 10 KΩ variable resistor with adjustable resistance is also used to create a voltage divider circuit The op-amp in this circuit will operate with a comparator function It will contrast the input voltages that are inverting (pin 2) and non-inverting (pin 3) Vo (pin 1) will go up to +VCC when "V+" is greater than "V-" and drop to GND when "V-" is greater than "V+." The non-inverting input voltage will be determined by:

V + ¿¿= Vcc

R LDR + R 1

RLDR

The inverting input voltage is calculated similarly and can

be adjusted at will via a potentiometer

We decided to choose IC LM358 as the voltage comparison task It is a common IC with high accuracy and low price The maximum Vcc voltage supplied to this IC is 32 V, which in our case is 9V Therefore, we can use this IC in the circuit

Figure 3: IC LM358 schematic

Figure 4: IC LM358 datasheet,

3.4 Transistor block

The transistor in this circuit will act as an electronic switch We choose transistor BC547 as a common NPN transistor, which can be used to replace many types

of transistors With such a function, we will choose the transistor to operate in two modes: cut-off and saturation, corresponding to the open and closed states of the switch When the output of IC LM358 (pin 1) is Low, Vbe< 0.7 V, the Transistor will be in cut-off mode In this mode, the transistor essentially does nothing and it is assumed that the switch is not closed.When the output of the Transistor is High, the output voltage is equal to Vcc, and the transistor will be in a saturated state, while C-E and B-C will be forward-biased and considered closed switching The reason for choosing a transistor that operates in saturation mode is because in saturation mode, the voltage across the BJT is low and the power dissipation in the transistor is also low The collector current will reach its maximum value

To choose the base resistor for the transistor to operate in saturation mode: in saturation state, the current Ic increases to its maximum Currently, I c R c ≈ V cc

11

Figure 5: transistor block

v in(on) = 9V

v in(off) = 0V

V CC = 9 V

V RC

R B

v in

V CE

V BE

Vce(sat) of BC547 ~ 0.1V With the load resistor value Rc 10k Ohms, we can calculate the current I c :

I c = 9−0.1

10000=0.89mA The transistor reaches saturation when the current Ib is large enough with the formula: Ib β ≥ Icmax With βmin= 110:

Ib= 9−V be

R b

β ≥ 0.89 m→ R b ≤ 10Ω

To facilitate the purchase of components, we choose the value

Rb = 10K Ω, Ib= 0.83 mA

Figure 7: BC547 Datasheet

3.5 IC 555 Block:

Figure 8: IC 555 block

We want to design the circuit so that when the speaker beeps,

it will not turn off even if the transistor is not conducting We chose to use the NE 555 IC with its flip-flop In this circuit, IC

555 operates in bistable mode Here is the structure of IC NE 555:

Figure 9: Structure of IC 555

The output of the transistor is connected to the Trigger Pin (Pin 2) of the 555 Timer IC When the transistor is On, the input voltage to pin 2 is < 1/3Vcc, the output of op-amp C2 is High, and the output of op-amp C1 will be Low We have the following truth table:

Figure 10: Truth table

The logic of the gate Q is Low, so output pin 3 is High and the buzzer will sound When the transistor is in cut-off mode, the logic levels of S and R will both be Low According to the truth table, the output logic level of the flip flop does not change, meaning it still is in the previous state and the buzzer still sounds The buzzer only turns off when the user presses the button connected to the reset pin of IC 555 When the button is pressed, the Reset pin input will be connected to the ground, transmitting a Low signal and causing the output to return to Low, the speaker will turn off The voltage value of pin 5 = 2/3 Vcc, capacitor C1 is connected to pin 5 to form an RC filter circuit to help reduce noise in the circuit Finally, a 10k resistor

is connected in series with the reset pin, corresponding to

Vcc=9V to ensure that the current does not exceed the maximum level

Figure 11: IC 555 Datasheet

CHAPTER IV: RESULT AND IMPLEMENTATION

We have successfully designed the laser security circuit The experimental model is performed according to the circuit diagram and the results are as expected The buzzer was turned on when the laser beam fell on the interrupted LDR The buzzer only turns off when the user presses the button Note that the LDR must be placed in the dark or wrapped with black

tape so that light sources other than the laser beam do not affect the LDR This helps the circuit operate faster and more accurately

Figure 12: Real circuit

CHAPTER V: CONCLUSION

5.1 Conclusion

Laser security systems provide us with safety against all crimes and thefts in daily life The circuit we design is highly efficient with low price, easy to access, and familiar to users Through applying learned knowledge and observations in practice, the

circuit design process has helped improve knowledge about electronic components However, this circuit still has some limitations and will be improved in the future

5.2 Future work:

- Increase operating range

- Increase circuit operating time

REFERENCE

[1] “BC547 Datasheet (PDF),” ALLDATASHEET.COM - Electronic Parts Datasheet Search, https://www.alldatasheet.com/datasheet-pdf/pdf/586720/FAIRCHILD/BC547.html [2] “LM358 Datasheet (PDF),” ALLDATASHEET.COM - Electronic Parts Datasheet Search, https://www.alldatasheet.com/datasheet-pdf/pdf/3067/MOTOROLA/LM358.html

[3] NE555 Datasheet (PDF),” ALLDATASHEET.COM - Electronic Parts Datasheet Search, https://www.alldatasheet.com/datasheet-pdf/pdf/471200/STMICROELECTRONICS/ NE555.html