Security is main concern for various buildings, houses and offices. For this purpose, there are a variety of security alarms available in market which uses various types of technology for intruder detection like infrared sensors, motion sensors, ultrasonic sensors, laser sensors, etc. We have also built some security alarms like this PIR sensor based motion detector and burglar alarm circuit. In this circuit we are going to build a laser security alarm which uses a laser light and a laser light detector circuit. It gets activated when someone crosses it.
Circuit Components
- IC LM358
- 555 Timer IC
- Laser light
- 150 Ohm, 10K Resistor
- 10 K POT
- 220uF capacitor
- LDR
- Breadboard
- 9 Volt Battery and Connector
- LED
Circuit Diagram and Explanation
In this laser security alarm circuit we have used LM358 Dual Comparator IC for comparing voltages coming from LDR. Comparator is configured as Non-inverting mode and one 10K potentiometer is connected at its non-inverting terminal. An LDR is used for detecting light or laser light with respect to ground through a 10K resistor. And the midpoint of LDR and resistor is directly connected to inverting terminal of comparator. A red LED is connected at output pin of comparator for indicating intruder detection. A mono-stable multi-vibrator is also used for activating buzzer and LED for a time period. And a 9 volt battery is used for powering the circuit.
Working of Laser Security Alarm Circuit
In this circuit we have set reference voltages of comparators by using potentiometer, we can say this sensitivity of the circuit. Comparator is configured in non-inverting mode. In this system we have placed laser light and LDR facing each other, so laser light continuously falls on LDR. Due to this a potential difference generated across the non-inverting pin of comparator, then comparator compare this potential difference with reference voltage and generate a digital output as HIGH. Before this we have configured 555 timer in mono-stable mode so we it required a LOW trigger pulse at its trigger pin to activate buzzer and LED. So we applied output of comparator at trigger pin of 555 timer. Even comparator’s output is HIGH when laser lights falls on LDR so at this time buzzer and LED are deactivated. When someone crosses the laser light due to this LDR lost the laser light and generates a different potential difference across the same comparator terminal. Then comparator generates an output as LOW. Due to this LOW signal 555 timer gets a LOW trigger pulse and activates buzzer and LED for a time periods that is defined by R1 and C1 at 555 timer circuit.
Main component of this circuit is LDR which detects dark and light. LDR is a light dependent resistor which changes his resistance according to the light. When light falls on the LDR surface, it reduces its resistance and when no light resistance of LDR become Maximum. Understand more about working of LDR in this Dark Detector Circuit.
The 555 timer time calculation formula in mono-stable mode is:
Time period T is given by :
T = 1.1 R1 * C1
Where T is time in seconds, R1 is resistance in ohm and C1 is capacitor in farads
To demonstrate this project we have used a small toy laser light.
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Comments
Nov 03, 2015
sir plz canu explain how to connect it on breadboard by stepwise by tomarrow
Dec 15, 2015
Thanks for your info and circuit diagram. Can you make a diagram of laser alarm with timer and manual reset?
Jan 27, 2016
Y can't using. Ic741 it is also a comparator
Feb 12, 2016
You can use LM741, but LM358 is newer and advance than 741, compare the datasheets of both the ICs.
Feb 12, 2016
Sir,the circuit is not working properly ,the led yellow led is constantly glowing without irrespective of the ldr resistance
Feb 23, 2016
Adjust the Variable Resistor RV1 and check circuit connections.
Feb 19, 2016
can you let the buzzer run a little longer that
Feb 23, 2016
yes, you can run the buzzer longer, by changing the R1 and C1, as 555 is running in Monostable mode. Check this article: Monostable multibrator
Jul 23, 2018
should i reduce R1 and C1 or increase their values to run the buzzer for longer time
Feb 21, 2016
i need clap on and clap off switch
Feb 23, 2016
Here it is: Clap On Clap Off Switch and Clap Switch using Arduino
Mar 01, 2016
how much time does LDR require to get adjusted to laser light beam??
Mar 01, 2016
In the circuit you have used 5 resistors but in the demonstration video you have used four resistors...which resistor have you removed???
Mar 13, 2016
Why use 150ohm resistance
Mar 28, 2016
@Smitha and @priya: Follow the circuit diagram
Mar 20, 2016
WHAT IS THIS 7805.
Mar 28, 2016
It is a Voltage Regulator IC to provide the constant and smooth supply of 5v voltage.
Apr 07, 2016
Sir, why the IC555's 5th pin has opened.. Where it will be connect..??!
Apr 18, 2016
Learn about 555 timer IC here: Understanding 555 Timer IC
Apr 10, 2016
what is the intensity of the laser light source used??
Apr 22, 2016
Where did you get that laser light from and how much did it cost.
Also your breadboarded circuit does not look similar to the schematic. So if i do this circuit using the schematic, will it work?
Also what is that component on the top in the schematic
Apr 27, 2016
laser usually costs about 1.5$ on ebay, all spot lasers will be ok !
i did like on this schematic, leds show that everything is working but buzzer doesnt gev any sound....
its voltage regulator , it converts 9v to 5 v..... http://dac.ge/pdfs/23/04750.pdf
Apr 27, 2016
you may also use toy laser light and ldr.
yes we used 7805 to convert to 5 volt nad 7809 for converting 9 volt.
Apr 28, 2016
Hi i made a laser security system with resistors 1k and 6.8k and fet transistor with buzzer and photocell and led
When the laser beam hit the photocell buzzer doesnt stop why is it so
May 17, 2016
Please use the components of mentioned values, different resistor values change the High time of Monostable mode of 555.
May 11, 2016
Is the 7805 compulsory? What happens if I don't use it
May 17, 2016
7805 is used for 5v regulated power supply. For this particular circuit, you can omit 7805.
May 26, 2016
What is the function of resistance R2?
May 28, 2016
R2 and R3 are forming a Voltage Divider circuit.
Jun 01, 2016
what is RV1 and 10k written under it
Jun 11, 2016
Variable Resistor of 10k.
Jun 06, 2016
I just wanna know about the capacitor. is it polar or non polar.. if it's polar.. what is the voltage rating?
Jun 11, 2016
Its polarized capacitor with Voltage rating 16v, you can use any 220uF normal cap.
Jul 08, 2016
Hello,
Need to know the 555 circuit , which i want to use for disable the Alarm after 10 mins once it get trigred by my secruity circuit.
Thanks
Vasu
Jul 13, 2016
i need a simple school project on door and windows security alarms
Aug 13, 2016
We have numbers of projects on Security system, check here: Projects on Security System
Jul 21, 2016
hello sir, is it possible to replace the 7805 with 7812?
Aug 13, 2016
You can simply remove the 7805 and directly connect the battery in this project.
Aug 21, 2016
Irrespective of laser light the sound is coming from the buzzer...what to do?
Aug 29, 2016
it can be used also in pcb and which plz tell
Sep 10, 2016
The sound comes as soon as the battery is connected irrespective of the ldr. It goes off after some time but never sounds again until battery reconnected.
Sep 21, 2016
Adjust the RV1 properly. Circuit is simple and should work easily.
Sep 24, 2016
I made it...all soldered correctly...buzzer and all ligHTS r working simultaneously
Sep 30, 2016
thanks the circuit worked !!
Oct 02, 2016
sir can you give us the pcb layout for this?
Oct 06, 2016
There are so many softwares available for Schematic to PCB layout conversion like Easy EDA, Fritzing etc. We have made tutorial for using Easy EDA for PCB conversion Design Your Circuits Online for Free with EasyEDA
Oct 14, 2016
sir if we remove LM358 ic ?
Oct 23, 2016
I guess my LDR is so sensitive that when I connected the battery my all circuit elements start running (Lights are turned on and buzzer is sounding) What should I do to fix it?
Oct 27, 2016
You can adjust the sensitivity by rotating variable resistor RV1 and so that it wont trigger in normal daylight.
Oct 23, 2016
Sir,When i give the connection to the Pot...The LED does not glow
Nov 04, 2016
Sir, my circuit is working in an opposite matter. when light falls on the ldr, led glows and in dark it does not glow. how to correct it??
Dec 02, 2016
Check the connection to LM358 IC's inverting and non inverting terminals.
Nov 05, 2016
Are there changes in the 555
Dec 06, 2016
Sir, if I remove 7805 from the above circuit, do i need to replace the 9V power supply by a 5V power supply ??
Jan 28, 2017
You can use 9v battery directly without 7805.
Dec 10, 2016
Sir plz tell me about how to connect the components in breadboard
Dec 23, 2016
how i can cross the lazier in my circuit...which is drawing in Proteus program???
how i can cross it in my program...to test it?
Jan 28, 2017
Use Proteus for drawing circuit and simulation.
Feb 06, 2017
Sir i done this project successfully. But i want to know the application and uses of this project
Feb 16, 2017
i am not being able to success in this project sir buzzer and yellow led is continuously activate no matter light is in ldr or not
Feb 07, 2017
I like the circuit. I am planning to do it, but before that i need your help on some questions
1: i am planning to connect about 5 or 6 LDR s. How to connect( serail or parallel) it to get best result ? ( does it work)
2:how to change r1 and c1( imcrese or decrease) for long buzzering ?
3 how to add a manual switch for turning off buzzer instead of turning off itself?
pls give me a best answer instead of links. I read a lot of articles still i didnot understand it.
Feb 08, 2017
I made the circuit but its not working properly when a put the laser on LDR light turns on and when I remove it it goes off tell me any solution
Mar 04, 2017
Adjust the RV1 (potentiometer) and check the connection with LM358.
Mar 03, 2017
Sir plzz tell me..here use 10k potantiometer just like preset...can i use 10 k potentiometr..sir tell me
Mar 15, 2017
Sir do we have to make the 555 timer in monostable mode before connectingit in the circuit
May 02, 2017
sir can I get an introduction,abstract,conclusion on the the project "laser security alarm using ic555 and lm358"
May 10, 2017
What is the value of voltage of the capacitor? Is that ceramic or electrolytic?
May 13, 2017
can I get a perfect working operation and methodology on "laser security alarm using ic 555 and lm358".
Jun 15, 2017
awesome i like it
Jun 29, 2017
sir how can this be connected together with an arduino and a keypad....
Jul 05, 2017
Its far easier to build it using Arduino, you can connect alarm with any general purpose pin of Arduino and program it to trigger when LM358 is high. Search using search box above for these kind of project.
Jul 03, 2017
Sir,,I am new for Micro- controller project program.plz,,help me.I wanted made of micro- controller project
Jul 25, 2017
What is that 10k parallel to R4?? Please reply.
Aug 23, 2017
Can i increase the buzzer time in the circuit.
Aug 26, 2017
great minds with great ideas like the project
Sep 23, 2017
Sir, I am working on a project to sense the point of laser intrusion and send the alert message about the intrusion and location of intrusion.I am a beginner.Can u please tell how this can be implemented?
Sep 24, 2017
sense the point of laser intrusion?
I think that can be done by using multiple LDRs and read every one to know which LDR has been affected by the laser intensively. Since the position of each LDR is already known we can determine the positoin using the same. Just an idea hope it helped.
Sep 26, 2017
sir can you tell me what is the function of each components? thaaaanks
Oct 08, 2017
Great project , can you provide Proteus file for this simulation ?
Thanks in advance.
Oct 13, 2017
Wer did you put the other one resistor? In diagram it has 5 resistor and when you do it on breadboard it just 4 resistor.. Pls answer
Oct 26, 2017
how to set the reference voltage in pot
Oct 26, 2017
A pot will have three pins. Connect both the exterme pins to +5V and ground. Now connect the center pin to place where you have to set reference voltage. You can measure the current voltage by placing your multimeter lead on the Ground and the center pin of your POT
Oct 30, 2017
Sir, what is the meaning of arrow from LM358IC to RV1.
Is it a connection to RV1 above or below?
Oct 31, 2017
Sir . In ur circuit above.. how many seconds that the byzzer activate
Oct 31, 2017
sir plz can you explain how to connect it on breadboard by stepwise by today
Nov 22, 2017
Am getting an error using proteus to do the simulation of the project. Errors include
Transient GMIN stepping at time =5.145e-005
Tran: timestep too small= 1.25e-019.
Please I need help am doing it as my final project
Nov 22, 2017
Sir, why did you use Variable Resistor RV1 instead of a Fixed Resistor?
Nov 22, 2017
can you give me the Pcb( printed circuit broad) layout
Dec 02, 2017
when I do it on OrCad there is error because pin 5 is unconnected . Any help to solve this problem?
Dec 04, 2017
You have to place a no connection (NC) symbol to all unconnected pins in orcad, only then it will work
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