Smart Laser Alarm Protection using IC 555

The post discusses the making of a simple yet effective smart laser alarm protection circuit using the IC 555, for securing a specified restricted zone from human interventions. The idea was requested by Mr. Collins.

Protecting Home with Laser Alarms


I just want to tell you what an amazing passion and dedication to electronics you have and thank you for helping others like me. My name is Collin from south Africa.

We have a huge problem of safety here.

There are countless number of robberies and house break inns its so unreal. I was hoping you can help me with regards to a circuit for a very cost effective and reliable product.

I have built a laser tripwire alarm using a 555 IC timer but the circuit design lacks a lot of features.

I need something that as soon as an intruder enters my property I will be alerted before they even get a chance to try and get into my home.

The circuit needs the following: Once alarm is activated it needs to sound for a few minutes and then go off

and arm again automatically. Don't want it ringing for hours in end if I am not at home to reset it.

It should not be triggered by pets or flying debris in the yard.

Easy alignment of the sensors. The laser alarm works OK but its very difficult to set the pointer on the LDR that keeps moving off. Any tips if we are going than route?

It doesn't have to be a laser system I am open to whatever you think will solve my problem.

Thanks a lot for everything and feel free to add whatever you think I missed out with regards to all the features.

Kind regards

Collin

The Design


Parts List


R1, R4 = 100K
R2 = 1M
R3/C2 = TO BE CALCULATED (SEE TEXT)
C1 = 4.7uF/25V
IC = ANY 555 VARIANT
C3 = 10nF
C4 = 0.33uF
ALARM = 12V, 200mA PIEZO ALARM.
LDR = any standard




IC 555Pinouts



Simulation and Working


The proposed smart yet simple laser alarm circuit using IC 555 can be witnessed in the following image, the functioning can be understood with the following points:

1) The IC 555 is configured in its basic monostable mode.

2) Pin#2, which is the trigger input of the IC can be seen connected with the emitter of a PNP BJT via a blocking capacitor C2.

3) We can also notice a couple of parallel LDRs secured within opaque pipes and their leads hooked up with the base of the PNP BJT, such that as long as the LDRs remain illuminated together through the laser light focus, the BJT remains deactivated. This happens because in the presence of laser light the LDR's combined resistance drops to around 30K, which keeps the base of the PNP more positive than the ground bias from R2.

4) The inclusion of two LDR ensures a fool proof alarm set-up such that only a human presence is able to interrupt the LDRs, while these remain unaffected by other smaller irrelevant intruders such as animals, birds etc.The two LDRs could be placed at a distance of around 2 feet so that only taller objects such as a human being gets detected.

5) Therefore whenever an interruption in the laser beam is detected, the LDRs go through a sudden rise in their resistances causing T2 to switch ON, which in turn triggers pin#2 of the IC via C1.

6) This prompts the IC 555 to activate its pin#3, which finally activates the connected alarm unit.

7) Since the IC 555 is configured in its monostable mode, the pin#3 remains activated only for a period determined by the RC network at pin#6 and pin#7 of the IC, or by R3,C2.

These timing components can be appropriately calculated using the IC 555 calculator software for accomplishing the desired length of time for which the alarm may remain switched ON.

How to Set Up the Laser Transmitter Units


The laser transmitter devices could be installed near the LDRs itself and focused back to the LDRs using mirror reflectors as shown below:



The installing of the laser devices near the LDRs allows the entire unit to be installed inside a single enclosure and also allows the lasers to be powered from the circuit itself.

This also facilitates securing the lasers and the LDR units firmly and accurately so that both the counterparts are unable to move or deviate from their positions even in an event of a mechanical shock or other vibrational interferences.

The mirrors could be positioned at some specified distance, exactly opposite to the laser installation , making sure that the laser beams intersect the restricted zone and the presence of a possible intrusion is detected without fail.

This concludes the making of the proposed IC 555 based smart laser alarm protection circuit, if you have any doubts please feel free to put them forth in the below given comments box.

Using BJTs for Reducing Current Consumption


The above design can be further enhanced to work with lower standby current, and also with a battery backup during of power failures, through the following upgraded schematic:


Laser Security using Single LDR


If you intend to simplify the implementation for a single LDR operation, in that case the following concept can be tried:


Need Help? Please send your queries through Comments for quick replies! And please Bookmark my site :)




Comments

debasisneogi said…
"Smart Laser Alarm Protection Circuit using IC 555"
Sir, what can be the distance between the laser illuminator and mirror in the subject circuit.
It is a wonderfull website!!!!
Dragon Monkey said…
Im the 1 of followers of you Mr swagatam majumdar. I like your circuit diagram.
Swagatam said…
Debasis, it will depend on how far the laser is able to travel and reflect back on the LDR without losing the required intensity..as long as it is able to implement this, it will work regardless of the distance...
Swagatam said…
I am glad you liked my circuits, thanks for visiting my site!! and keep up the good work
NvD said…
sir
can u give me a simple circuit for charging 12v 7.2ah battery
Swagatam said…
NVD, you can connect the battery to a 14V/1Amp DC source and allow it to charge for 12 hours and then remove it....
Dragon Monkey said…
Mr swagatam I want to know the value of R3,C2,T1. Thank you.
Swagatam said…
it's 100K, 100uF/25V and BC557
NvD said…
thank u sir
gowthaman s said…
Can you give me a fluorescent lamp electronic choke design for 36 and 40 watts . Input of 230 v 50 hz supply
muthukumar said…
Hai sir i am one of the follower in your blog,Can u give homemade led street light drawing.
Swagatam said…
you can try the following design

https://homemade-circuits.com/2015/11/120v-220v-electronic-ballast-circuit.html
Swagatam said…
Hi Muthukumar, you can try the following circuit

https://homemade-circuits.com/2016/12/simple-solar-led-street-light-system.html
Subrahmanyam G said…
Hi sir, i am from india and very much need of undermentioned circuit. Kindly help me.
After selecting 4 or 16 position in a selection knob , and pressing of push button , first 4 or 16 LEDs out of 32 should glow one by one then stop, again after push of push button 5 to 9 LEDs should glow with 1 sec gap. As it is required to teach my students and I have only mechanical background, i could not make it.please help me.
Swagatam said…
Hi Subramanyam, first I would suggest you to make the last circuit from the article which is mentioned below...and succeed making the 18 LEDs run in sequence, once you make this I will instruct you how to proceed further...

https://homemade-circuits.com/2011/12/how-to-make-18-led-light-chaser-circuit.html
Subrahmanyam G said…
sir, i made the above said circuit.kindly guide me to get desired result as said earlier
Swagatam said…
Subhramayam, what kind of sequencing are you getting, I am sure it's one led at a time, do you need this kind of sequencing or do you want the subsequent LEds to latch and glow constantly as the sequence proceeds?

for the second option you may have employ small SCRs at the 49017 outputs so that the LED illumination can get latched while sequencing?

after this you will need selector switches for selecting the desired sequence lengths
Swagatam said…
i mistakenly mentioned 49017...actually i meant 4017
Subrahmanyam G said…
Thanks for such a lightening reply. After selecting 4 or 16 position in a selection knob , and pressing of push button , first 4 or 16 LEDs out of 32 should glow one by one then stop, again after push of push button 5 to 9 LEDs should glow with 1 sec gap.
Subrahmanyam G said…
In above circuit all leds of first ic glow, the leds of second ic strts glowing ,but leds of first ic also simultaneously glowing, which is not required, kindly solve my problem
Swagatam said…
that means each subsequent LED must stays illuminated while they sequence..you will have to employ SCRs at the outputs for acheiving this
Swagatam said…
no that shouldn't happen? LED sequencing is supposed to start from the first pin of one IC and go on sequencing one after the other until the 18th LED on the last pinout of the second IC is reached, after this the sequence must revert to the initial pinout of the first IC and the cycle must go on repeating in the same way...please first diagnose and correct the fault in your design
paul said…
Hi im just about to build this circuit for my back yard security, what ohm LDR do i need , havnt done electronics for 15 years im a little rusty! thanks for your time
paul
Swagatam said…
Hi, you can use any LDR whose resistance is able to drop to approximately 50K in ambient light (not direct light), and rises to infinity in darkness.
Sidhesh dessai said…
Hi sir can u give me idea to build revolving search light ,
Swag said…
Sidhesh, do you want it using a motor or without a motor through chasing LED simulation?
amal said…
What is the value of R3
and C2
Swag said…
use the first software from this link to calculate it

https://circuitcalculators.blogspot.in/2017/10/ic-555-calculator.html
JAYANATH said…
dear sir
i want to make mid night lamp which should be on 12 mid night and off at morning 4 o clock. timer or LDR circuits not effective for exact timings (while power off or bad light conditions) therefore i want use a digital clock for time input . please set instructions
Swag said…
Dear Jayanth, you can try the following concept and modify according to your particular needs:

https://www.homemade-circuits.com/making-programmable-timer-circuit-using/
nurul said…
hi . i'm still new on this . and i don't know how to use the ic 555 calculator software . can you tell me what kind of value of R3 and C2 can use ?
Swag said…
You can try 100K and 22uF/25V..if the delay is not sufficient for the alarm, you can keep increasing them until you find it OK!
nurul said…
admin . did you have the formula to calculate the value of R3 and C2 ? other than use ic 555 calculator software.
Swag said…
yes, here's the formula:

Time Out Delay (secs) = 1.1 * R1 * C1
nurul said…
thank you admin
nurul said…
admin . may i ask what is the safety of this circuit need ?
Swag said…
for safety use only 12V as the supply, and use a small buzzer at the output, for high power buzzer you may have to use a transistor driver at pin#3 of the IC
nurul said…
sir, actually I already try to install the circuit like the circuit you show . but the sensor is not working . when i connect the power supply the buzzer make a sound . can you guard me sir until my circuit is work ? i need to send my project in this week . please...
Swag said…
Hi Nurul, yes I'll guide you until you are are able to complete this project, first tell me how many LDRs are you using, a single or two?
Nurul said…
2 LDRs for 2 doors
Swag said…
In the above diagram both the LDRs needs to be blocked for the action, how do you wish to operate your system? If you wish the alarm to sound if any one of the LDRs are blocked, then the LDR wiring will need to be in series, and the transistor configuration will also change.
Nurul said…
I still can't imagine it . Can you draw the circuit ??
Swag said…
how do you want the LDRs to sense and function, when both are obstructed together, or each one independently and separately? meaning if any one LDR is blocked the alarm will be ON.
nurul said…
each one independently and separately
Swag said…
I'll show you how to wire the LDR and then you can check it...
nurul said…
i want the LDRs to sense separately.
nurul said…
okey . i will waiting for it .
Swag said…
I have updated the diagram at the end of the post, please check it and make it exactly as shown...it will work as required by you.
nurul said…
can i request the diagram of LDRs to sense and function when both are obstructed together ?
Swag said…
Add one more LDR in parallel to the last diagram...then both will need to obstructed together for activating the alarm
nurul said…
okey . i need to buy the components first . tomorrow i will construct it . i will inform you if it success or not
nurul said…
admin . the resistor 1M that have arrow, is that potentiometer ?
Swag said…
OK, it'll be a success for sure, there's no doubt!
Swag said…
ye that's a variable resistor or pot, but you can replace the two resistors with a single fixed one.
Nurul said…
If I using 2M instead 2M2 is it Okey ? Cause I can't find 2M2

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