Laser or IR beam alarm system

[mrkedar_kyk]

as..... ordinary

your project was really amazing
i like it very much.

 

[Amarr]

**broken link removed**
this site contains some tent oriented ideas view it

 

[tmurali]

This is a cool little circuit that i made for a school project. It can be used as one of those things that is usually seen on the door of small shops so that when someone walks in it goes "ding dong". It could also be used as a burglar alarm (just need to get a loud enuf siren).

A light has to be pointed at the LDR. It can be anything, just as long as its bright enough. Im pretty sure that an infrared LED would work, a regular light, or my personal favorite: a laser pointer, just like in the movies 8) . You could encircle your house w/ a laser so wen someone crosses the beam you know.

R1 can be adjusted for sensitivity of the circuit to light. The lower R1, the more sensitive, and vica versa. The value of R1 will not allow the circuit to work in direct or indirect sunlight. R1 would have to be increased to make the circuit less sensitive to light (even then i doubt it would work in direct sunlight). An alternative to this is putting a tube on the LDR that is a couple centimeters long so that only light from the light source could get in.

R4 can be adjusted for how long the buzzer stays on. 100k makes it stay on for about 9 seconds. Or the value of C1 could be adjusted.

Someday i plan on putting a transmitter on the circuit so that it could be put out in the yard, and a receiver inside would go off. HAVE FUN :lol:

could you give the values of pnp and npn's

 

[henok]

what is the value of the transistors

 

[henok]

hello

hi how are you i am from ethiopia & i am electronics student .
i really need to know the values of the transistors.

 

[slamslam123]

power line communication

hi guys . if any person has information about the voice over power line, please give it to me

 

[blueroomelectronics]

hi how are you i am from ethiopia & i am electronics student .
i really need to know the values of the transistors.

Page 2 of the thread.

 

[KlatuClassic]

Hey Zach, I am in Temecula and would like to pick your brain about the beamed alarm idea. Are you still around? Jim

 

[DarkFel]

Yes, sorry, I'm not English, But I try to speak my mind :
I tested your circuit on my computer with the following program : crocodile physics, it works perfectly, but I don't know what's transistors I need to do it... 2N2222 and 2N3904 could be work ? Thanks

 

[Torben]

hi friends,
need help? Unable to make the circuit small? Tey Printed circuit board(PCB) form me. just send me the circuit i will send you the netting.

Hey there,

Look, you're welcome on the forum, but if you have a business to advertise then just but a nice discrete link in your .sig and only post relevant posts. This is not a place to advertise, it is a place to learn and to teach.

Be polite, don't spam, and don't post in threads unless you have something to add to the discussion which is already happening. Don't start your own threads if the only point is to spam us.


Torben

 

[elitesky]

Hi masters, can I ask something? What kind of laser is strong enough to trigger an LDR? Ive been thinking of a simple cheap laser pointer which is battery powered but I wonder if its strong enough to trigger an LDR placed about 2 feet away. And does anyone have an idea of a kind of laser that can be plugged to an outlet? because the battery-powered one cannot last long and becomes weaker. Because i also have a project, its an obstacle scanner. the LDR and laser is mounted on opposing conveyor belts, and the space is between is scanned for obstacles. thank you in advance

 

[Torben]

Hi there and welcome to the forums,

First off, I am a master of nothing except perhaps my own boots. That said, a cheap laser pointer will be more than enough to use with an LDR. It will depend a lot upon the circuit and the actual LDR in question, though.

Can you post the schematic you intend to use?


Cheers,

Torben

 

[elitesky]

i still dont have schematics. we havent started doing it, since it is in proposal stage and we are deciding what materials to gather. and im no electronics practitioner, it is a part of our project in parallel port interfacing. the laser and LDR is moved horizontally on separate conveyor belts to scan a surface. so basically, the LDR and laser should be far apart about 2 or 1.5 feet. here's the setup in the attachment..

 

[Torben]

LDR should work fine, although I'd probably use a phototransistor as a receiver instead of the LDR. LDRs are slow compared to phototransistors. Photodiodes are faster yet, but I have LDRs and phototransistors around and no photodiodes.

You will need to account for ambient light rejection, so the receiver will need to be shielded and you might want to look at modulating the laser so that ambient light won't interfere. Shielding is easier if you're not that into electronics though.


Torben

 

[elitesky]

yeah we are planning to remove as much ambient light as possible by shielding the LDR, or the whole setup itself. thank you for ur suggestion ^^

 

[ia123]

i know this is jind of stupid question. Im in year 10 and making several sequrity systems for my GCSE grade. How can i make the buzzer go on indefinetly untill the circut is reset?

 

[dead_man]

Laser Or Ir Beam

wht is the number/name of the transisrte you used in the cicrut.plz let me now quick

 

[ia123]

fixed it

I found if i just stuck a high value capistor there then it went on for virtually ever. well long enough for some one to hear. Thx anyway

 

[xanne0037]

i am a computer engineering student.. i need this kind of circuit too for my school project. is it possible to supply a laser pen by an AC power so it will be plugged in not worrying about it's battery?

is LDR doesn't have any code description? i mean, do suppliers will give what i need by simply asking for an LDR?

 

[Dirk.S]

i am a computer engineering student.. i need this kind of circuit too for my school project. is it possible to supply a laser pen by an AC power so it will be plugged in not worrying about it's battery?

is LDR doesn't have any code description? i mean, do suppliers will give what i need by simply asking for an LDR?

Yes you can connect it up to a transformer, but first you need to check the ratings of the laser pointer, i.e. what the max amount of voltage is it can take. Than if you only have tranformer with a certain output which is not the output you want, you willl have to incorperate a step-up or a step-down circuit to get the voltage up or down.

To the locals, sorry not trying to revive this thread or anything. I was just doing some research and looking into this thread since I also want to do this project. once I'm done with mine I'll post it here, may take a while so please be patiant. Just a word of respect for you guys for all your patiance. Hope you all have a great day.