Laser alarm

[LaserAlarm]

Looking to build this laser alarm. I need some help. Never made anything like this before.
Web page with the idea Protect Your Home with Laserbeams!

**broken link removed**
**broken link removed**
Is this the correct way to do this? If not please correct.
Thanks Dan
Minnesota

 

[LaserAlarm]

If you break the infrared beam to the photocell it will set off the siren. But if you let the beam hit the photocell it will turn off the siren. Where would I add a relay to this setup to keep the siren on after your break the infrared beam of light? And what type of relay should I use? Would this setup work?
I am a beginner.

 

[john1]

I dont think that circuit is right.
Maybe the battery has been drawn in the wrong place.

 

[LaserAlarm]

Is the schematic right?

 

[Andy1845c]

Google "dark detecting circuit" and you will find some other ways this can be done. Many use a photo transistor insted of a photocell. The circuit you posted and the one on the site you posted the link for don't look right to me (i'm not an expert though).

To hold the alarm on you could use a latching relay or possibly a 555 timer in monostable mode. (Google "555 timer" and you will get loads of info on them, or search this board.) It all really depends on your alarm buzzer and how much current (amps) it draws. A 555 can only handle 200mA. You show a 9v battery and a 12v buzzer. The buzzer might kinda work at 9v, might sound sick or might not work at all. Running everything at 12v would be better.

This is kind of a hooky alarm. I wouldn't trust it to protect anything valuble in real life, but it certinly could be fun to make.

The way they show holding the little mirrors up is awful crude. I would imagine they will slowly sag and misalign the beam and set off a false alarms.

 

[blueroomelectronics]

Mirrors Lasers careful you'll loose an eye kid.

 

[Mikebits]

Laser safety - Wikipedia, the free encyclopedia

 

[john1]

Hi Dan, (LaserAlarm)

Was this question for me ?

Is the schematic right?

I was hoping someone else would recognise the arrangement, and post a correction.
The schematic and the picture are both the same circuit, and i feel they are both wrong.

Ive rearranged the schematic, as i feel it should be.
Please rearrange the picture suitably.

I also feel that a darlington would be more suited, with a ten or twenty K pot instead
of the 5 K shown.

Not sure at all about that 1000 Mfd, but then i haven't actually made this unit,
maybe its fine.

Best of luck with it,
John

 

[LaserAlarm]

john1

No

Its for any one who can help or has an idea.

 

[ericgibbs]

john1

No

Its for any one who can help or has an idea.

hi,
As I understand you want a 'red' continous laser beam to strike a light detector.

As long as the beam is hitting the detector you dont want the alarm.

When the beam is broken, after a very short delay you want the alarm to sound for a few seconds, even if the beam is restored.

Is that close.?

 

[LaserAlarm]

ericgibbs
YES

 

[ericgibbs]

ericgibbs
YES

Its always best to ask,

That circuit as its drawn on the link is duff.!

If it was rearranged it could be made to work, but its a poorly thought out circuit.

What laser do you have and whats the distance you want to cover.?

Is it indoors or out.?

Lets know, I could draw out a circuit for you.
Have you access to the 'usual' range of components.

 

[LaserAlarm]

Indoors 16'
I think I found a cheap setup. Use a photocell nightlight, hooked up to a siren and shoot a laser beam at the night light. If laser beam is broken siren comes on. What type of relay should I use to keep the siren on? This might work.

 

[Willbe]

As drawn, light on the cell turns off the siren.
If you can get resistance specs on the photocell we all can redesign.

 

[LaserAlarm]

Going to use a laser. Something like this. Only has to go 16', for inside a garage. If you break the beam of light the siren will sound.
**broken link removed**
Use a night light like this **broken link removed** this night light takes a 7 watt bulb. I would have to find a 7 watt siren or could I increase the volts some how?

 

[john1]

There are many PIR units, some with lamp attached for indoor and outdoor use.
You could replace the lamp with a bell or siren easily.
That would be even less trouble.

They run straight from the mains, no supply unit to make.
No laser to set up, just position in a suitable place.

Some are quite cleverly made, and can even be adjusted to ignore a cat
or small animals.

John

 

[LaserAlarm]

john1
Something like this?
**broken link removed**
**broken link removed**

 

[john1]

Yes, thats the sort of thing.
Check that it will run from the mains supply,
and that it has an output to run a lamp or some small load.

Some of them look like that, and have no relay fitted,
Or dont run from the main supply.

John

 

[john1]

The ones that come with a lamp attached
usually run Ok from the mains,
and switch a mains lamp.

John

 

[Valence_4]

PIR detectors are designed to detect movement nearby it. For that, it detects far infrared light emitted by a warm body (such as a human being.) I'm not sure it will detect red light from a laser. Also, PIR's are equipped with special fresnel lenses that will concentrate multiples FIR beams to the detector cell as someone passes nearby. So you'll need to turn on-off the beam a few times to activate the relay. A single "cut and recover" event will not activate the PIR motion detector.