Laser alarm

what's an alaram

Well..suppose a theif enters ur home..u hae this laser alaram..if he walks between the laser and cds setup..buzzer goes off..hope it helps in understanding

Oy vey. He's being facetious. It's A-L-A-R-M, not alaram. Sounds like some kind of food for a male goat. "I'll have the grass a la ram." ;)

Anyhow, as for the circuit... You don't have the wiper hooked up to anything, so the pot is just acting as a 1k resistor. Ground the wiper. Set the resistance to 1M. Now you have a variable resistor from 10K to 1M. That should be close to your CDS by what you describe. Now that 7K that is on top of your voltage divider, in this circuit, 47K works pretty well. In real life, that value is going to depend on exact values from the CDS, and the turn on voltage of the MOSFET. If you aren't good with the math, understanding voltage dividers, and understanding MOSFETs, then I suggest you breadboard the circuit. Then get 10k, 22K, 47k, 68k, and 100k resistors and see which one works best.

Consider the following: do you need pinpoint accuracy? Do you need the light barrier to be quite lengthy? If not, there's no need to use a laser- but if you do then I would suggest using a phototransistor instead of LDR. Simple break-beam >a-l-a-r-m< circuits can be accomplished by means of less focused and/or specialized components like an IR-LED, LDR, Op-Amp as a comparator, transistor and a relay. And a few resistors ofcoz. That little circuit is fairly simple, straightforward and cheap, and will give you a reliable and invisible break-beam of 3 to 4 meters. However, the lack of a "light source" component makes these kinds of circuits a bit tricky to simulate here. It would be faster to breadboard the damn thing irl than dream up some clever solution around the absence of necessary parts..

Pull a VCR apart, there are at least three IR emitters and detectors inside to position the tape, all matched ready to go.

VCRs are great. There's ask kinds of good stuff inside, and nobody gives a crash how many you tear apart.

No Friggin Kidding! I disassembled my first one just a couple weeks ago- those little IR towers are cool, so are the nifty gear assemblies. What's really awesome are the heads- machined aluminum cylinders with incredible bearings that allow it to spin really fast and really quiet!..

Yep. All kinds of cool mechanical and electrical stuff. I've been asking everyone I know for their old VCRs for like a year lol.

Hell yeah, you're like "..wow really, you STILL have a VCR around?! Well check it out I'm heading to the e-cycling place tomorrow to get rid of some of my old junk- I could take that VCR down there too if you want..." heheheh.. X^D

Hey @ally21- besides our excitement over vcr's, has anything been helpful?..

Use a latch to latch it on

I did some further search...a thyristor and capacitor might solve the problem..i tried capacitor alone in the circuit..but didnt work

Try to replace ur mosfet to BJT and ur potentiometer is too high👍👍