How long is a bit of string? Yes, there ARE lasers in existance which will be detectable after 30 metres and two mirrors but not all lasers... Also depends on how sensitive your receiving apperatus is, and the quality of your mirrors. I am afraid that I cannot actually comment becuase I do not really know much about how the power of a laser degrades over distance, or how to measure how perfect a mirror is in terms of incident power and relected power, but these are things that you have to find out. My personal experience of LDR's is that they are quite rubbish, but that is just me, there may be better ones which respond faster or there may be a better sensor for laser light. Rod
A idea i thought about while hearing about the lasers... Put the laster pointing to the street on one side of your house, and then near the street/sidewalk or somewhere, have a box or something hidden at a certain level that's the same height at each point of the house, and each point near the street. Have these boxes contain the mirrors, so that no one can see the red light. Also, put the laser itself in a box with a hole. At the end of the laser beam, get a light sensing device, and design a circuit that'll set off the alarm or light or whatever. You can do this with a relay.
detecting circuit Here is an exemple of the detecting circuit you could use: This was modified from the following: http://www.free-electronic-circuits.com/circuits/light-sensitive-alarm.html
OK, I finally got what I was looking for in that schematic. Only problem is, I have only dealt with VERY simple ones in the past. I know how to solder, and have been tinkering aroudn with little circuits, etc. Im assuming I can buy components at RadioShack, which is close to me here in the States. This is the same schematic with 6 numbers on it, each representing an area that isnt quite clear to me or I want to reassure myself. I assume the diagram is with a laser constantly on, pointing directly at the LDR. 1. When there is light on the LDR, it allows current to pass through the circuit to ground. When the light beam is BROKEN, it sends it to #3 2. The 12v source is dc, I am assuming. How many mA should enter the circuit at each of the 5 12v points? Secondly, what is the R6 100K thing on the left hand side that has #1, 2 and 3 near it? Is that an on off/switch? 3. What happens here? 4. I looked online and found that #4 is a chip that has something to do with timing. Im not quite sure what this does either. 5. When the wires come off the chip does this control how things go to #6? Finally, #6, does it control the alert device?
oh, btw i was playing around with a VERY cheap laser and found that high quality mirrors do a good job even with a crappy laser. I dont think that with a better laser I will have any problems.
You are right. For this circuit to work the laser needs to be pointing at the LDR. 1. This is a voltage divider, when the value at the transistor base changes (when the laser is no longer pointing at the LDR) the current flowing through R3 will also change. 2. Yes, it's 12V DC. If you have a 12V DC 200mA transformer it should enough (it depends what relay you use). The 100K is a variable resistor or potentiometer. It allows you to ajust the sensitivity. 3. PIN2 of the LM555 is about 12V (because of R4) when nothing interesting is going on. If the quantity of light changes quickly, the voltage difference observed across R3 will influence the voltage at PIN2 of the LM555 and bring it to a value close enough to 0V. C3 prevents a slow change of lighting on the LDR to trigger the system (innevitable sunlight reaching the LDR). 4 & 5. You can google 555 timers if you want to understand a bit more, but here is the big picture: When the voltage at PIN2 drops to about 0V, for even a really short time, the PIN3 output goes to 12V (normally it will be 0V) for an amount of time determined by the values of R1 and C2. The given values will leave PIN3 at 12V for about 60seconds. Increase either the value of R1 or C2 to increase the time you want your light or buzzer to stay on. At #6 the 2N2222 transistor drives the relay coil. You can connect anything you wish to the relay. I recommend you to google info about relays. Let me specify that I have never built this circuit myself and can't tell you how well it will work with a laser pointer.
ok, so i would build this entire circuit on a pcb or some sort of surface to facilitate soldering? What would be a good small size that everything would fit on? pretty soon ill head on over to modding once i get started
You don't have to make a PCB, you can simply buy a protoboard like this: http://www.futurlec.com/Pictures/PROTO777.jpg
yes, but I would have to purchase and mount all the other componemts on it. Do you have any good links to a place where I can buy most of this stuff in the US? I would go to circuit city, but i need some leds and some other little electronics stuff, so it wouldnt hurt to buy online.
yeah, but you could also use a shovel i said lol, how about those things that when you walk into a store they make make a ding sound to tell that someones walked in? use 3 of them but have the sound in your room?
lol ener you never fail to make me laugh. Where is the learning expericne to be had??? yo u know something that i dont, and i want to learn it. I can learn it by you teaching it to me. I want to learn how to use resistors and chips and stuff, and zwox and you are helping me. LOL of course i could use a shovel. But I will have a far better time doing it the hard way and learning OK new update on my lawn Wednesday evening i was "couched" someone dumped a sofa on my lawn and called my house, asking if i had a place to sit. They promptly told me to check my lawn. Anyway, we figured out who did it, and tonight, i went out with a friend and filled a van full of stuff. It included the orginal sofa 3 chairs, one wicker, one steel, and one wood(it had a leg broken off) one lamp/end table combo 2 upright vacuum cleaners 1 very large black briefcase 1 24" box fan 1 5 disk dvd player - we didnt test it 1 child's bicycle 1 shopping cart and thats about it, plus or minus a few small random objects. needless to say, we gave them a new living room on their front lawn, and tastefully decorated all their "new" furniture with spray paint.
well not really, we are just a bunch of highschoolers that do random stuff to each other. we provoked the couch because we deposited almost 200 rolls of toilet paper in their trees. So it is kindof a war that has been going on for almost a year, every month or so one of us will get some of our friends together and go have fun,and then they do the same, all in good fun with no harm intended. but anyway funkymunky, back to the origanal purpose of modding this, does anyone have any links to a place where i could buy most if not all of waht i need for a decent price?
i dont know much about electronics lol im not much help there, im just giving alternitives, if it was me i would of waterbined there house already lol, (if you dont know that that is then look is up lol), (ok its were you fill there wheely bin with water and lean it against there door, then when they open it they get watered lol)
While I do understand the joy of doing and learning, since I kind of do security for a living I figured I'd link what you're looking for to you Photoelectric Motion Sensor It'll just need a dc voltage supply and it will give you NC/NO to connect to whatever you want in the way of notification, of course I'd use the dry contact to run a relay switch on an autodialer for it to call my cell phone but that's just me Either way you need to set up a camcorder on a PIR so we can see thier face when you catch them :O Good luck!
hey. neat idea. heres some thing you might want to think about though. 1. you would need to use a class 1 or 2 laser. definitions here http://www.epanorama.net/documents/lights/laserclass.html anything more any it will be illegal 2. a laser beam is not parellel so you'll need to use a lens to make it parallel. if you dont by the time the beam reaches the LDR it will be about 5cm in dia. this one is just an idea but if you can, try and use two prisms rather than two mirrors. there smaller and more robust.
