| Author | Message | ||
     nobody |
Im thinking about biulding a laser door alarm with a photo-transistor but i need help with the schematics. If you have any ideas or schematics post them here or send them to nobody@hotmail.com. Thanks, Jared | ||
| Simon Quellen Field (Sfield) |
Do a search on Google for "missing pulse detector". This is one of the better alarm circuits for what you are trying to do. You can also search for "laser burglar alarm". One such site is here. Others are here, and here. | ||
| Jared |
Here is one of my ideas. I was trying to think of a way for electricity to keep another circiut off.  | ||
| Jared |
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| Jared |
When the electricity stops due to the breaking of the laser beam, the electromagnet stops and allows the metal rod to drop. The metal rod then connects the buzzer circuit. | ||
| Simon Quellen Field (Sfield) |
That should work. Some improvements would be to use a missing pulse detector, so that someone can't defeat the lock by simply shining a flashlight at the photosensor. Second, a system where the buzzer is turned on by a transistor or an integrated circuit when the beam is broken, rather than turning off an electromagnet, will save batteries, since little power will be used in the normal case. In your design, the electromagnet is always using battery power, and the batteries won't last long. Books by Forest Mims can be found in libraries or at Radio Shack. They will show you how to do it. | ||
| Jared |
i dont really know about many electronics,so what is a transistor and what is a integrated circuit? | ||
| Anonymous |
COOL PALN | ||
| sciman |
????????????????im not sure if that would work????????????????????????????????? | ||
| Anonymous |
It could work, but if it did, the 1st 9-volt would drain in minutes. It's not the most energy-efficient circuit built. | ||
| Anonymous |
hey, im building an alarm using a lm555 integrated chip and a photoresistor, but the only problem im having is trying to reflecct the laser beam across a doorway with mirrors. Any ideas or help would be great, it's for a physiccs project. THANKS! | ||
| Anonymous |
I am trying to build a laser alarm, and I found this. I actually want to make one that fires a projectile at the door, like from a slingshot. | ||
| Anonymous |
awesome how are you planning on doing that? | ||
| Anonymous |
any idea how to reverse a photo resister so when you will shine lazer at it then it would be off?? | ||
| Simon Quellen Field (sfield) New member Username: sfield Post Number: 251 Registered: 12-2004 |
What you want is an inverter, such as the 74LC14 chip. | ||
| covenant_grunt_slayer Unregistered guest |
Missing pulse detectors: Are these common enough to find at a radio shack or a dick smith electronics store? | ||
| Simon Quellen Field (sfield) Senior Member Username: sfield Post Number: 295 Registered: 12-2004 |
You can build one using a 555 timer chip. Look it up on Google. Forrest Mims shows how in his books. | ||
| help u Unregistered guest Posted From: 207.69.136.198 |
in the laser door alarm the phototransistor did you mean a photodiode not transistor? email me with a responce and could you use a infared phototransistor? | ||
| Anonymous Posted From: 207.69.136.198 |
in the diagram wont the alarm stop as soon as the bean is back to being unbroken? | ||
| Austin Kirschenmann (Unregistered Guest) Unregistered guest Posted From: 4.246.231.115 |
What if you somehow made the magnet engange only when the beam is broken? This way it would use the 1st batt very little. A example might be to use a conducting spring pushing aginst the bottom part of the rod, only make it of plastic. (Just the bottom part) that way when engaged, the buzzer would stay on unil battery of the buzzer is removed, even if 1st battery runs out. Just a thought, I'm only 14  Hope it might help a little. |
