henhen0412

hay crumlink i need to make a laser alarm for a school project but the circuit diagram here does not give the code for the trasistors can you give it to me or do you have a new design that i could follow please reply now

mneary

You can use any small signal transistors. Examples:

NPN: 2N3904, 2N2222, MMBT4401, BC547, BC847
PNP: 2N3906, 2N2907, MMBT4403, BC556, BC557

russianbadboylb

why dont people just modefy a nightlight?

Torben

Mains voltage isn't required to solve the problem, and night lights use mains voltage. Why mess with it if you don't have to? It's simpler to do using a photodiode or phototransistor, a transistor or two, and a 555, or even a microcontroller. Almost any microcontroller you could name would actually be serious overkill unless you wanted to add some features.

Other problems with using a night light:

• They're slow. Night lights use LDRs (light-dependent resistors) which have a response time which might be a problem, depending on the speed of the target.
• Designing your own, i.e. using a 555, lets you control more things, such as how long the alarm signal lasts. With a night light as the trigger, you would have to design a system (possibly using a 555) to control how long the alarm lasts. If you didn't, your buzzer would only buzz while the beam was actually interrupted. Somebody just walking through it would make it go "BZ" for less than a second. Using something like a 555 you could make it buzz for, say, 5 seconds.

While you could probably make a working alarm circuit from a night light, in short, it would be a) dangerous, and b) slow.


Torben

Gayan Soyza

If you look this thread you will get an idea about a LED night light.

http://www.electro-tech-online.com/e...ght-light.html

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Gayan
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