Laser Trip Alarm

[o_DEATH_ANG3L_o]

Anyone ever do this? Sounds like it could be fun and useful. I would imagine a photocell would be involved and maybe a transistor. Any ideas?

 

[Cxrazy]

yeah, youd have to wire a transistor and a photocell somehow so that when there is no light (laser becomes blocked) a current is sent to  the alarm to trip it.....

Something like this might work:

Its a schem for a LED to turn on when the lights go off, but its the same basic principle if you were to wire the alarm to where the LED would be.

Helpful?

 

[turtlecannon]

The problem with that circuit is that the light will only be on while the path of the laser is being crossed. I've been working on a circuit for a laser alarm for a while that uses a 555 timer to make a buzzer go for 2 minutes after the beam is crossed.

 

[Rhith]

I have contemplated this before. Maybe even have it so that instead of an LED turning off, have it power a laser module that shines into some fiber optic circling your room so you can notice it more effectively if it trips. But wouldn't it only go off for the short moment as it is being tripped? I don't know too much about this so I'll just shut up. :-X

 

[Cxrazy]

I'm talking about having an alarm that would be turned on (like a siren or turn a stereo on, etc) when the light is off (laser is blocked)

It would be wired into where the LED would be placed. I'm sure it could be done somehow.

 

[Shilood]

Rhith has a valid point, in that the circuit interruption would cause a momentary current flow through the transistor. The alarm would have to have a latch circuit such that once turned on by current flow, it would remain in the ON state until it's preset timer ran through enough clock cycles.

 

[JECS]

this is basically the first project everyone does in gr10 electronics at my old highschool. door opens, wires touch completing the circuit, and an led is lit up. the led stays on after the alarm was triggered using a transistor.its basically 2 separate circuits both grounded but one doesnt receive flow till after the transistor is triggered, but instead of wires its a photoresistor and laser.

 

[Rhith]

Here are two little sections in this ten year old laser book I was reading.