Laser Trip Mine

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Introduction: Laser Trip Mine

This instructable will teach you how to make a laser trip mine.
If someone steps in the lasers path I have gotten it to set off a L.E.D., but you can make it set off other things.

You are going to need:

1. Laser.

2. Photocell, perferably a big one.

3. PNP switching transistor

4. 2 nine volts

5. potentiometer

6. L.E.D

*DONT POINT LASERS INTO PEOPLES OR ANIMALS EYES*

Step 1: The Laser

Attach the laser to the switch and the 9 volt. Make sure everything is compact so that later if you want you can put it in a box. Also to make sure the laser doesnt get burned use a resistor.

Step 2: The Circuit

First, you connect the negative side of the 9 volt to the emitter of the PNP transistor. Next, put the negative side of the L.E.D to the collector side of the PNP transistor. Then, attach one side of photocell to the base of the PNP transistor and the other side to positive side of the L.E.D. Finally, attach the positive side of the 9 volt to the left side of the potentiometer and the middle part of the potentiometer to the positive side of the L.E.D and the photocell. Make sure the potentiometer is set on low so you dont burn out the L.E.D.

The PNP transistor:
If you dont know which sides are what on the PNP transistor. Put the flat side North and the far left one emitter, middle is the base, and the far right one is collector.

To make it work:
Put the potentiometer on low so the L.E.D is totally off. Shine the laser directly on the photocell. When the laser is on the photocell turn the potentiometer slowly till it turns on, once its on turn it until it has just gone off, so it should be only a little to the opposite direction. Then to test it works put your hand through the laser and if the L.E.D turns on(should be brightly) then you've finished the project. If it doesnt make sure when the laser is on it the L.E.D is only barely off. Try to experiment with buzzers, relays, and other stuff.


If anyone knows Circuit and breadboard design software so I can make it easier to visualize the curcuit comment me. And if you have any questions or problems comment me.

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    96 Discussions

    Currently, I'm wondering if this can be adapted to an optical signal for a data I/O input or output, if so, then I'd like to know how because I'm researching into designing remakes of circuits and changing them into optical. For the power lines I'm thinking of using an led that uses uv light to small solar panel at the end since optical uses little electricity, I believe it's doable. I'm a beginner in this field so any advice would be welcome. I've got many ideas for it.

    So basically when the laser loses contact with the photoresistor it supplies power to the LED? That means you could wire in anything that ran on a nine-volt. Please correct me if I am wrong.

    Can someone give me the PNP transistor number like for NPN we have 2N2222 or 2N3904.

    1 reply

    Sorry, no. You need a laser BURNER to make it at least cut through paper. I know there has been some confusion about that....

    Laser readers like DVD ones read tiny bumps in the CD/DVD. The burner makes those bumps.

    Can you make some schematics for this?

    I tried hooking this up to a buzzer, but It isn't working at all. Please if anybody has any advice I'd like to know

    4 replies

    Most buzzers will not just work because they have electricity flowing through them, in fact if you were to open something like say... The Operation game you would find that the buzzer will usually even have a transistor of its own.

     you should try this instructable if you want a buzzer I am building one and it works except it won't stay on when tripped, so I am in the process of finding a different type of transistor.

    Google set reset transistor then either get the buzzer to run of the maximum (~5v) or use a relay type thing, to up the voltage

    I actually figured out u need a relay to get it to stay on after activation.

    is it pnp or npn?? cuz for most switichng applications ppl use npn

    Do you need the potentiometer? I can't seem to find one so if it wasn't there I wouldn't mind.

    1 reply

     Yes, it affects the sensitivity of the photocell, basically it is a variable resistor. You can find one at tri-state electronics on northwest highway in mt propect illinois if you around cook county (Chicago-land).