Introduction: Laser Trip Mine

Picture of 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


Step 1: The Laser

Picture of 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

Picture of 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.


DanielL19 (author)2015-02-18

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.

Dearden805 (author)2011-12-29

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.

lukeD (author)2011-07-13

I have a program for you, Yenka called. it is free if you take the home license. good luck.


amruth (author)2011-06-01

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

robot1398 (author)amruth2011-06-07

for 2n3904 its 2n3906

the "wow shammy" (author)2009-08-03

would a dvd player's laser work?

GameNox (author)the "wow shammy"2011-01-12

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.

ARJOON (author)GameNox2011-05-21

can i use a laser pointer

the "wow shammy" (author)GameNox2011-01-21

hard drives contain magnetic reading heads not lasers, right?

GameNox (author)the "wow shammy"2011-01-21

Yeah, I think so.

techno guy (author)2011-04-13

Can you make some schematics for this?

Sparklesam (author)2009-01-07

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

Cubie2 (author)Sparklesam2009-04-07

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.

Digy (author)Cubie22010-04-20

 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.

rrrmanion (author)Digy2010-10-31

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

Digy (author)rrrmanion2010-12-11

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

erveli (author)2010-11-20

How many ohms is the potentiometer?

coilsinamotor (author)2010-10-23

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

Young Genuis (author)2009-12-26

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

Digy (author)Young Genuis2010-04-20

 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).

minerug (author)2009-12-18

It would be better to get a B216 kit from Jaycar and hook it up to a relay, which in turn is hooked up to a siren or something 

Colonel88 (author)2009-10-26

Can you post a simple circuit diagram, like maxxxem's but just the bare bones approach?

maxxxem (author)2009-08-19

I modded your circuit a little to make LED light or 15 or 30 sec

Alex Palfreman-Brown (author)2007-07-09

Cool project. What rating is the resistor to protect the laser?

For my laser, i didnt have to have one. My laser worked on 4.5 volt first so i tried 9 volts and it worked but just as long as you can see the laser on a wall or the photocell the project will work. If the laser is powered with high amps it will burn the photocell and everything it comes in contact with so watch out.

Colonel88 (author)halo4564562009-08-17

that is a waste of energy.

pyro13 (author)halo4564562007-07-09

so how do u raise the amps??!?!?!

halo456456 (author)pyro132007-07-09

either a transformer or get power with high amps. there is an instructables that tells you how to do that

pyro13 (author)halo4564562007-07-09

ok can u please explain, for a dummy who knows nothing about electronics, how to turn a 5$ lazer pointer from walmart into something that can burn paper with minimal cost.

jman11 (author)pyro132009-07-18

go to and pick up a blue ray laser diode

halo456456 (author)pyro132007-07-09

ok, hmmm, have you search the 60$ Laser engraver/ cutter, if you have or dont want to you can take apart an adapter(like a one you plug it a wall, dont shock or kill yourself) that has around 3-6 volts and and 100-450 milliamps(mA= 0.001 so 100 mA equal 1 Amp). The adapter should say how much voltage and amperage it has. Heres a link that can explains it (if the link doesnt work here
hope that helps

cooter1974 (author)halo4564562007-08-16

halo456456, you have same misconceptions about basic electricity/electronics. I'm not saying that to offend you, but to try to get you to do some studying/research (example - 100mA does not equal 1amp, it equals .1amp) You can't take a power source and a fixed load and "increase the amps". You can increase the power source capacity, but it will deliver no more current than the load requires.

T3Hprogrammer (author)pyro132007-07-10


pyro13 (author)halo4564562007-07-09

whats it called?

halo456456 (author)pyro132007-07-09

60$ Laser engraver/cutter" by cgosh

jman11 (author)2009-07-18

do you think this would work for a multi stage coil gun?

santy22 (author)2009-04-26

put it into a HL laser tripmine papercraft and it would be VERY COOL

imakethings (author)2009-04-01

when the laser beam is tripped will the buzzer ring continuously?

PKTraceur (author)2009-02-19

try they have a PCB maker which you can order from them, and a schematic maker, which I use alll the time. It's free, and awesome. -RoAr

ian25 (author)2009-01-03

This is how I visualized the schematic. Hope it helps. Great Instructable.

sdaw (author)2008-12-10

could you just make a schematic using paint? it would be much easier to understand.

n0ukf (author)2008-11-18

You shouldn't need a laser for this, just a high intensity LED with a focusing (collimator) lens to focus the beam tightly. This won't be as tight a beam as laser, but then it'll give you a wider tolerance on aiming the beam at the photocell.

coopmister00 (author)2008-07-29

do u think this would work for a apintball mine?

halo456456 (author)coopmister002008-07-30

Um a paintball mine should use a trip wire which is mechanical. So to do all the adjustments would be really hard work.

coopmister00 (author)halo4564562008-07-30

actually i have an idea of how to make it work,replace the LED with a electro magnet... well i guess ill let u know if it works

something isn't working in the circuit:(

the LED isn't turning on.

twenglish1 (author)coopmister002008-09-06

check the polarity of the led

TheInventor (author)halo4564562008-07-31

No, actually it wouldn't be that hard if you knew what you were doing. I'm really good with electronics though, so it could be just me.

halo456456 (author)TheInventor2008-08-02

I'm not bad at this stuff, but others who want a quick working device this is simple.

About This Instructable




More by halo456456:Laser Trip MineWireless Power
Add instructable to: