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In this instructable I will teach you how to build a discreet dual laser tripwire.

This is the receiving Unit only, as you can use any laser pointing devices mounted as you like.

I have created all of the 3d printed files for your unlimited use.

You will need some basic electronics skills and access to or have a 3d printer. (There are many online prototyping shops that will 3d print your model for you.)

This is a dual laser based perimeter defense system that can be used outside of your residence to create a perimeter to notify you if someone is too close to your home and to make a noise to let the intruder know that you are now aware of their presence. (Disclaimer, this is not a life saving device and is to be considered as a toy.)

It is different then the single laser tripwire that you see posted on Youtube. I've modified circuits after reviewing many online to a dual system so it won't trip by a leaf falling or a small animal or a bird crossing it's path. Once tripped you do have to hit the reset button.

Unlike many others it doesn't go on and off when something passes through it like the alarms when you walk through a convenience store.

Basically you use the same electronics so I will refer you to those videos, but I've made changes to add a secondary photocell and a potentiometer, so you can set it to alarm if only one or both lasers are triggered eliminating false alarms. If you look up do it yourself hacks, and see the laser tripwire from "Make", this is a modification of that circuit, however I've created a 3d printed housing and incorporated store bought parts to make this a highly stealthy apparatus.

I've modified the single system by introducing a potentiometer and a secondary photocell.

It's really not as hard as it looks and will cost you about $25 to $30 for parts.

The part numbers of the parts are the leading file numbers attached on the photos, but if instructables changes the name, I've included the numbers within these instructions.

I have included .stl files for your convenience along with jpg's and a video of the wiring circuit board, along with schematics and photos of the build I believe you will enjoy.

The companion build will come out later and will be a dual laser holder that is as stealthy as this thermometer receiving unit. Soon you will be able to look up Stealthy Laser Security for 3d printing.

This unit works well when you mount two separate lasers and aim them toward this receiving units photocells. So if you want to mount your lasers in a different lawn ornament, you are able to and then point those lasers at this unit.

Thank You for Looking at my instructable I'm sure this won't be my last project. RomeoThecla@yahoo.com

Step 1: First Grab These 3d Printer Files From Below

Mounting Bolts (print 2)

Photo Sensor Mounts (print 2)

Resized Threaded Round Nuts (print 2)

Bottom box of project (goes under outdoor thermometer)

Box Top (goes over top face of thermometer, it is a template for your holes that you will make through the thermometer face, you will toss this part when done or use it later to build additional thermometers)

Cap Spacers (print 2) these are to go over faceplate and under the threaded round nuts when building project.

Top Mount

Bottom Mount (this has bottom cuts so you can run a wire through the bottom or you could print two top mounts and flip it when using it as a mount)

Print Away!!! RomeoThecla@yahoo.com

Step 2: Get One of These Thermometers

It isn't necessary if you just printed the template file above called box top template for cutting , but if you want an inconspicuous alarm system, then go to Home Depot and get one of these Home Depot Thermometer model 00339 hd internet number 100659742 store sku 816799. They are usually less than $3.00.

Use the file above or that you printed from the last page and place it over your thermometer you just purchased and drill the holes from the template overlaid onto the thermometer.

Now you have a box cover that looks like it has been store bought. Look at images above to see where holes were cut using template. romeothecla@yahoo.com

Step 3: Parts Needed From Radio Shack or Mouser

Here are more parts you need to complete this project, I've included Radio Shack numbers, however you can find some of this stuff online through Ebay or other outlets. I've found all of these parts in the Radio Shack stores.

271-515 on/off laser sync, or potentiometer, basically a radio volume control on/off switch

274-0403 Control knob

275-003 Reset Switch, smt tact switch 12vdc

276-159 dual printed circuit board usually in stores

276-1657 Photocells

276-1718 Timer iC 555, you can get a ton of these off ebay too

2730060 Piezo Buzzer

2741583 Power Jack (with a positive center)

2711311 Resistor 100 ohm

4.5v power supply, just ebay it or Amazon it, you will find them, you may have one lying around

Questions: romeothecla@yahoo.com

Step 4: Circuit Board Diagram

Click on Image above for Circuit

If you've not utilized 555 circuits before, now is a good time to learn for little hobby projects.

Review video above so you know what you are doing and pause it when it comes to circuit board to see how pins are lined up and dry erase markers marked on board

First Print out copy of Circuit above

Second Lay out your parts on Circuit so you know where they all go

Third Hold your 3d printed part up to your parts so you know how long to cut wires for Switches and Photocells

Fourth Write the numbers of your pin outs from your 555 chip onto the backside of the board, when you place your chip on the board the numbers on the backside will be reversed your 1,2,3,4, pins will now be on the right side of the board and you pin outs 5,6,7,8 will now be on the left side, so be aware of this.

Fifth Populate your circuit board with the 555 chip, (You can solder on the wires going to the photosensors but don't solder the photosensors yet, just the lead wires going to the photo sensor mounts) solder in the 100 ohm resistor, about 2 inches of wire for your reset switch, your piezo buzzer, a wire from pin 4 to pin 8, use about 3 inches for your on/off switch, use about 5 inches for your 4.5 power jack, anyhow if you've done circuit boards before finish it off.

Notes: Be very careful soldering around the chip, what I did was used a chip holder from Radio Shack first, but the chip kept popping out, so I soldered it straight to the board. The chip is very minimal in price so if you damage it, you usually get a couple in a package or from Mouser, I believe I received piles of them for very minimal cost. You will connect the photo resistors to the leads during final assembly of box, don't mount them until you've completed every other aspect of mounting parts to the 3d printed housing. You will need a small jump wire from pin 4 to pin 8 on your circuit board. Questions? Romeothecla@yahoo.com

Step 5: Assembly

Alright you've made it up to this point....Congratulations!

Now it's time to assemble your box.

Grab your populated circuit board and place the reset switch in the little square on the bottom 3d printed housing.

Screw your circuit board in using 4 screws that you can find at any home depot or use a hot glue gun.

Grab your photosensors that should be not have been mounted yet as that will be our next part of assembly

Step 6: Finally Mounting the Sensors

Whew!!

By now you've probably put all the parts together without putting in the electronics to see fit and how it goes together. It's very simple as there are only 10 to 12 pieces of 3d printed parts.

Some of the parts may be extremely tight and hard to fit into the project as we are working in millimeters.

They may even need scaled by your printer to fit properly using the stl file slicer.

But here is a quick overview of what is needed to finish this build.

Your circuit board, potentiometer, voltage jack, reset switch, should be mounted into the bottom box by now.

Take your photo sensor leads and feed them through the threaded towers in the base of your model f you haven't done this already and solder the photosensors to the leads.

Place your photo resistors over the sensor mounts and pull the sensor along with the mount using the wires that you just pulled through the towers before soldering, and pull the wire along with the mount and the sensor down into the towers.

In the smaller hole above the large hole where you pushed the wires into the tower, secure the mount with a small screw, this will keep the photo resistors from sliding out.

Step 7: Thermometer Cover Assembly

Take the thermometer or cover template and place it over the two towers and over the lip of the bottom box.

Take the two caps and place them over the two protruding towers, so the larger deeper side faces the right side of the box.

Take the two round nuts and secure the thermometer onto the bottom box.

Step 8: Mounting to Outside Wall or Hallway

Take 3d printed Wall mounts and mount only the top mount using a small level and mount to wall.

Take Threaded Mount and mount it to the top of your Box and tighten but not overly.

Get your 2 lasers positioned and aim one at the bottom photo sensor and the top photosensor.

Now take your bottom wall mount and connect it to the bottom of the laser thermometer and then mount it to the wall.

Violla

Plug it in, adjust potentiometer. Test you lasers, sit back and let your family test it out for you, by surprising them with the alarm when they walk through it.

Above are photos of the next project "Stealty Laser Security for 3d printing" using the mounts included with this project.

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