In this instructables, I have developed detailed instructions to build a USB rechargeable defense laser. I came up with this idea to protect myself from the rodents (possums and racoons) that live in my area as well as for self defense when hiking. The laser could actually do permanent damage to eyesight, and therefore is NOT A TOY.

Note: Another good use for this i'ble would be to use a less powerful laser and use it as a laser pointer for giving power point presentations. My fiance works in an office environment and says that laser pointers dying in the middle of presentations is a fairly common problem. This way you could make sure your pointer was charged on your laptop before giving the presentation.

In order to complete the project you will need the following materials:

- 1 usb drive
- 1 3V, 250 mA laser diode (can be obtained from 16x or faster dvd burner)
- 1 125mAh lithium ion battery (i got mine from a bluetooth headset, easy to find in a dumpster behind an office store, free with new cell phones, or super cheap at thrift stores)
- 2.8 Ohm resistor
- 50 Ohm resistor
- 1 ft copper wire
- solder
- 1 0.5"x05"x0.25" block of plastic (I used delrin)
- heat shrink
- CR2032 battery (only needed for testing)

You will also need the following tools:
- soldering iron
- pliers
- sponge
- hand drill
- 0.175" drill bit
- small file
- thread tap

Step 1: Find USB Drive

You will need a USB drive with a solid case to hold the battery, switch, focus lense, and laser diode. The one I used has an aluminum case.

(1) Disassemble the flash drive. Most USB flash drive split apart in two leaving a bottom and top half of the case. I just pulled on the usb portion of the drive and the rest of the electronics came out. You will use both the USB connector and the casing for this instructables.

Step 2: Desolder USB Attachment

In order to use the USB, you will need to first desolder the connections to from the circuit board to the USB connector. The connector has 4 points of connection on Side A(positive/negative and D+/D-) and 2 points on Side B(case ground).

You will need a soldering iron, solder, copper wire, pliers, and a wet sponge.

(1) I found it works best to add clean solder to the soldering iron, then clean it with a wet sponge(while hot).

(2) Heat the individual solder points, letting the solder absorb onto the iron or onto copper wire. In this manner you can break the connection points.

(3) Once you have the solder removed, the USB connector should easily fall away from the board.

Step 3: Make Your USB Connector Holder

In this step you will be making your USB connector holder. If the case to your USB drive has a built in holder, or the case itself holds the connector, you can skip this step.

(1) First you will need some plastic, enough to surround the connector and hold it properly between the walls of your USB case. For my connector holder, I started with about a .5"x.5"x.25" block of Delrin plastic ( very nice to machine).

(2) Next you will drill a hole in the center of the block large enough to fit a small file, but small enough that you wont oversize the hole for your USB connector. I used a 0.175" drill bit, so I only had to file the hole lengthwise.

(3) Now that you have your hole drilled begin to file away the inside material for a proper fit.

(4) Next, use a larger more coarse file to remove the material from the outside of the block. (be sure to check your work often so to not
undersize your block, a good tight fit will keep your project together longer and make your USB laser easier to charge)

(5) You will want to use some epoxy to glue the USB connector in place (be sure to not get epoxy on the connector prongs, if you do, use some nail polish remover to clean off terminals)

NOTE- not all USB drives are the same, so you should make a quick sketch of what you want your connector holder to look like when finished. If it looks like it will work for yours, use my holder design. It made my connector very sturdy.

Step 4: Solder USB Connector Charging Leads

In this step you will solder your charging wires to the USB connector and solder a 50 ohm resistor to the positive wire.

(1) With your USB connector glued into the USB connector holder, locate the positive pin on the back side of the connector.

(2) Cut two small lengths of wire ( sometimes it is more easy to solder a long piece of wire and later cut it to length), remove the plastic shielding from both ends.

(3) You will want to tin the ends of the wires, this just means putting solder on the ends before you solder the connection

(4) Apply heat with the soldering iron to the positive terminal, when the solder on the terminal is melted place the wire on it.

(5) Tin the ends of the 50 ohm resistor then connect it to the other end of the positive lead. (this resistor is used to limit the current going into the battery, without this, the battery could overheat)

(6) Now you are going to put some heat shrink over the open wire to shield other components from it. (I used a lighter to shrink this heat shrink, but be careful it happens fast. You can see this picture in the next step)

When you are all done, it should look similar to the pictures in this step.

Step 5: Installing the Battery

In this step you will be using epoxy to glue the battery in place, soldering the battery wires to the USB connector and installing a 2.8 ohm resistor.

(1) Take your battery and find the best location within your USB housing for it to be placed.

(2) Epoxy the battery in place. ( I glued the battery to the USB connector holder)

(3) Tin the positive lead of the battery and connect the other end of the 50 ohm resistor. (from step 4)

(4) At the joint of the positive battery lead and 50 ohm resistor, tin and connect the end of a 2.8 ohm resistor.

Step 6: Retrieve Your Laser Diode and Focus Lense

In this step you will be retrieving your laser diode. The following list is of things you should keep in mind.

(1) lasers can be very dangerous, this diode has the power to blind instantly, so never look into it or use it as a toy.

(2) You will want a laser diode from a DVD burner drive 16X or faster. ( this is just the power that I designed my project around, you could use other diodes, but you will need to use a different power circuit)

(3) You will find the focus lense with the laser on the laser carriage. ( when removing this don't scratch it)

(4) Lasers tend from static shock, so before you remove the diode, solder the terminals on the back of the diode.

Step 7: Laser Diode Housing

In this step you will be making a housing for the laser diode and the focus lense. I used a small block of aluminum about .5"x.5"x.25". You will also want to use aluminum because of it's ability to dissipate heat, making your laser last much longer.

(1) Find the location where you want the laser to exit the USB housing. (the light from my laser exits out the rear of the drive)

(2) Now that you know where you are going to be putting the laser, you will want to build a housing for it. Rough out the outside of the block to the general shape of the inside of the USB housing. ( I used a hand mill to rough the outside of my block, but a hand file will work fine, a good file removes metal very quickly)

(3) Now you are getting to the tricky part, you will need to drill two holes, one for the outside of the laser diode and one for the threaded lense adjustment. ( both holes will be in the same spot, but the hole for the laser case will be larger in size and shorter in depth than the hole for the focus lense, this will let the back side of your laser be flush with your laser housing) Your diode could very well be a different size than mine, so you will have to wait and see what you get for a laser to find out your drill size.

(4) Drill the second hole for the focus lense. This hole will need to be large enough for your set screw and your set screw will need to be large enough to hold the lense in the open side. ( I put my lense in a few different setscrews to find which one held it best, it ended up being a 6mm set screw) once I knew the size of the set screw I located the proper drill to make a 6mm tapped hole.

(5) Now that you have the two holes drilled, you will need to use your tap to make threads for the adjustment lense. (when doing this use some oil).

(6) File the edges and clean the housing before you put anything in it, you don't want to destroy your new laser diode or scratch the focus lense.

When you are all done, you should have something similar to the pictures I have.

Step 8: Wire in Laser and Switch

In this step you will be soldering the switch into your circuit with your laser diode.

(1) Now that your project is nearing an end, you can remove the solder from the laser diode ( this would be a good time to use some epoxy and glue it into the laser housing)

(2) To find which prongs are positive and negative, use the 3volt CR2032 battery (this battery does not have enough power to burn up your laser diode, so its a good way to play with your diode)

(3) With your laser diode de-soldered you will connect the ground side of the laser diode to both the USB ground and the battery ground (when you are done you can use epoxy on the connections to keep them from shorting out on other objects)

(4) Now you will be soldering the switch in, (you will probably be able to find one for free, I found one on the eject button of the dvd drive) I first stripped the ends of two short lengths of wire and tinned them. Next I soldered them to the switch. I then soldered the other ends of the wire, one to the positive end of the laser diode and the other to the 2.8 ohm resistor.

I placed my switch on the end of my laser diode housing, with this came a bit of filing, but it seemed to be a good location, you will have to see what is the best location for your USB laser.

Step 9: Final Step

Finally, put your laser assembly into it's casing.

You can charge the finished product either on a computer or a wall outlet usb charger. For this size battery, you should not charge it for more than about 5 hours.

(NEVER EVER EVER TURN ON THE LASER WHILE IT IS CHARGING, IT WILL KILL IT!!!)

Congrats on your new USB rechargeable laser!!!

Remember, this is seriously not a toy. Keep well of reach of children.

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