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How to Build Your Own Ultraviolet UV LED (Black Light) Flashlight

Updated on September 11, 2013

Safety Precautions

Work in a well ventilated area. Solder fumes are no fun.

Wear safety glasses.

UV light can be dangerous. DO NOT look directly into the lit LEDs. Don't shine the light in the eyes of others.

Very Simple Electronics

In Middle School I took some kind of shop class that consisted of 6 weeks of electronics. All I remember from the class is that I built some sort of "any idiot can do this" radio that didn't work. Obviously I was the exception to the rule.

Looking back, I'm pretty sure I know what I did wrong. It was something so simple that the teacher should have been able to spot it and the project would have been salvaged in a minute or less. I'm pretty sure I had a diode backwards.

Diodes and LEDs

The simplest description of a diode is that it acts as a 1-way gate for current. While there are many sizes and types of diodes, they all perform this basic function. If current is sent from the positive to negative poles of the diode, it flows. If it's sent from negative to positive, current doesn't flow. A diode's negative end is marked with a stripe around its barrel.

LED stands for Light Emitting Diode. LEDs are simply diodes that light up when current flows through them. Since they aren't cylindrical like most diodes, the positive and negative poles are marked differently. The positive pole of an LED has a longer leg than the negative.

Resistors

Resistors simply resist current flow. In actual application, they drop the amount of current flowing through a circuit. In our simple circuit they are merely there to drop the power down so that the 9 volt DC battery we're powering the flashlight with won't burn up the LEDs. The stripes on the resistor tell what its resistance is. We won't bother with learning to read them for this simple project.

Tools you'll need

Soldering Iron

Solder (resin core)

Drill

Drill Bits

Side Cutters (dikes)

Small Needlenose Pliers

Phillips Screwdriver #1 bit size

Hot Glue Gun with Glue

Lots of bad, blurry pics. Sorry.

I'm either at a rave or playing with an Ultraviolet flashlight in the dark.  Miles from town.  Where nobody can hear you scream.
I'm either at a rave or playing with an Ultraviolet flashlight in the dark. Miles from town. Where nobody can hear you scream. | Source
In addition to the positive leg being longer, it's also got the smaller part of the element attached inside the plastic.
In addition to the positive leg being longer, it's also got the smaller part of the element attached inside the plastic. | Source
Longer leg = +  Shorter leg = -
Longer leg = + Shorter leg = - | Source
Resistors.  They can be installed any which way, there is no polarity, no + or - with these guys.
Resistors. They can be installed any which way, there is no polarity, no + or - with these guys. | Source
LED with resistor attached.
LED with resistor attached. | Source
The pushbutton.
The pushbutton. | Source
The Box.
The Box. | Source
LED with - lead clipped, tinned, and bent 90-ish degrees.  The + lead has the resistor soldered to it already.
LED with - lead clipped, tinned, and bent 90-ish degrees. The + lead has the resistor soldered to it already. | Source
End of the box, drilled with a pair of LEDs ready to solder.  You are soldering the - end of the one with the resistor to the + end of the other.  Thus the pair's positive end has a resistor and negative end is just a lead.
End of the box, drilled with a pair of LEDs ready to solder. You are soldering the - end of the one with the resistor to the + end of the other. Thus the pair's positive end has a resistor and negative end is just a lead. | Source
Same pair from the side so you can see how they're soldered.  Very little visible solder, but it's a strong joint.
Same pair from the side so you can see how they're soldered. Very little visible solder, but it's a strong joint. | Source
Soldering the lead across the - side.  See that the + side (with resistors) is already done.
Soldering the lead across the - side. See that the + side (with resistors) is already done. | Source
Everything installed.  See how I've put the button right up against the + side so I could solder it directly.  The negative side is connected by the black wire from the battery connector.  The + side from the connector goes to the other lead on the b
Everything installed. See how I've put the button right up against the + side so I could solder it directly. The negative side is connected by the black wire from the battery connector. The + side from the connector goes to the other lead on the b | Source
Testing everything prior to gluing.  I won't show you the glue.  It's ugly.  I do believe in lots of glue.  If this thing breaks, you could pry the glue loose and fix it, but I'll probably just throw it away.
Testing everything prior to gluing. I won't show you the glue. It's ugly. I do believe in lots of glue. If this thing breaks, you could pry the glue loose and fix it, but I'll probably just throw it away. | Source
The finished product.
The finished product. | Source
The finished product being used.
The finished product being used. | Source

Parts You'll Need

I built some of these flashlights as a project for work. We got all of our parts from Allied Electronics. Any electronics warehouse will have similar parts. While Radio Shack doesn't stock Ultraviolet LEDs, they do have a range of normal colors if you want to build a different color..

LEDs, Qty 6, Mfr. Part: VAOL-5GUVOT4, Allied Stock: 398-0973. These are 5mm, "through hole," clear lens, Ultraviolet LEDs. Through hole means they can be mounted flat against a circuit board. Most LEDs are this design.

RESISTORS, Qty 3, Mfr. Part: CF-25-151-JTW, Allied Stock: 840-0078. These are 150 Ohm carbon film resistors with radial leads. Radial leads means that the resistor has wires coming out of each end of its cylindrical body.

PUSHBUTTON, Qty 1, Mfr. Part: 30-101, Allied Stock: 948-0321. This is a "normally open" switch. When you push the button down, it makes a complete circuit. If it's released, it's open and no current flows.

BOX ENCLOSURE, Qty 1, Mfg. Part: 40-12-9V-R-GL, Allied Stock: 278-0033. This is simply a black box with a battery compartment for a 9 Volt DC battery. It includes the connector and wiring to hook the battery to the simple circuit you're going to build.

WIRE. While I didn't use any wire other than that which came with the box enclosure, some 18 or 20 gauge wire is useful. It's also great to practice your soldering on before moving up to components.

How to Solder

The simplest thing to solder is scrap wire. First practice stripping the plastic coating off of the wire. You only want about 1/4" of the wire exposed. If you strip too much, it can always be trimmed later.

The first step in soldering is to "tin" the parts you are going to solder. Tinning is simply applying solder to each part before you try to put them together. Let your soldering iron warm up. Test it with the solder to see if it's warm. If the solder quickly melts when it touches the tip or the iron, it's time to solder. I keep my soldering station set to about 650 degrees F.

Touch the tip of the iron to the wire. Hold for about 3 seconds. Now apply the solder to the wire (not to the tip of the soldering iron). If the wire is warm enough the solder will be drawn into it. Once you've tinned a few pieces of wire, try to solder them together. Hold two tinned ends together and apply the tip of the soldering iron. The solder from the two ends should remelt and flow together. You need to apply a bit more solder with larger wires. With the components we're working with, you'll need very little extra solder.

While it sounds like you need 4 hands, the guy who trained me would hold the two ends of the wire in one hand and the soldering iron in the other. He'd have the spool of wire on a table with an end sticking up. Put the iron to the wires, one they're warm move down to the end of solder sticking up. Voila, you've got it. I'm not that nimble, so you'll often find me with a soldering iron sticking out of my mouth. I don't recommend that, though. It's just what works for me.

Get Ready, Go.

I find it easiest to do everything assembly-line fashion. Lay out your LEDs, push button, resistors, and wiring harness for the battery. Tin all legs of the components and the ends of the harness as well as the legs of the button. The wires on the harness are pre-tinned, but you want to be sure that the solder you're using sticks well to the components, so I always resolder them.

Clip the leads on the resistors so they have one long lead and one lead about 1/4" long. Take three of the LEDs and clip the longer lead so that they're about 1/4" long. Solder the short lead of the resistor to the short lead of the LED. You should now have three LEDs with a resistor for one leg. The longer lead is the positive side of the diode, so the resistance is on the side where the power has to flow for the diode to activate.

Now take the other three LEDs and clip the long leads so that they're about 1/4" long. Set all of the electronic components aside and grab the box and your drill.

You'll want to figure out how you want to mount the LEDs. I put one pair in the middle of the box front and the other two pair spaced out about 1/8" away on either side. The spacing really doesn't matter except they do need to be in pairs. Once you think you have it measured out, mark and drill. Drill with small drill bits and go up slowly in size until the LED sticks through, but won't fall through.

I used either a roll of tape or the solder roll as a work stand at this stage. Put the front that you've drilled over your roll of solder. Bend the six 1/4" legs on the LEDs so they stick straight out. Basically it should be about 90 degrees. Put one pair of the LEDs (one with a resistor, one without) in a pair of the holes so that the two bent legs point toward each other. Solder the two bent legs together. You can pull them out and do the next two pair. Be sure and put each pair in their correct holes. If your drilling was a bit off, each pair will have slightly different spacing.

Put all three pair back in with the resistors all on the same side. Bend the leg of one of the end resistors 90 degrees so that it crosses the other two resistors. Solder the bent leg to the two other resistor's legs. Clip the excess legs to where they're about even with the crossing leg.

On the other side, bend one of the legs off of the LED across the other two legs. Solder them together and clip the ends like you just did on the resistor side.

Solder the black battery lead to the non-resistor side. Clip a battery to the end and touch the red wire to the resistor-side wire. It doesn't matter where. Since this is a parallel circuit, the current flow is the same everywhere. All 6 LEDs should light. If they don't, check your solder joints and be sure that everything's still connected.

If nothing lights, flip the battery around and touch it to the connector (yes, backwards). Do they light? If so, you've got the LEDs in backwards. I built about 40 of these this week and I did end up with one pair backwards and one bad solder joint on the battery connector (so not mine, thank goodness).

Ok, remove the battery and set it aside if everything's working ok. Put the end of the box with the LED assembly you just made into the box. What you want to do is mark a spot to drill the hole for the button. What I did was simply solder one of the button contacts directly to the wire running across the resistors. If you prefer, you can solder a wire from one terminal to the resistor-side wire.

Drill the hole, pop the button in (and no, it won't be that simple), solder one contact to the resistor side (or a wire between the two) and then solder the red wire from the battery connector to the other lead of the button. Hook the battery back up and test again. Everything ok? You're done. If not, check your solder joints again.

Soldering takes time and practice. "The bigger the blob, the better the job" is not the truth. It shouldn't take a whole lot of solder to get the job done. At the beginning, you'll use more. As you get more confident and experienced, you'll use less. Also, a tip to test your soldering is to solder two wires together. Pull hard. The joint should not give. If you're using really light gauge wire, it should break, but not at the solder joint. The solder joint will be the strongest part of the wire if done correctly.

The final thing I did was glob a ton of hot glue over everything. This will hold all of your LEDs and the button in place as well as holding the solder joints together if the flashlight gets dropped. Don't glue yourself. It's hot glue.

Position the battery and wires so you can finish assembling the box without crimping the wires. Screw the case together with the provided screws. You're done. You now have a flashlight you can play CSI: YOU with.

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    • SantaCruz profile image

      SantaCruz 5 years ago from Santa Cruz, CA

      Awesome tutorial! I found you through the Hub Hopper. What a pleasant surprise :).

    • DougBerry profile image
      Author

      DougBerry 5 years ago from Abilene, TX

      Thanks. I spent a ton of time building these this week, so I thought I'd share. I didn't want to put a schematic in for fear it would scare people. Basically make it look more complicated than it really is.

    • Liz Green Berry profile image

      Liz Green Berry 5 years ago from TX

      (words words words awesome picture of you having a lightswitch rave words words more words.)

      Another brilliant hub, I'm sure.

    • KrystalD profile image

      KrystalD 5 years ago from Los Angeles

      Excellent! I would love to try this with my students!

    • RetailRich profile image

      RetailRich 5 years ago

      Nice job, and very interesting.

    • profile image

      varun sharda 3 years ago

      u r my new god!!!!! thanku soo much.....!!

      that worked like a charm....thumbs up!!

      excellent!!!

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