UltraViolet LED Bug Zapper

There's High Voltage in Here!
remember this:

1: There can be high voltage when it's unplugged, or even when it's off!
     Build a shorting rod of some sorts. I used a bamboo skewer and put a couple inches of Aluminum tape at the end. I tap it against the screen to see if it's hot, and also to short it out after I shut it off again.

2: Remove the battery leads, and make sure they don't accidentally touch the battery contacts again. But you will have to power it up sometime...

3: Be Careful! This stuff can hurt you. Even if the voltage itself doesn't cause real harm, and it might, you could get hurt by falling off the chair or hitting your arm against something as it snaps back. NO FUN. Don't play with things you shouldn't.

The LEDs are powered from a 6 volt battery that's inside the unit, the big black box there. Other battery powered Zappers might use a different voltage like 12 volts so you will need to adjust the resistor and wiring accordingly. If there's no DC power source already in the unit, then it might be difficult to add.

It's easy to wire the ultraviolet LEDs off of 6 volts with a dropping resistor in series. In my zapper the ON/OFF switch was down by the battery, and the switched power then went to the circuit board at the top. I figured I can put two UV LEDs at each end of where the old Fluorescent tube was, for a total of 4, driven off the same wire carrying the 6 volts to the circuit board.

We got our Ultraviolet LEDs from Radio Shack, convenient and affordable!
Here's what to ask for.  I used a total of four so get at least two packs.
5mm High-Brightness Ultraviolet LED (2-Pack) $1.69
Model: 276-014 | Catalog #: 276-014

Not all stores will have them, so you can call ahead first, or check online at this address.


These are like "standard" LEDs in that the negative lead is the shorter one, has the flat-side of the LED body next to it, and also is connected to the larger piece of metal you can see inside the LED body itself.
an instructable is worth a thousand words (?)

I was able to use the same connector from the fluorescent tube to hold the two LEDs on each end. I simply cut the leads a bit, then bent them appropriately, getting the polarities correct. I connected them in parallel, negative to negative, and positive to positive, and angled away from each other a bit.

I want to run these LEDs at 20milliAmps each from a power supply of 6 volts and the LED forward bias voltage should be about 2.8volts.
(6v - 2.8v) / 20mA = 180 ohms for the dropping resistor in series with the LED.

But, since we have two LEDs in parallel, we need to double that 20mA to 40mA total. So to let more current flow we cut that resistor by half to 80 Ohms or so.

NOTE: It is really not 'proper' to connect two LEDs in parallel with only one dropping resistor since they might suck up slightly different currents because of device differences. the total might be 40mA for both LEDs, as designed, but one might be getting 22mA while the other is only getting 18mA. It's better to build in one resistor for each LED, but, this was easier then mounting two resistors in there and they don't have to be the exact same brightness anyway...

I happen to have some 67 Ohm resistors around, so I used those. You can measure the voltage across the resistor when it's powering the LEDs to calculate the current flowing through both the LEDs.
In my case i measured 3.2volts across the resistor of 67Ohms.
3.2v / 67 ohms = 48mA
so approximately 24mA per LED.

Remember which lead is Positive or Negative!

Next: How to reflect the UV light

I looked around my shack and noticed some clear, 1/2" plastic tubing laying around. Since this is about the same diameter as the old fluorescent tube it can occupy the same space nicely, and it's just wide enough for the two LEDs, side-by-side at either end.

I hooked up the LEDs to a power supply and resistor for testing first and you can see quite a clear spot coming out it, probably 6" wide at a 12" distance.

NOTE: you can use a white T-shirt to see the beam. Anything white that was recently bleached or at least cleaned would be good. The chlorine in the bleach really shows up the Ultraviolet light nicely.

Now, both pairs of LEDs are pointing at each other, inside the tube. But the light can still shoot through the tube as a beam.
So, to cause the light to bounce all around and not just in one direction I simply sanded the outside of the clear tubing to make it "frosted". This seemed to work well enough. I don't think this type of tubing absorbs UV very much. most of it should go right through it.

Then i mounted the tube and 2 connector assembly back into the Zapper just the way it used to be.

In the first picture you can see I reassembled the "replacement bulb" just like it was when I found it, but now the leads connect to the 4 ultraviolet LEDs (2 on each end) and not an expensive and short-lived fluorescent tube.
You can also see the 67 Ohm resistor I soldered on to the Blue ground wire in my particular Bug Zapper. It doesn't matter if the resistor is on the Positive leg or negative leg in this situation.
Next i'll solder the negative wire coming from the LEDs to the resistor and then i'll solder the positive lead to the Brown wire, which in my zapper comes from the switch after coming off the batterie's 6 volt positive terminal.

The second pic show the same thing going on at the top of the zapper.

Then, I reassembled everything carefully. Taking pictures can help you remember how these things go back together....

My father did this one before I did mine. The case on this type of zapper wasn't easy to open up so he worked from the bottom only. instead of a clear plastic tube he used a piece of wood dowel about 1/2" in diameter and stapled some 14 to 12 gauge wire along the lengths of the dowel, one wire for the positive 6 volts and one for the ground.
This is sort of visible in the second picture.
Then he soldered the LED leads to these wires right on the dowel, and bent them into position, pointing outwards.
it seems to work very well, there are many more mosquitos in his neighborhood than mine!