The first thing we have to do is to remove the plastic lens from the flashlight. We do this for two reasons: First of all, you will probably have to remove it in order to get to the LEDs. The second is that plastic tends to diffuse and attenuate infrared energy. I pierced the lens with a sharp object and popped it out, as you can see in the following image:

Lens removed

As you can see, the LED assembly is now loose in the case. If we remove the assembly and turn it over, we can see how the LEDs are connected to the battery pack. The positive or anode end of the LED is connected to the center terminal of the pack while the negative or cathode end of the LED is connected to the case.

Rear view of PCB

OK, time to warm up the old soldering iron and have at it. What you have to do is basically remove all the LEDs from the PCB without damaging it. Fortunately, these flashlights are cheap, so you can buy a couple of flashlights depending on your confidence level.

Once you have all the diodes LED's removed, it is time to replace them with the infrared ones. If you're lucky, the LEDs you are installing will have a flat side on the case. This is the cathode or negative side of the LED and it should be soldered to the negative side of the PCB.

Some LEDs have one short lead and one long one. The short one is supposed to be the cathode, but I would highly advise checking to be sure. The following image shows how to check your LED using the diode setting on your multimeter. In my case, it is indicated by an image of a diode.

Finding the cathode with a meter

Checking an LED is like checking any other diode. With the negative lead of the meter connected to the cathode (short lead) and the positive lead connected to the anode (long lead), you should get the minimum reading of ohms.

Because LEDs do not behave like normal diodes, this test might not work. If you don't have a diode setting on your meter, just use the lowest ohm range. If you aren't sure, then the easiest thing to do is solder one LED and then temporarily reassemble the flashlight. If you cup your hands around the lens, you should see a faint red glow from the LED.

Finding the cathode

Now that you have the first one installed correctly, all you have to do is repeat the process for as many LEDs as you have. Once you have all of the LEDs installed, you should check the project by pointing the flashlight at a cheap black-and-white video camera. You should see the glow from the LEDs. One way to check if the camera will work is to point your TV remote at the camera and see if you can see the LED flash when you press a button on the remote.

Once you have tested your Special Ops flashlight, you should use 5 minute epoxy glue to hold the LED assembly in place.

Your finished flashlight will look much like the following image:

Finished flashlight

If you enjoyed this quick and hopefully easy project, there is another one similar to it in the following pages. Many of you have probably seen LED headlamps in camping and hardware stores. The following pages will show you how to modify one of these lamps in pretty much the same way as we did the flashlight.

If you're a nature lover rather than a weekend warrior, you might find this project useful because it will free your hands for your camera or binoculars.

The following image shows the headlamp that I used. Yours will probably look very much the same.

LED headlamp

We will be disassembling the headlamp in the same way as the flashlight. Simply turn the bezel until it comes out in your hands. Once again, we are talking about a $2.00 investment here so you might want to buy a couple, just in case you have to sacrifice a few in the name of science.

Lamp with lens removed

Once you remove the two small Philips screws, you can now remove the circuit board containing the LEDs. The headlamp I purchased came with a switch that allows you to have one, three, or all the LEDs on at the same time. I'm not sure how practical this is for our project, except possibly to conserve battery power.

PCB removed for modification

Now that you have the lamp apart, it is time to fire up the soldering iron and solder removal tool and go to it. As in the previous project, simply replace the white LEDs with IR ones and off you go.

The cool thing about this lamp is the LED selector switch that allows you to turn on one, three, or all LEDs. If you are going to use it for nature observation, you could build yourself a lamp with three red LEDs and four white ones. That way, you can move about with the red LEDs and not ruin your night vision, unless you see something interesting.

This chapter contained two hopefully simple projects that allowed you to blow the dust off or enhance your soldering and desoldering skills. These skills will come in handy in the chapters to follow. We built two inexpensive but useful projects. All for about $5.00 per project, depending on how much the LEDs cost you.

Use your imagination. How about blue LEDs and wearing the lamp on your chest or head for Halloween?

In the next few chapters, your soldering and construction skills will be challenged even further, as we build a motion sensor out of a piece of a water pipe and a flashing infrared beacon. So read on.