Do not underestimate the effort of desoldering and soldering, though. It took me about a day altogether to finish the project.
Step 1: What You Need
• 1 torch with 52 white LEDs, bought from eBay for 12 Euros, shipping included. I tried to get one with as much unused space inside as possible, and I was lucky. Maybe you can get a cheap one at your local electronics store and have it disassembled before buying.
• Given a 52 LED setting, I chose the following combination (all LEDs are of 5 mm diameter):
- 10 white LEDs (already included)
- 8 red LEDs
- 8 green LEDs
- 8 blue LEDs
- 9 infrared LEDs
- 9 ultraviolet LEDs
• With the chosen LEDs, I calculated the resistors needed (see next step) and bought:
- 4 resistors 1 Ohm, 0.5 Watts
- 1 resistor 12 Ohm, 0.5 Watts
- 1 resistor 5.6 Ohm, 0.5 Watts
- 9 resistors 27 Ohm, 0.5 Watts
• A rotary switch with 12 positions. You may get another one with less positions or use a totally different switch altogether.
• Isolated wire
• A small piece of circuit board for the 9 27 Ohm resistors
For tools I used:
• A 6.5 mm steel drill
• A dremel
• A soldering iron and some solder
• A glue gun
Step 2: Circuit Diagrams
As I intend to use the torch mainly with rechargeable batteries, I calculated the following circuit for 3.6 Volts, which is the typical voltage of three NiMH batteries.
Most LEDs could be set in parallel and driven with a single resistor, as they only use 20 mA current. My green LEDs need 30 mA, so I split them up in two groups with one resistor each. The infrared LEDs need a whopping 100 mA each, so I used a resistor for each of them.
Depending on the types and amounts of LEDs you are using, you may need different resistors. This LED resistor calculator may help you on your way.
Step 3: Inspecting the Torch
The circuit was laid out pretty simple and could easily be modified by cutting circuit paths and soldering additional wires.
Step 4: Preparing the Torch
With the shaft's position thus defined, the circuit would barely fit on top. To fit the switch inside low enough I had to carve away some of the plastic with a dremel.
Step 5: Unsoldering the White LEDs
Don't forget to leave some white LEDs on the circuit if you need them!
Step 6: Preparing the Circuit Board and Adding the LEDs
That done, I soldered the LEDs in. Except for the infrared LEDs, which are darker, all my LEDs have a clear housing so they look pretty much the same. Double-check the layout and the LEDs to avoid confusion here. Also remember to solder the LEDs in the correct polarity (flat side of the housing is ground).
As I had to cut a lot of plus lines, I finally had to solder some short pieces of wire to connect the plus lines within each group where needed.
Step 7: Adding the Switch and the Resistors
The 12 position switch has a small ring attached with a pin that can be placed into a series of holes, allowing to limit the switching positions. I used this to set the switch to the 6 positions that I needed.
To fix the switch within the torch head I used a glue gun which worked suprisingly well. Just be careful not to glue the shaft.
Finally I soldered the wires to the LED circuit board.
After reassembling the torch it showed that all LEDs were working perfectly!
Step 8: We're Done!
Of course your very own torch can differ in colours or design. You could use push-button switches to light multiple LED colours at once. You could even use RGB LEDs to save space. Let your imagination run wild.
Have fun and thank you for reading.