These cheapo pushbutton "closet lights" are everywhere, and--since they use tiny incandescent bulbs--are ridiculously outdated.
Since my last (first) Instructable ended up being absurdly expensive in retrospect, I decided to do this one on a budget of $25
NOTE: My versions of the first two parts almost certainly differ from what you'd get if you ordered those I've linked. I've had them for a while. However, I've tried to communicate the general methods that would allow you to do something similar.
Battery-Operated-Round-Closet-Light $7.50 or $0.50 (at flea market)
Cheap blinky RGB LEDs from ebay $8.50 /100 or $0.51 for 6
4-AA-Batteries $4.00 or 8.5 cents (for electricity to recharge 4 1.5V,1180mAh AA batteries at $0.12 /kWh)
Assorted header wires $2.50 / 20 or 12.5 cents for 1
Resistor(s) $0 (remove from other project or possibly not necessary)
Tape/Solder/Other Binders $0 (not strictly necessary)
Total Cost: $22.50 - Unused parts/discounts = $1.22
Cost goes up if you need to buy resistors from RadioShack. :P
Skip to the end to see the video!
Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.
Step 1: Open the Light !
Pretty straightforward, using a screwdriver remove the screws that hold the case together.
Put the screws somewhere safe. Step 6 is basically the reverse of this step.
Step 2: Investigate Innards and Break It
When you open the light, it's pretty easy to see how it works. There's a toggle switch connected to the battery leads at either end and a light bulb centered under the diffuser. The diffuser, when pressed, activates the toggle, and voila! the light turns on.
One lead of the light is connected to the positive terminal of the battery compartment, and the other is connected to negative through the switch.
If your light is like mine, and has an incandescent bulb, put the ageing thing out of its misery and cut the leads right now. Do it.
Step 3: Investigate Properties of Cheapo Blinky RGB LEDs
I stripped the wires coming from the switch, cut a header wire in half, and tied the ends to create a quick-connect quick-release power source with a built-in toggle button.
A bit of tape should be sufficient to hold the wires together, but if you're itching to use your soldering iron or want a stronger connection, go for it.
Being unsure of the color-changing LEDs' properties, I decided to use my breadboard to connect it to the ~6V power source through a reasonably large resistor (8.2k?) and measure the forward voltage drop.
This turned out to be impossible as it was constantly varying, but it said it was somewhere between 1 and 4 volts.
I decided to try two in series, which gave me much better results, especially when I briefly shorted one of them to ensure the colors turned on out-of-phase.
My LEDs ended up dropping around 2.6V each. If you end up purchasing the LEDs linked at the beginning of the article, the LEDs have a 3.2-3.4 V drop and will likely not work if you put two in series. At the very least, your blues will probably not turn on, as those LEDs require a larger forward voltage drop to operate.
Step 4: Plan Circuit for Reconstruction
Fortunately, I was taking these photos on a giant sketchpad, so I decided to use it for some simple calculations.
My "black-box" system of 2 LED thingies in series dropped around 5 Volts.
With a 6V supply and shooting for 20mA (common for LEDs), I needed a 50 Ohm resistor.
I just so happened to have a 56 Ohm resistor !
Now, I wanted more light than just these two, so I decided to chance putting 3 sets of these 2-series LEDs in parallel. Usually, you'd want to put a separate resistor (at 1/3 the resistance!) on each branch to ensure equivalent 20mA currents through all branches.
However, I was lazy, and--strangely--it appeared not to actually effect the brightness of the LEDs. There's clearly some black magick (like current regulation) going on inside these little components that I'm not entirely sure of, but they worked really well regardless.
I even found that they seemed to work without a resistor at all, but I left the resistor in, hoping it will prolong the LEDs' lifetimes.
***NOTE*** If you're using one of the LEDs from Ebay linked at the beginning of this Instructable, you'll want a 130-140 Ohm resistor. But don't take my word for it, use Ohm's law: Resistance = Voltage/Current
Remember, divide your final resistance by the number of parallel branches you have to help normalize current across the branches.
Step 5: Connect the Componets!
Make sure the LEDs are polarized correctly and join them together mechanically.
I did not solder these components together. Rather, I simply bent them carefully so they wouldn't break when I squeezed them together with my pliers.
One of my favorite ways to do this is to take a pair of pliers and pretend I'm a jewler working on precious metals. It takes longer, but is 22 times as fun! Take some time to consider the constraints of the simple circuit, and imagine how the LEDs are going to hit the diffuser. I enjoy a wabi-sabi aesthetic, as you'll see in the images below.
Step 6: Close It Up, Turn It On!
Thats it! Thanks for reading!
I hope you've learned that it's possible to make pretty blinky things without spending a lot of dough and also that electronics isn't always a perfect science. With a little curiosity and experimentation, you can figure out what you have and how to make it work.