This simple circuit creates an LED lantern that can sit on a desk or be hung outside. It consists of a curved circuit board, a few LEDs, and some resistors.
By adding a nine volt battery in the base and changing the circuit slightly, it can be made into a portable light source. See step 2.
Step 1: Materials
For etching curved circuit boards:
2 x-acto knives
Clear vinyl shelf lining from Walmart
12"x12" Thin Scissor cut copper clad fiberglass board from Electronic Goldmine:
000 or 0000 steel wool from hardware store
Krylon Crystal Clear Satin spray paint from hardware store
LEDs, Ferric Chloride and resistors from: http://www.mouser.com/
12 volt battery or 12 volt power supply
Step 2: How It Works
The lantern is designed to run off 12 volts, but can be easily converted to portable battery power. As is, It powers sets of four LEDs in series. A dropping resistor in series with the LEDs keeps the current through each led at 20ma or less. You can use any standard LEDs you want. But you will have to adjust the dropping resistor for every four LEDs as they vary in resistance depending on the color and size of the led. You can use any number of four LEDs wired in parallel as long as the total current does not exceed the carrying capacity of your power cord wires. For this project I chose four sets of four LEDs.
I chose to use PLCC2 surface mount LEDs to maintain the flat profile of the curved circuit board and because they are the easiest surface mount LEDs to solder that put out a bright light. I originally used four white LEDs which required a 68 ohm dropping resistor. Then I decided I wanted a bluer light and changed it to three whites and one blue. The extra resistance of the blue led meant that I didn't need any resistors to keep the current low so I put in some 1 ohm resistors mainly to show where the dropping resistors need to go in the circuit.
To convert to battery power you can install a nine volt battery in the base and remove one Led from each set so that only three LEDs are in series. The three white LEDs in series that I tested, ran at 14 ma without a dropping resistor at nine volts. With four sets of three LEDs in series, the total current is only about 56 ma.
Step 3: Curved Circuit Board Pattern
Pic3 shows the shape and dimensions of the single circuit board that is used for the lantern. I like to first make the pattern out of card board to test if the dimensions are right and it will bend in the right places.
The circuit board material is so thin (.007") that it can in fact be cut with ordinary scissors. You can hand sand the edges smoother if you like.
Two layers of vinyl shelf liner are placed sticky side in to sandwich the circuit board. This provides the resist for etching the board.
Pic4 shows the layout of where the vinyl will be cut out. I like to freehand sketch the cutouts in pencil, make any corrections necessary and then go over the lines with a sharpy.
Pic5 shows the pattern to be cut out on the back side.
Step 4: Etching the Curved Circuit Board
Cutting the Pattern
Pic5b shows how the vinyl shelf liner is cut with a double bladed knife and a thin long section is removed. This is done wherever you want the copper to be etched away.
Pic5c shows the double bladed knife which is easily made by bolting on two exact o knives on either side of 1/16" FR-4 circuit board material that has the copper etched off.
Etching the Board
Before etching the board in Ferric Chloride solution, the cut edges of vinyl should be burnished so the etchant cannot ooze under. I burnish by rubbing the rounded end of a Popsicle stick along the edges to make sure they adhere well. The whole thing can then be immersed in Ferric Chloride for about an hour at room temperature. Rinse the etched board very well with water before you peel off the vinyl shelf liner.
Cleaning the Board
Even with burnishing, some etchant will get under and stain the edges of the copper traces. I use the fine steel wool to polish away any stains or finger prints on the copper.
Step 5: Soldering the Circuit
Pic6 shows the etched board with LEDs and resistors soldered in place. It does not show the 30 gauge magnet wire soldered to the two bottom inside traces to provide power.
Pic7 shows a clamp I made out of spring metal to hold down surface mount components while soldering. Details on how to make the clamp are here:
Step 6: Bending the Circuit
The circuit can now be bent and soldered at the base. I recommend wearing latex gloves while bending the circuit board to its final shape. Fingerprints easily stain the polished copper.
The base is bent around to form a ring and soldered through a hole drilled into the end that goes on the inside of the base.
Step 7: Painting the Circuit
You can of course, leave the lantern unpainted and allow it to weather naturally. But I like the look of copper and chose to spray it with Krylon Crystal Clear Satin Spray Paint. This will keep it from darkening and allow it to be handled without getting finger prints all over it. It also prevents accidental shorting.
You could also cover the LEDs with bits of tape and then spray paint the whole thing a solid color. I tried a metallic silver on some scrap circuit board and it looked quite good.
Step 8: Possibilities
This curved circuit board is so thin, the final lantern is very light and only weighs about one gram. This allows it to be hung upside down on 30 gauge magnet wire. It could also be hung on a wall. The magnet wire is thin enough to run along the wall and make it virtually invisible by painting over it.
Because it runs on twelve volts there is no shock hazard and it can be hung outdoors.
Here is a link to a desk lamp I made using the same curved circuit board technique: