Proj1: Hanging Lantern Tutorial

This is a small tutorial on how to build a small lantern for decorative purposes. This small  lantern works on a weight activated switch. So in essence you can simply hang the lantern and it will light up, and turn off once you un-hang it. This is a nice little idea that can be applied to several different containers (as long as they are heavy enough) and can make a nice little addition of lights/lanterns in several different places. Since its winter, Id like to see a bunch hung on the branches of trees.

Materials:

4- Green LEDs (Mine were 2V)
1- Battery Lead
1- Thin conductive wire roll
1- Soldering Material roll
1- 9V Battery
1- Krazy Glue
1- Needle Nose Pliers
1- Wire Cutters
1- Electrical Tape roll
1- Sugar Dispenser
1- Pack of plastic coated Paper Clips
1- Small Rubber Band
1- 56 Ohm Resistor (I used 5×10 Ohm Resistors)
1- Pack of Colored Foam Sheets
1- Pair of Scissors
1- Soldering Gun

The Diagrams:

Figure 1 shows a simplified view of the circuit we are building. Its a simple circuit of 4 LEDs hooked up in series.

Figure 2 shows a more applied diagram. You will notice that the battery is shown, along with the strips of colored foam (in gray) that will hold the circuit together. This is to get an idea how everything fits together. The switch will actually be attached to the bottom part of the lid on the sugar dispenser.

Part 1: Getting the Foam Ready

You will need to cut the colored foam (your choice of color, just match the LED color) into three  4″x1″ strips. Basically you’re going to need 2 strips to go along the inside in kind of a ring fashion and 1 strip to go vertically inside of your Sugar Dispenser. Depending on the size of your particular Sugar Dispenser you may need to alter the measurements. 

You want one strip to go vertically from the very bottom of your dispenser all the way to the top. The other two, you want the length to go around horizontally forming a ring along the inside of your dispenser. These should not be full closed rings, you should allow a 1″ space for the vertical strip to fit into. Just keep that in mind.

Now you need to put some electrical tape on one of the sides of the two strips that will form the “rings” inside the dispenser. Although you are working with very low voltages, I always llike to be safe.

Part 2: Some Quick Math

Looking at the circuit diagram, we are going to be building a circuit of 4 LEDs in series. We need to follow our basic Ohms Law R= (V1-V2)/I. In this case our power supply is V1=9V , the total voltage drop across each LED is V2=8V, and the LED current is 20mAmps. Set up in the formula: R= (9V-8V)/20maA. Which leads to our Resistance needing to be:

R= 50 Ohms or the nearest higher rated resistor 56 Ohms.
Here is a handy online LED Calculator to help you out with these values: http://ledcalc.com/

Due to the resources available to me, I had 5x 10Ohm Resistors which I needed to solder together to make one 50 Ohm Resistor. 

Part 3: Soldering & Such

We are basically building one long circuit of 4 LEDs and 1 resistor in series. So looking at our design, were going to have 2 LEDs at the bottom and 2 at the top inside of our Sugar Dispenser.

First, you want to solder together 2 LEDs together, using about 1″ or 1.5″ piece of conductive wire, making 2 pairs out of the 4 LEDs. After youve successfully soldered the LEDs together, you want to solder a piece of conductive wire to a free end of an LED on each pair. So, to clarify, you will have two attached LEDs then one free end (no wire) and one end with a piece of wire. You want to make the wire about 4″ in length. This wire will be the way the bottom LEDs connect to the top, and then the top LEDs connect to the switch on the cap of our Sugar Dispenser.

Optional: Due to the resources available to me, I had 5x 10Ohm Resistors which I needed to solder together to make one 50 Ohm Resistor. 

If you think you’ll need a little more leeway on the leads of the power supply, now is a good time to solder about 2″ worth of conductive wire to the leads on the power supply.

Part 4: Building the Circuit

The first thing you want to do is to attach each pair of LEDs to a strip of the colored foam using electrical tape. Its very important that you keep in mind the design of the circuit and make sure that you follow the design. You want to make sure that the long wires end up on opposite ends of the strips. You also want to make sure that the piece that you designate to be for the bottom has the LEDs pointing towards the ‘top’ and the piece that you choose to be for the top has the LEDs pointing towards the ‘bottom’.  Pro-tip: label each side of the foam as positive (+) or negative (-) according to the polarity of the attached LEDs.

Now you want to attach the leads of the power supply (disconnect the battery first!) to the third piece of colored foam with electrical tape. If you want, you can label the positive and negative sides or you can follow the typical red=positive black=negative. Now you want to solder the positive lead of the power supply to the positive end of the LED on your top piece of colored foam.

Lastly, just connect the negative lead of the LED (on the top piece of foam) to the positive lead of the LED on the bottom piece of foam.

Part 5: Making the Switch

Keeping in mind that this will be a switch that is activated by the weight of the lantern, we will construct the switch to close on weight and open through a spring/rubber band mechanism.

First trace out a circle on a piece of colored foam using the cap of the Sugar Dispenser. Then simply cut it out using your scissors. Take your lid and using the needle nose plyers, carefully remove the little flap that lets the sugar out of the dispenser. Now place the circle you cut out inside of the cap and puncture a hole through the hole on the lid (this is where the sugar would normally come out from). Now place a piece of electrical tape over the hole you made on one side (this will be the side that holds the circuit switch) and punch the hole through that too.  Its easier to pierce through each material individually rather than at the same time.

Next, you can use the wire cutters to cut a small “U” shaped piece of a paper clip. This will be used to anchor the rubber band to the foam. You then take your small rubber band and loop it around the little u-shaped piece of the paper clip. Then simply super glue it on the colored foam about an inch away from the hole you made. Play around with it, keep in mind the rubber band needs to stretch very close to the hole you made once the weight of the lantern is hung from it. Super glue this piece of foam in place on the inside of the lid of the Sugar Dispenser.

Now you want to take a paper clip and make it straight except for the small u-shaped loop and bend it around a pencil twice. You can cut off any excess paper clip. It should leave you with a small hook with a loop on it. Take your wire strippers and take off the plastic coating off the loop end of the paper clip (you just bent) and off the small u-shaped loop as well.

With that done, you can now solder the wire that leads to the resistor to the u-shaped loop/hook. Once this is done, you can super glue the looped end to the electrical tape on the colored foam.
 

Now it gets a little tricky here. You take another paper clip and stretch it out. You make a small u-shaped hook on both ends of it. Somewhere just above one of the hooks you want to strip the plastic casing off. Then you want to solder the negative lead of the power supply to it. Then you want loop the rubber band with the hook and close it. Now you stick the rest of the paper clip throught the hole you punctured on the foam (you may need to straighten the clip for this).
Now as you pull the hook it should close the switch.

Part 6: Finishing up.

At this point the circuit is made. Make sure you attach the resistor to the top piece of foam using electrical tape. You can now attach the battery to the power leads and test your switch. The LEDs should light up green.

Carefully insert the bottom piece of foam followed by the vertical piece, and finally the top piece of foam into the sugar dispenser. The circuit is malleable so you should be able to conform it to the shape of the dispenser. You will want to peel back the pieces and super glue them to the inside of the dispenser.

Now tighten the lid and enjoy your lantern! I swear using it in person is much more impressive than the picture managed to show.

-felix!