This wreath is made out of 101 LEDs and two pieces of wire, with no other components. It can run on a 9-volt battery.

A chance encounter with a 100-pack of green LEDs inspired my daughter and me to make an wreath totally out of LEDs. We wound up using 96 of the green ones, plus 5 red LEDs left over from a previous flea market visit, for a total of 101 LEDs.

It can be twisted together without tools, but soldering makes it sturdier and a pair of needle-nosed pliers and a third hand jig will make it easier.

ROHS LEDs (about a dollar more per pack) and lead-free solder is always an option, or just wash your hands and don't stick your fingers in your mouth.

Step 1: Parts and Tools Required

The parts
100 Green LEDs
5 Red LEDs
A few feet of solid tinned hook-up wire, small gauge such as #26.
Use tinned wire, as plain copper wire would be a distracting color. You may also find special-purpose "bus wire" but don't use a gauge that's too big as it will be hard to sew.

Also Starring
You'll need a power supply or batteries capable of delivering about 0.6-1 amp at 8-10 volts, but that design is not included in this Instructable. Instead, you might like this Super-Simple LED Driver Instructable. Or just use a 9V battery.

For testing the LEDs during construction, If you don't have a power supply, you'll also need one slightly-depleted 9V battery or one fresh 9V battery and a 330 Ohm resistor.

The Tools
To finish the job, you'll need the following tools:
Solder and iron if you wish to solder (recommended but not necessary)
Needle-nosed pliers with wire cutter
Third hand jig (or make your own
Alligator-clip test leads

Step 2: Flatten the LEDs

LEDs are polarized devices, and have a plus (positive) lead and a minus (negative) lead.
The leads are distinguished in two ways:
1. The LED plastic is flat on the minus side
2. The minus is lead is shorter

Flatten the leads on 96 of the green leds, so they stick out at a 90 degree angle from the body of the LED and at 180 degrees from each other. Bend them methodically with the plus lead one way and the minus the other, so they all look the same.

Why? Because once you've bent the legs, it's hard to tell which is which without looking at the flat mark, and in the next step, it will matter which way you hook them up.

Step 3: Twist and Shout

You're going to connect the groups of LEDs in fours.

Get started by connecting two of them. If you've bent the leads all the same way, you can just pick up two LEDs, look at the bottom and orient them the same way, and twist a pair of leads together.

When you're satisfied you've got two connected with the plus of one hooked to the minus of the next, add more LEDs one at a time until you get four in a row. (That's two more LEDs, folks.)

If you're stuck, don't hook just one LED up to the 9V battery as it will not last very long at all. Instead, peer into the LED from the side and look at its internal structure. Just orient each of the LEDs the same way when you assemble them.

Construction tip: You might want to use small needle-nose pliers to twist the leads together without breaking them off or poking holes in your fingers.

Step 4: Test Your First Strand

You should now have a nice strand of four LEDs. Hook that up to your power supply set to about 8V, or a slightly used 9V battery. Better yet, if you have a current-limited supply, set it to about 20mA-30mA. If you must use a new 9V battery, series a current limiting resistor in the 330 Ohm - 470 Ohm range.

You should be rewarded with four LEDs of similar brightness. If you aren't, try checking each group of three (better use that resistor) and see if you can figure out which LED you have in backwards. If you're lucky, it won't be one of the middle ones.

You don't have to the strand for polarity, as you can figure it out easily later; but do test them all to make sure they work! If you do this now, you'll be saved trouble later, when it's harder to fix.

Step 5: Science!

This Instructable wouldn't be instructive without science, so here's a schematic diagram I made in the free version of Eagle CAD. The triangle-and-line symbol is the generic DIODE symbol, and the lightning bolt means that LIGHT is EMITTED. Now you know what LEDs are!

There is a general direction to the LED symbol as well; the flat side is closer to the ground, or minus, side, and the triangle base is closer to the plus side. Take note of these directions, as there's another twist coming up.

The V+ symbol shows where the voltage comes in, and the GND shows where the negative end of the battery is, which is by definition zero volts. So, with a 9 Volt battery, LED1 gets 9 Volts on its plus end. (That's called the anode; now don't you feel scientific!) Remember that the voltage at the bottom of of LED4 (that's the "cathode") is zero? Well, if all the LEDs are about the same, then we can assume that the "voltage drop" across each LED is about the same, or about 9/4=2.5 volts. That's a little high for green LEDs, which is why we suggested a slightly depleted 9V battery or a resistor. So let's try it again with 8.4V, giving us 2.1V drop across each LED. That should keep the green LEDs happy.

So, here's an exercise: If v+ is 8.4V and GND is 0V, what's the voltage in the middle?

You give up already? It's just 4.2V.

If you have a voltmeter and want to do more science yourself, try it and see!

Step 6: Doin' It and Doin' It and Doin' It Well...

OK, enough science.

Once you've got this process down, do it again and again until you've made 96/4=24 strands of 4 LEDs each. (If you bought 100, this uses up 96 LEDs and gives you four spares.)

After each strand is tested, make sure the leads are mechanically sound using the needle-nosed pliers, but take special care not to break the leads off the LEDs. If you're into soldering, at this point you might want to simply fasten the strand to a third hand alligator clip tool and solder away, but do twist the leads together at least enough to make a mechanical connection, as solder is not good for that job.

Step 7: Crossed Wires

We're going to get our wires crossed, on purpose.

Remember how the wreath looked woven? That effect comes from crossing two strands of the four-led sections you made earlier.

And remember how the voltage started high at the top and went to zero at the bottom? And at at the middle, the voltage was, well, in the middle?

We're going to make the X's by hooking the middle spots of each strand of four LEDs together, and since the middle at the same voltage, it's not going to cause any sparks. And here's the twist you were promised earlier! In each X, hook one set of LEDs up backwards.

How can we do this? Didn't I say we have to get the anode and cathodes all the same way to make LEDs work?

Yes, but hold on: If you start at 8.4V and go down to zero, the voltage in the middle is 4.2V, and if you start at 0 and go up to 8.4V, the in the middle, the voltage is still 4.2V. So we're still going to hook plus to the plus side and minus to the minus side, but we're doing it in a fancy way.

Read on...

Step 8: Testing One...two..three..four

Let's test this out. Use your low 9V battery (or good one and resistor) and keep trying pairs of wires in a V (not straight across) until you find a pair that lights up half the LEDs in a V, just like in the picture.

No matter how you crossed the wires, you'll always find a pair of wires that works. (If you want to use science, you can prove this to yourself. If not, push on.)

If you brought your voltmeter, measure the voltage from plus to minus, then from minus to the middle and see if it's about half. Because of minor variations in the LEDs, it won't necessarily exactly be 1/2, but it will be close enough.

OK, it works, but why are we doing this? When we arrange all these X's in a circle, we can put all minus leads on the outer part of the circle and all the plus leads on the inner part of the circle, and won't that be convenient!

Plus, the middle attachment points of the LEDs will make lots of triangles, giving our wreath structural stability.

Step 9: Twelve Little X's

Now go crazy and use up the rest of the green LEDs.

At the end of this step, you'll have twelve sets of LED X's.

Don't worry about polarity. As long as you've individually tested each strand of four LEDs, you'll be fine. You can't get it wrong.

Step 10: Eight LEDs a Glow-ing!

How do we get the other half of the LED X to light?

To answer this question, we must again appeal to SCIENCE!

Here's a schematic showing eight green LEDs, with a line between each pair of four, as we discussed earlier. Note there's a plus and a minus on each pair. All we have to do is hook up both of the plusses and minuses to complete the circuit and make all eight LEDs glow.

Do this with some alligator clip test leads "et voila"!

Step 11: Eight and Eight Is Sixteen

Like the glowworm, we'll go double or nothing.

Take two X's of LEDs and use handy-dandy clip leads to hook up all the positive sides and all the negative sides. Your trusty 8.4 volt battery will still power them all, because we're putting two LED X's in parallel, which means they run on the same voltage, but just take twice as much current. (So your battery will run down faster, but who cares? It wasn't that great to begin with...)

Now that you're steeped in LED science, you can follow the schematic on your own.

Step 12: One Ringie-dingie

Arrange your twelve LED X's in a clock circle, with the minus leads on the outside of the circle, and the plus leads on the inside.

After you use your battery to test each X, pick it up and orient the X so that the negative leads are at the top and the positive leads are at the bottom. Then use the needle-nosed pliers to bend up the tip of the (top) left negative lead on each X.

This bend will help you keep the orientation when you assemble the X's together in groups of three, plus it will be a slight help in the mechanical assembly of the X's.

Step 13: Two Ringie-dingie

Arrange three of the X's from the previous step with the bent-leg negative leads all at the top left, as in the drawing.

Since we want the resulting group of three X's to form a quarter circle, clip off about 1/3 of the length of each positive lead.

Join all the the three X's together at the negative leads and at the positive leads, giving a semi-circle of X's.

Construction tip: Use the needle-nosed pliers to make complementary bends at the tips of the leads so that they hook together; then use the third-hand jig to put tension on the junction as you solder it.

The result will be about a quarter-circle of LEDs.

Step 14: Three Ringie-dingie

Do the previous step four times in total, and you'll have four quarters of a circle.
Arrange them to get an idea of how the wreath will look.

You can stretch and bend the joined X's into diamonds to make the wreath more symmetric, but don't go overboard, as it will look much better than you think when it's finished and glowing green.

You might give each group a quick test by clipping negative to the outside and positive to the inside, at both ends of each quarter circle. All LEDs in each groups should glow. If not, backtrack and find the problem.

Step 15: One Ring to Bind Them...

When you're satisfied, start soldering the leads together to join the circle.

As always, the third hand is helpful.

Depending on how you want to finish the wreath off, you might want to leave one outer pair unjoined, to serve as an open area for the top or bottom of the wreath. We chose to do this at the bottom to leave room for a star of red LEDs, and then joined the two remaining leads with a loop of the solid hookup wire.

Step 16: You're on the Bus

Even though it's all in a circle, the wreath still won't work. We need to hook all the minuses together and then all the plusses together, creating what's called a power bus.

Take the small-gauge, tinned, solid wire and measure out enough to go around the outside of the loop, and then some. If you have to remove the insulation from the wire, do so now using wire strippers or your needle-nosed pliers (and their inner cutting surface). Do this in stages, and be careful not to cut or brush-burn your fingers with the wire edge or insulation.

First, form the negative (ground) bus. Sew one strand of wire through the outer points of the wreath, and tightly wrap the loose ends around the pair of LED leads that you left unsoldered. You might want to loop the wire once around each junction as it passes through, to give some mechanical stability. Make sure the wire is straight between junctions, but don't pull so tightly that it distorts the circular shape of the wreath.

Now, do the same for the inner loop, which will form the positive bus. Take care not to touch any other leads of the LEDs with either bus.

Step 17: Luke's Fiat

Yes, we're off the bus and into a sports car. But what I meant to say was Lux Fiat!, or as the Roman's said, Let There Be Light!

Your 9v battery might or might not do the trick at this point, so if you have a power supply, expect about 25mA * 24 = 600mA.

Note the two bus wires around the outer and inner edges of the wreath, which I cleverly described (but didn't show) in the last step. Sorry.

If this all works, take your soldering iron (if you're so inclined) and touch up the functions for the plus and minus bus wires.

Step 18: Do It in the Dark

Go ahead, turn out the lights and see what you see.
If you've done everything right, it should look like this.

Step 19: Better Red

Red LEDs generally have a lower voltage drop than green LEDs, so we'll use five instead of four.
Try twisting five of them together and running the ensemble off your low 9V battery or good battery and 330 Ohm resistor. If the LEDs seem too bright for their own good, you'll have to incorporate a higher resistor or perhaps change the design or change the LEDs, but most likely it will all work out.

Twist the five red LEDs into a pentagonal shape, or make a bow out of them, or any other shape that strikes your fancy. Here's your chance to go crazy!

Step 20: A Star Is Born

Attach the red LED ensemble to the area you cleverly left open on the wreath, and touch it up with a soldering iron.

Remember to hook the negative lead of your power supply to the outer bus, and the positive one to the inner bus. A discarded piece of Ethernet cable will provide several pair of festive twisted pairs of wires so you can select the color of your choice to make the final connection.

You should be pretty admiring of your handiwork at this point, and have no doubt attracted a crowd of curious onlookers. It's time to give them (and yourself) the treat you deserve.