Introduction: Christmas LED Tree

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About: I'm a teacher (physics, grades 7 to 10), Maker and product designer. (Check out www.slimme-handen.nl full of experiments, projects for Maker Education and kits for Bibberbeests!). Besides that, I write childre…
7 LEDs make a christmas tree.

If you can solder a little, you can make a christmas tree without hurting any trees. It takes 7 LEDs, some wire and a battery. That's it.

The video below features some LED Christmas Stars as well. The making of the Stars is covered in a separate Instructable.

No video playing? Have a look at it here...

So get your soldering iron, grab your LEDs, find some batteries and kick off the christmas decorating season.

If you're uncertain about your soldering skills: Start with making the star (over here). It's easy. You can do it. Really. Trust me.

Step 1: Stuff and Tools

For a christmas LED tree you need:
  • 6 green LEDs, 5mm dome
  • 1 red led, 5mm dome
  • 10cm of thin copperwire, insulated.
  • Optional: 120 Ohm resistor
All parts for the star and the tree can easily be ordered at RadioShack, Mouser (if you live in he US), or Farnell or Conrad (Euro's, Aussies, rest of the world).
If you're new to electronics: buy a assortment of LEDs like this one.

Costs:
The tree costs about €2,- / US $2,60

Tools and other stuff needed:
  • For a template: 5mm plywood or something similar.
  • Soldering iron and solder
  • Pliers or pincers
  • Polymer clay or a third hand to fix parts for soldering
  • Multimeter for debugging

Step 2: The Circuit of a LED Christmas Tree...

The Led Christmas Tree's circuit consists of three separate circuits, all connected to the same battery:
  • On the left side of the tree: 3 green LEDs in a row (that is, in series).
  • On the right side of the tree: 3 green LEDs in a row.
  • On the top one red LED.
The switch in the circuit is not a physical part of the tree: The tree lights up by planting a wire into the plus-connector of the battery.

What can go wrong?
The easiest mistake to make is connecting the LEDs in the wrong "direction". Have a look at this I'ble (step 2 is about LEDs) if you're not sure about LEDs having a direction...

Step 3: Connecting the LEDs on a Template

To make soldering the LEDs as easy as possible, I made a template out of plywood. A PDF file with the template is enclosed with this step.
  • Start with the three green LEDs on the left side of the tree.
  • Place the LEDs "head-to-tail" on the template. Make sure the plus-side of the LEDs face the top of the tree.
  • Bend the LEDs' leads in an angle so that adjacent leads cross each other. 
  • Fix the leads on the template with sticky tape or polymer clay.
  • Solder the crossing leads (two times).
     
  • Do the same for the three green LEDs on the right side of the tree.
     
  • Now solder the plus-side of the red LED to the plus side of the upper green LED on the right side of the tree. See picture 4.
     
  • Connect the minus-side of the red LED to the minus-side of the upper green LED on the left side with a piece of insulated wire. See picture 6.
     
  • Connect a piece of wire (about 10 cm) to the plus-side of the upper green LEDs. See picture 7.

Test it:
Connect the ends of the star to the battery's poles. Mind the polarity of LEDs and battery! If the LEDs light up: Hooray. If not:
  • Most likely, you connected at least one of the LEDs head-to-head instead of head to tail.
  • If you lined up the LEDs correctly and it is STILL not working (this happened to me...): One of the LEDs might be broken. Check each led individually with a multimeter or a 3V coin cell or, if you have it, a 3V power supply.

Solder a sturdy, solid copper wire (about 4 cm / 1.5") to the minus-side of the LED string. See picture 3 in this step.

Attachments

Step 4: Prepare the Battery

The batteries I use have a plastic wrapping that can be removed easily with a sharp knife. Under the wrapping is a clean zinc casing, which I like a lot...

Cut a piece of sturdy copper wire a bit longer than the battery's width (about 3.5 cm / 1 1/4").

Important: You're about to solder the copper wire across the battery's poles. To avoid a shortcut, you need to isolate part of the copper wire FIRST.
  • Align the copper wire so that is centered with the top of the battery (picture 2).
  • With ducttape, cover the part of the copper wire that crosses the battery's plus-pole (the smaller connector).
  • Now place the copper wire over the top of the battery. Make the wire touch the minus-pole (the bigger connector).
    Make sure that no bare copper touches the battery's plus side! See picture 3.
  • When all is in place, fixate the wire with some plymer clay to the battery.
  • Solder the wire to the battery's minus-pole.

Step 5: Finish Up...

Almost done! What's left is connecting the tree to the battery. No biggie.
  • Lay down the battery and the tree flat on the table.
  • Lign up the tree so that the red led is above the center of the battery.
  • Solder the lowest leads to the copper wire on the battery.

TEST IT!
Now, when you connect the wire from the top of the tree to the battery's plus-pole, the tree should light up.

When all is well, trim the wire to a length you like.