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Blinky USB LED Christmas Trees

For the holidays, I made a pair of USB-powered blinking Christmas trees. Trees were from the dollar store, the decorations (a mini-garland and some charm bracelet charms for ornaments) were from the hobby supply store. The rest was from my parts bin. (Meaning: It doesn't use a 555 timer chip, and it doesn't use a microcontroller!)

Now these pretty little trees, when plugged into a free USB port, light up and blink a mini string of red and green LEDs. Technologically they don't push any envelopes, but they were fun to make and fun to have around. They make a great gift, too!


To make each tree, I needed:

  • 1 small xmas tree

  • small decorations for the tree

  • cyanoacrylate glue (crazy glue)

  • few feet of green or black wire

  • 4 or 5 red leds

  • 4 or 5 green leds

  • 74HC14 Schmitt Trigger Hex Inverter chip (7404 will not work!)

  • 2uF capacitor (or two 1uF caps in parallel)

  • 1 Megaohm resistor

  • USB cable from a mouse or something

This will give you a string of 8-10 LEDs that will flash 1 second on, 1 second off for as long as it's plugged into a USB port.

Basic Flasher Circuit

This is the basic flasher circuit. You might want to make just the flasher circuit on a breadboard first to make sure you have it right. The following schematic will blink the LED regularly.

Assuming you got the basic flasher circuit shown above working, then consult the schematic to the left (click for a larger version) for the changes you need in order to drive a string of 8-10 LEDs instead. The string of 8-10 LEDs will be our miniature string of Christmas lights for our miniature tree.

Build The LED String

To build the string of LEDs, I would suggest holding two parallel wires (black or green will be concealed in the tree better than other colors) in some helping hands.

Then with a wire stripper, strip away sections of the wire jacket so you can solder the LED leads onto the wire within.

You don't need to actually remove sections of jacket. You only need to cut and stretch/push it out of the way enough to solder on the LED.

Make sure to solder all LED leads in the same orientation. All long leads face one way, all short leads face the other way. Very important!

Afterwards, snip off the excess on the leads. This will leave the soldered backs of the LEDs exposed, so don't let them touch anything metal or they will short out. If you are concerned, you can apply some hot glue to the exposed metal to insulate it - but I didn't bother since the LEDs are going to be in the tree shortly, where the exposed leads will be protected.

Now that you have a nice string of LEDs, hook it up to the driver circuit you built.

Don't worry about the polarity of the whole thing, just plug it in one way, and if that doesn't work, use the other way. Plugging in the LEDs backwards into this circuit won't harm them.

USB Power Supply

Now that the string of LEDs is blinking, we need to give it power from USB. I cannibalized a cable from an old USB mouse; I just hacked it off and stripped the wire end bare.

If you're in luck (like I was), whatever USB cable you choose to cannibalize will have a RED and BLACK wire inside, which a voltmeter confirms is +5V (mine was +4.7 actually) and GND. If you're not in luck, just probe around with your meter on a wire pair at a time. There are only four wires in the USB cable. Just don't short any of them.

You could even look up the pinout for USB plugs and trace back the wires to the correct contacts, but if you want to be that precise I'm afraid you're on your own.

Once you have found the appropriate wires for GND and +5V, hook those up to your driver circuit. Plugging in the USB cable will make the LEDs start blinking.

Trimming The Tree!

Now that your circuit is working, your string of LEDs are lighting, and you have a USB plug to power it all, it's time to make that little tree!

We need to attach the lights, then decorate it.

The Lights: This is where the CA glue comes in. Start at the top of the tree with the end of your string of lights. Nestle the first LED in there, then spiral your way down the tree with the rest of the string of lights. Anchor the LEDs and wire in place with CA glue - just drop it right on the wire and LEDs where it comes in good contact with the tree. Leave it alone for a while, and the CA glue should set up nicely on just about whatever your tree might be made of. This will secure the lights. (You could try hot glue, but on such a small item I find it's too messy.)

Decorations: CA glue works here too. Just mount your little decorations, then drop some CA glue onto where it meets the tree. If you don't have anything suitable for decorations, little charms for charm bracelets or beads work well.

So, just for fun - what would you suppose a bunch of headless Lego-people would want most to find under the tree on Christmas?

Video (This doesn't really need a video, but we all love "screenshots" so here goes!)

Merry Christmas!

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