Christmas Jumper Day

Today is Christmas Jumper Day! So, if you have forgotten yours, there’s still time to put 13 LEDs to good use.


You’ll need:

  • 12 mixed white, blue, yellow LEDs + 1 red LED
  • LilyPad Arduino
  • Conductive and normal thread
  • Coin cell batter + switched holder
  • 1 old t-shirt
  • 1 blue jumper
  • Felt (for the moon)
  • Permanent black marker or black paint


  • Some alligator clips for testing
  • Breadboard, wires, FTDI cable
  • Small bells

1) Preparation
Start by laying your jumper on a flat surface, lay the T-shirt on top, to see if it is going to fit inside the jumper.

Cut out a large circle in thick felt, that will be the moon. Draw the silhouette of Santa’s sleigh on the moon, making sure the reindeer at the front is on the edge of the circle (there will be a red LED coming through the jumper for its nose!).

2) LEDs and code
jumper1Start by testing out one LED with alligator clips and your LilyPad Arduino. Don’t forget to change the Board option in your Arduino IDE or the sketch won’t upload properly. Also, if you’re not using a LilyPad USB, you will need an FTDI cable to connect the board to your computer.

Next test all your LEDs, by arranging them on a breadboard. I want the yellow, white and blue LEDs to blink at different rates, and the red one to be always on.

All the LEDs of the same colour are wired together, and will therefore have the same blinking rate.

Here’s the very simple code that needs to be uploaded to the board:

const int redPin = 6;
const int yellowPin = 8;
const int whitePin = 10;
const int bluePin = 12;

void setup() {
  pinMode(redPin, OUTPUT);
  pinMode(yellowPin, OUTPUT); 
  pinMode(whitePin, OUTPUT); 
  pinMode(bluePin, OUTPUT);
 digitalWrite(redPin, HIGH);
 digitalWrite(bluePin, HIGH); 

void loop() {
  digitalWrite(yellowPin, HIGH);
  digitalWrite(yellowPin, LOW);
  digitalWrite(whitePin, HIGH); 
  digitalWrite(yellowPin, HIGH);
  digitalWrite(bluePin, LOW);
  digitalWrite(yellowPin, LOW);
  digitalWrite(yellowPin, HIGH);
  digitalWrite(yellowPin, LOW);
    digitalWrite(whitePin, LOW);
  digitalWrite(yellowPin, HIGH);
  digitalWrite(bluePin, HIGH);
  digitalWrite(yellowPin, LOW);

And the result:

Make sure you test your circuit with the coin cell battery rather than the power of the computer, because the voltage will be a lot lower, and your LEDs not as bright; so check you’re happy with their brightness.

3) The jumper
Start by pinning the moon in place on the front of the T-shirt, to make sure you’ll put the LEDs around. Prepare the LEDs (i.e. curl up their legs, ready to be sewn). Put them in place on the T-shirt, sewing them loosely with normal thread (You can even use different colours to identify the + and – sides of the LED). Also put place your LilyPad with the sketch on at the bottom of the T-shirt.

Finally, sew up all the LEDs to the LilyPad with conductive thread. Ensure you don’t create short circuits by crossing lines over.

Remove the moon from the T-shirt.
Then, turn the jumper inside out, place the T-shirt so that the LEDs will show trough the front of the jumper. Sew the front of the collar, arms and waist together with normal thread. Turn the jumper back. Put it on.
Help the LEDs find their way through the mesh of the jumper, then pin the moon in place on the front of your jumper.

Sew the moon in place, and you’re done.
Finish up by adding little bells to the jumper for an even Christmassier feel!


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