Secret Santa

Hello! Time to send your list to Father Christmas! That’s why today we’re writing secret messages and reading them with 2 UV LEDs.


You’ll need:

  • 2 5mm UV LEDs
  • A UV marker
  • 1 coin cell battery
  • Conductive tape and paint
  • Coloured papers


  • Googly eyes
  • Chenille wires

So, we are going to make an envelope that is shaped like Santa’s head; the circuit will be on the inside and will consist of 2 UV LEDs and a battery. You can then insert a message written with a UV marker inside the envelope.

1) The envelope
I am using red, gold and white glossy paper to make and decorate the envelope. The base will be red. On the other side of the red paper, print the template below, which also has our circuit for the second part of this tutorial.

On the front on the envelope, either draw a face or cut out and stick the pieces below.

You can, if you want, stick some googly eyes and white chenille wire to make the base of Santa’s hat. If you’ve got some of this left, you can roll it into a white circle and stick it at the back of the envelope as a seal, later. When the envelope gets opened, the top lid will look like a hat.


2) The LEDs
Now that the appearance of envelope is ready, we need to take care of the circuit. Just like for yesterday’s activity, I am going to be using this paper battery holder. Start by constructing the battery holder with conductive tape, sticking the excess to the back of the envelope and following the circuit from the template. Also add conductive tape on the sides, where the LEDs are going to be. Then complete the circuit with conductive paint.

Add the LEDs, fold and assemble the envelope. Once this is done, finish up by adding connections to the parts of the circuit that are missing them (mainly at the junction of the 3 panels) using a paintbrush and conductive paint. Make sure those panels are well stuck together, otherwise the circuit might not work.

3) Write your secret message
That’s it! All you have to do now is find a card that would fit into the envelope, write a message with UV marker and attach a coin cell battery. And send it! The receiver will be able to read your message once the battery is put in place.

Hopefully, you’ll be back tomorrow for fun with 3 LEDs!


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