Institute of ImaginationRobot LabRobot Lab
Give it a brain

Light-up card with a paper circuit

Join an LED to a coin cell battery with copper tape. Fold down a card flap and the LED lights; lift it and the light goes out.

  • About 45 minutes
  • 6 steps
Step by step

One step at a time, in big writing.

A round cardboard badge with two drawn eyes and a hole for a mouth, and a green LED lit at the side

Before you start

What you need

Tools

To print

Materials

Make it

The steps

Everything goes on the front of your card: the LED, the tape and the battery.

How it works

Electricity flows from the battery, along one copper strip, through the LED and back along the other. It only flows if the path has no gaps, and only one way through the LED, so the long leg joins the + side. If the strips touch, the electricity skips the LED. The flap is a switch: down closes the gap, up opens it, and that on or off is a signal, like the ones a micro:bit sends.

The circuit card from above, twice. With the flap lifted off the battery the LED is dark; with the flap folded down onto the battery the LED lights, and arrows show the electricity going round from the battery along one copper strip, through the LED and back along the other.

  1. An LED lighting up with a coin cell battery between its legs: the long leg on the plus side, the side with the writing, and the short leg behind on the minus side

    Test the LED on the battery

    Slide the LED's legs either side of the battery: the long leg on the + side, the side with the writing. Does it light?

  2. The LED on the card with its legs bent flat out to the sides, each leg on a small square of copper tape; plus by the long leg, minus by the short leg

    Stick the LED on your card

    Draw your shape and choose a spot for the light, at least 2cm from the edges. Stick two small squares of copper tape there, about 1cm apart. Bend the LED's legs flat out to the sides, once only, and sit one leg on each square. Write + by the long leg and − by the short leg in pencil.

  3. A copper strip from each leg: the plus strip runs down and along to the edge of the card, the minus strip ends in a square for the battery, and the two never touch

    Lay the copper strips

    Lay a strip of copper tape from each leg, over its square, so the leg is sandwiched. Peel off the backing a little at a time and press the tape flat. End the − strip in a square about 2cm across, for the battery. Run the + strip to the edge of the card next to the battery square. Keep the strips apart everywhere.

  4. A flap of card taped to the edge, folded open, with the plus strip carried onto it to the spot that folds onto the battery square

    Make a card flap

    Tape the small card to the edge beside the battery square with brown paper tape. Carry the + strip onto the flap, to the spot that folds onto the square. Does the copper land on the square when you fold it?

  5. The card from above, twice: first the coin cell battery on its copper square with its plus side up and the flap folding over onto it; then the flap folded down over the battery, held with masking tape, and the LED lit

    Put in the battery and close the flap

    Put the battery on its square, + side up. Fold the flap so its copper presses on the battery. Does your LED light? Hold the flap shut with a binder clip or masking tape. Lift it to switch off.

  6. A small card robot with the same paper circuit on its front, the LED as a light on its chest

    Invent your own

    Make your own light-up thing. Where else could your robot have a light?

After the steps

Use it on your robot

Build the circuit on a small card and glue it to your robot's head for an eye.

For ideas

  • A cardboard monster badge with a big toothy mouth and a blue LED lit as its eye
  • The top of a cardboard badge, with stars drawn on it and two white LEDs lit along its top edge
  • The back of a different badge, built another way: two LEDs pushed through holes from the front, with copper tape, a coin cell battery and a card flap on the back
  • A small cardboard robot standing on folded legs, with copper tape tracks on its front, a red LED and a binder clip holding the battery
  • A robot made from a folded cardboard triangle, with copper tape along one edge, a spotty disc and a shiny clear disc for eyes

Your turn

Ideas to try

Make something else

  • Robot eyeswith two LEDs side by side.
  • A robot with a glowing heartin the middle of its chest.
  • A lighthousewith the light at the top.

Then change something

  1. Add a second LED, long leg on the + strip. Do both light?
  2. Turn the LED round. What happens?
  3. Hold tissue paper or coloured cellophane over the LED. How does the light change?
  4. Use foil on the flap instead of copper. Does foil carry electricity?

iOi challenge

Make a robot whose eyes light up only when you press its nose.

More to make

  • Build a body

    Kaleidoscope boxes

    Glue your circuit inside a cube head, and its coloured windows glow.

    • About 45 minutes
  • Build a body

    Make it roll!

    Glue your circuit to the front of a box with wheels, and it has a headlight.

    • About 40 minutes
  • Give it a brain

    micro:bit name badge

    Glue LED eyes above a micro:bit, and its lights make a changing mouth.

    • About 45 minutes