Chocolate Egg Detector

Build a buzzing egg detector and add another dimension to an egg hunt for your friends or family.


things you will need

The following items from the Discover Computing kit:

  • 1 x Crumble
  • 1 x Battery pack
  • 2 x Red croc leads, 3 x Black croc leads, 1 x Green croc lead
  • 1 x USB cable
plus a Crumble-friendly reed switch and a Crumble-friendly buzzer (both items can be purchased here).

A computer with a USB port and the Crumble software installed.

To make the egg detector holder, you will need:

  • A4 card
  • Craft scissors
  • Double-sided sticky tape (or regular tape)
  • Rubber bands
Lastly, to play the game you will need some plastic eggs, chocolates and fridge (or small) magnets.

Connect the Crumble to power

Use one red croc lead and one black croc lead to connect the Crumble to the battery pack.


Add the Reed Switch

  • Attach one red croc lead to a positive (+) connector on the battery pack and to any connector on the reed switch.
  • Add one black croc lead to the remaining connector on the reed switch and the ‘A’ input/output connector on the Crumble.

Add the Buzzer

  • Attach one black croc lead to a negative (-) motor connector on the Crumble and the negative (-) connector on the buzzer.
  • Add one green croc lead to the remaining connector on the buzzer and the B input/output connector on the Crumble.

Connect the Crumble to a computer

Use the USB cable to connect your Crumble circuit to a computer with the Crumble software installed.


Code the detector

  • Snap a ‘do forever’ loop to a program start block.
  • Tell the Crumble to turn the buzzer ON if the reed switch is closed, otherwise leave the buzzer OFF
  • Turn the battery pack ON.
  • Send your code to the Crumble (using the green triangle) and test it out.
  • Grab a magnet and place the magnet on the reed switch.

Assemble the egg detector

  • Unplug the USB cable from the Crumble.
  • Place the Crumble on the back of the battery pack, with the croc leads all pointing upwards.
  • Take the buzzer and place on the front of the battery pack, with the croc leads all pointing upwards.
  • Use a rubber band to secure in place.

Make the egg detector holder

  • Turn the battery pack ON.
  • Place the assembled egg detector next to one of the shorter sides of the A4 card. 
  • Roll the card around the assembled egg detector, leaving the reed switch outside of the card.
  • Secure the sides in position with sticky tape.
  • Fold and sticky tape the bottom of the card roll (the battery pack end).
  • Fold the corners of the top end of the card roll inwards, leaving the reed switch outside of the roll and facing towards you.
  • Secure the folds in place with sticky tape.

Decorate the egg detector

  • Turn the egg detector so the back (the side without the red rectangle) of the reed switch is facing you.
  • Cut shapes out (we used an egg shape) and attach to the end of your egg detector – so the switch is hidden.
  • Get creative and decorate the rest of the egg detector holder.

Set-up the egg hunt

  • Check once more that your egg detector is working. Place a magnet against the reed switch. If the buzzer sounds, then you are good to go!
  • Tape small magnets inside some (not all) of the plastic eggs.
  • Add chocolate eggs to those eggs with a magnet inside.
  • Hide the eggs and take it in turn to find the eggs with chocolate inside using your new egg detector!

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