Chocolate Egg Detector

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

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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.
1

Connect the Crumble to power

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

!

Safety first

Make sure the battery pack switch is set to OFF.
2

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.
3

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.
4

Connect the Crumble to a computer

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

5

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.

How it works

Reed switches are controlled (opened and closed) using magnets.

When a magnet is placed nearby, the switch closes and allows electricity to flow to connector A (A is HI).

When the Crumble detects that connector A is HI, it will instruct electricity to flow to connector B (set B to HI).

The buzzer will sound until the switch is opened.

6

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.
!

Top tip

Make sure none of the metal parts of the croc leads are touching each other.

7

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.
8

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.
9

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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