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Build yours at home

Play-dough circuits

What we're doing

The dough is the wire. Salty dough lets electricity through, like the wires in Light the bulb. You squish it into a loop to light an LED, then break the loop and make a shortcut.

About 20 minutes.

Goes with these lessons

Get these parts

  • 4×AA battery holder with a switch and two wire ends (electronics shop or online)
  • 4 AA batteries (household)
  • 2 or 3 LEDs (big 10 mm ones are easiest) (Elegoo kit)
  • Play-Doh, or the salty dough below (household)

Keep it safe

Battery power only, never household power. Use AA packs matched to the parts, not a 9V battery. A grown-up connects and disconnects the pack. Stop immediately if any part warms. Never join the pack's two metal ends: the wires can get hot. Coin cells stay with grown-ups, locked away. CPSC warns a swallowed button or coin cell can burn through a child's throat in about two hours; suspected swallowing needs emergency medical care immediately.

Never push both battery wires into the same ball. Never put an LED's legs straight onto the battery wires; always go through the dough, or the LED burns out. Dough is not food, even homemade.

Steps

  1. 1
    Light the bulb

    Make two balls of dough. Keep them apart. Push the red wire into one ball and the black wire into the other. Push the LED's long leg into the red-wire ball and its short leg into the black-wire ball. Switch on. It lights! The loop goes battery, dough, LED, dough, battery. No light? Turn the LED round.

  2. 2
    Break it, fix it

    Pull one LED leg out of the dough. The light goes off: the loop has a gap. Push it back in.

  3. 3
    What if electricity takes a shortcut?

    Squish the two balls together. The light goes out, even though everything is still plugged in. Electricity takes the easy dough path instead of the hard path through the light. Pull the balls apart and the light comes back.

  4. 4

    Switch off when you're done.

  5. 5

    Switch off, disconnect the battery and put the parts away.

Talk while you build

  • Can you trace the light's whole loop with your finger?
  • What happens when we make a gap in the dough?

Spot it at home

  • Open a flashlight and find its loop: battery, spring, switch, bulb. Look at a battery toy: why does it have two metal contacts?

Where does the loop go in this flashlight?

  • Batteries come in plastic packs and boxes with covers. Keys or coins in a pocket with a loose battery can join its ends and make it hot.

Why do batteries come in plastic packs?

  • Light switches, the button on a flashlight, the toaster lever, and the button inside the fridge door that turns its light off when the door closes.

When you flip this switch, where's the gap?

Make your own dough (optional)

Store-bought Play-Doh works. To make your own:

Salty dough

1 cup water, 1½ cups flour, ¼ cup salt, 3 tablespoons cream of tartar, 1 tablespoon vegetable oil

A grown-up mixes the salty-dough ingredients, reserving some flour for kneading, and stirs over medium heat until a ball forms. Cool fully, then knead with the remaining flour. Wash hands; this dough is for building, not eating.

Grown-up references

Squishy circuits · DiscoverE Source for the homemade dough recipes.

Squishy circuits project · Science Buddies Battery and LED short-circuit warnings.

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