Easy to make 'Flying Saucers' based on home-made conductive play-dough 'Squishy Circuits'.

“Squishy circuits are a project from the Playful Learning Lab at the University of St. Thomas. The goal of the project is to design tools and activities which allow kids of all ages to create circuits and explore electronics using play dough.”

http://courseweb.stthomas.edu/apthomas/SquishyCircuits/

Step 1: What You Will Need

Conductive play-dough (see below)
5mm red LEDs (Light Emitting Diodes). Approximately eight per saucer
PP3 battery
PP3 battery clip
3 inch wooden disc (available from craft shops).

You can make your own conductive play-dough using the recipe published by the University of St Thomas. Regular play-dough that can be bought in the shops is also conductive but not as much as the recipe below.

Conductive Dough Recipe: Makes approximately 500g play-dough

1 cup water
11⁄2 cups of flour (hold back 1/2 cup for kneading)
1⁄4 cup of salt
3 tbsp. Cream of Tartar or 9 tbsp. lemon juice
1 tbsp. vegetable oil
food colouring

Source: http://courseweb.stthomas.edu/apthomas/SquishyCircuits/conductiveDough.htm

Start by mixing together the solid ingredients (remember to hold back 1/2 cup flour), then the oil, then add the water gradually while stirring. This seems to be the best way to avoid lumps. The Cream of Tartar is the 'active' ingredient that increases conductivity. Add colouring (optional) then knead on a board with the remaining flour as required to get the right consistency. It will stay fresh in the fridge wrapped in film for a couple of weeks.

Step 2: Roll Out Two Play-dough Balls

Roll out two play-dough balls about 1 and a half inches diameter. These are going to be connected to the positive and negative sides of the battery and will be separated by the insulating disc.

Step 3: Squish the Ball Onto the Disc

Squish the ball onto the disc, cupping it in your hand to form a dome. This will be the underside of the flying saucer.

Step 4: Seal the Battery

We'll use a 9V (PP3) battery. Clip on the battery connector. The battery is going to be buried in the play-dough so first we need to seal the terminals with some masking tape to prevent the play-dough oozing in and creating a short-circuit.

Step 5: Place the Battery on Top

Turn the saucer over and place the battery on top. The play-dough should be sticky enough to hold it in place.

Step 6: Cover the Battery

Use the second ball of play-dough to cover the battery. Gently cup the dough to create a dome-shaped top to your saucer. Make sure the two sides of the saucer aren't in direct contact.

Step 7: Add an LED

Insert the exposed ends of the battery leads into each side of the play-dough. Add an LED to test the circuit. Splay out the legs of the LED slightly and push the legs into the dough, one with side of the wooden disc. As a diode they'll only work one way around (the shortest leg is the cathode that should be connected to the negative battery terminal). The LED should light up. It's OK to experiment - it won't break the LED.

Avoid connecting the LEDs directly to the battery terminals as this may release the magic smoke. The play-dough functions as a resistor that lowers the voltage across the LED.

Step 8: Add the Rest of the LEDs

Arrange the LEDs around the circumference of the flying saucer. Remember that the LEDs are small parts with sharp legs so the flying saucer should be assembled under adult supervision. The LEDs can be turned off, or made to 'flash' simply by removing one of the battery leads.