@scichelli #thatCircuits

Facilitated by

Sharon CichelliPrincipal Technical LeadHeadspring in Austin, Texas

With thanks to

Squishy Circuits University of St. Thomas http://www.stthomas.edu/squishycircuits/

CircuitsIn Play Dough

Try this!

If the blobs touch, the LED won’t work.

Building a Circuit• A circuit is an unbroken loop

for electricity to flow through.• Use the dough to connect each LED leg to a

battery terminal. • But don’t let the two clumps of dough touch each

other. That’s a short circuit.• Not lighting? Flip the orientation of the LED.• Nothing special about the dough; salt water

conducts electricity. (See recipe next.)

Mix:

¼ cup water

½ tablespoon vegetable oil

food coloring

Stir that into:

1 cup flour

½ cup salt

Mix it, then knead it with extra flour until it is the consistency of fun.

Conductive Play Dough

Motors!

And buzzers!That’s tin foil,

not dough.

Motors and Buzzers• 9 volts is too much for these motors. They shut

down to protect themselves.• Each AAA battery is 1.5 volts, so two together

gives 3 volts—just right.• Use foil instead of dough. The dough has a high

resistance, so it starves the motor of enough current. The foil is more conductive.

• The buzzer motor is like the one in your phone.

Watch out for short circuits

Battery terminals connected directly to each other get hot!

An LED connected directly to the battery ruins the LED.

Short Circuits• A short circuit happens

when current flows through a different path than the one you wanted.

• In the LED + dough circuit, if the dough blobs touch, current will go there instead of through your LED. So the LED doesn’t light.

• Foil has much less resistance than dough; foil lets more current through. LED + foil, the LED gets more current than it can handle. Permanently.

Did you fritz an LED during the workshop? Don’t sweat it; they cost pennies.

Now we’re learning about current!

Keep making circuits!• The recipe is a few slides earlier.• Batteries, battery holders, LEDs, motors,

speakers, sensors… can be found on Amazon, eBay, Adafruit.com, Sparkfun.com, and at Fry’s and Radio Shack. (Shush. I miss the Shack.)

• These LEDs are through-hole (not itty bitty surface mount), 10mm diameter (5mm is fine), and have a forward voltage (minimum volts to work) of about 2.7 volts.

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