Electric Play Dough Project 2: Rig Your Creations With Lots of Lights!

Introduction

In Project 1 of our "Electric Play Dough" science project series, "Make Your Play Dough Light Up, Buzz, & Move!", you learned about the basic ideas of closed,open, and short circuits. If you need to review this information, you can always go back to the Make Your Play Dough Light Up, Buzz, & Move! Introduction section.

In Project 1, you only learned how to hook up one light to your creation. Imagine how cool your creations can be if you hook up lots of lights! This science project will show you how!

In order to do this, first you will need to learn about two new kinds of circuits. The examples will explain a circuit that has one battery and three light bulbs. There are different ways to connect multiple light bulbs to a battery: in "series" or in "parallel." We will explain what these words mean next.

In a series circuit, the lightbulbs are all connected in a row, and form a single loop. The path the electricity takes from the positive end of the battery to the negative end has to go through each lightbulb. This is shown in Figure 1.

Figure 1. Three lightbulbs connected to a battery in series. Notice how there is only a single "loop," and the path that the electricity takes (represented by the yellow arrows) has to go through each lightbulb in order.

In a parallel circuit, the lightbulbs are connected next to each other, and form multiple loops. Any path electricity takes to get from the positive end of the battery to the negative end only goes through one light bulb. This is shown in Figure 2.

Figure 2. Three lightbulbs connected to a battery in parallel. Notice how there are multiple "loops," and any path the electricity takes (represented by the yellow arrows) only goes through one light bulb.

One important thing to know is that the shape the wires connecting the lightbulbs makes does not matter. In other words, you can move the light bulbs and wires around, but as long as the connections stay the same, you will not change if a circuit is series or parallel. Look at Figures 3 and 4; the light bulbs have been moved around (and the shapes the wires make have changed), but they are still the same kind of circuit as Figures 1 and 2.

Figure 3. The lightbulbs in this figure have been rearranged relative to those in Figure 1. However, there is still only one path for the electricity to take, which goes through all three lightbulbs, so this is still a series circuit!

Figure 4. The lightbulbs in this figure have been rearranged relative to those in Figure 2. However, there are still multiple paths for the electricity to take, and each path only goes through one light bulb, so this is still a parallel circuit!

So, now that you know the difference between series and parallel circuits, it is time to apply this knowledge to your squishy circuits! First let us see what happens when we try hooking up first one, then two, then three LEDs (light-emitting diodes, which are a type of tiny lightbulb found in many electronic devices) in series using squishy circuits. This is shown in Figure 5.

Figure 5. (From left) One, two, and then three LEDs connected to the battery pack in series using squishy circuits. The LEDs get much dimmer as each new LED is connected.

Uh-oh! Do you see a problem in Figure 5? The LEDs get dimmer each time a new LED is plugged in. With only three LEDs, you can barely see them light up at all! This is certainly going to be a problem if you want to hook up lots of lights to your creation. So, let us find out what happens if we connect the three LEDs in parallel instead. This is shown in Figure 6.

Figure 6. (From left) One, two, and then three LEDs connected to the battery pack in parallel using squishy circuits. Each new LED is just as bright as the previous one.

That is much better! In Figure 6, all the LEDs are the same brightness. This means that when you hook lots of lights up to whatever you build, you need to connect them in parallel. Now, why does this happen? Because in a series circuit, some electricity is "lost" each time it goes through an LED. So, by the time the electricity has already gone through one or two LEDs, there is not enough energy left to power the rest of them. In a parallel circuit, the electricity goes straight from the battery to each LED without losing energy first. This allows you to light up more LEDs (you'll find a more detailed explanation in the Technical Note section below, but only if you are curious; you do not need to understand that information to do this science project).

One more important thing to note: even in parallel, your LEDs will start to get dimmer if you make a very big structure or have very long sections of conductive play dough, and use lots of LEDs. This is because some electricity is lost as it flows through the conductive dough, and there is a limited amount of electricity that the batteries can supply. You can see this in Figure 7; the LEDs that are closer to the battery wires are brighter than the ones that are far away.

Figure 7. All ten of these LEDs are connected in parallel. The electricity does not have to travel as far to get to the LEDs that are closer to the battery pack, so those LEDs are brighter. The LEDs on the far right are dimmer because the electricity has to travel much farther to get to them.

Now that you are an expert on series and parallel circuits, you are ready to start making designs with lots of lights!

Technical Note
You may be wondering why the LEDs stay bright when you connect three of them in parallel, but barely light at all when you connect three in series. After all, you are connecting the same three lights to the same battery pack; shouldn't they be the same brightness either way?
It turns out this is because of how voltage works in series and parallel circuits. The battery pack uses four AA batteries, and supplies 6 volts (abbreviated as V). Each LED requires a "voltage drop" of about 2.5 V to fully light up. So, if you connect three LEDs in series, that is 3 x 2.5 = 7.5, which is more voltage than the battery pack can supply! This is why the LEDs are so dim. However, if you connect three LEDs in parallel, they are each connected directly to the positive and negative terminals of the battery, with the full 6 V available to power each one of them. So, you can attach many more LEDs in parallel and they will remain at full brightness.

Terms and Concepts

• Closed circuit
• Open circuit
• Short circuit
• Series circuit
• Parallel circuit
• Voltage

Questions

• What is the difference between a series and a parallel circuit?
• Can you draw your own series and parallel circuits, each with four light bulbs?
• Which type of circuit is better for hooking up multiple LEDs in your squishy circuit: series or parallel?

Bibliography

The developers of Squishy Circuits have a helpful reference on series and parallel circuits:

• University of St. Thomas Squishy Circuits Program. (n.d.). Series vs. Parallel Circuits. Retrieved February 8, 2013, from http://courseweb.stthomas.edu/apthomas/SquishyCircuits/PDFs/Circuits.pdf

Materials and Equipment 

Note: if you have already purchased a Squishy Circuits Kit and the materials to make conductive and insulating play dough for a previous squishy circuits science project, you can reuse those materials and do not need to buy new supplies..

• Squishy Circuits kit (1). Includes:
  • DC hobby motor
  • Piezoelectric buzzer
  • Mechanical buzzer
  • 4 AA Battery pack
  • Jumbo LEDs (25 total — 5 each in red, green, white, yellow, and blue)
  • Conductive play dough recipe
  • Insulating play dough recipe

You will also need to gather these items:

• AA batteries (4)
• Mixing bowl
• Measuring cups
• Measuring spoons
• Spoon or spatula
• Pot you can use on the stove
• Adult helper
• Ingredients to make conductive and insulating play dough
  • Tap water (1 C.)
  • Deionized or distilled water (1/2 C.); deionized or distilled water is available in the bottled water section of most grocery stores
  • Vegetable oil (4 tbsp.)
  • Cream of tartar (3 tbsp.; note that a 1.5 oz jar is the same as 3 tbsp.) or lemon juice (9 tbsp.)
  • Flour (3 C.)
  • Salt (1/4 C.)
  • Sugar (1/2 C.)
  • Optional, but highly recommended: Food coloring
• Plastic bags or containers in which to store play dough so it does not dry out

Experimental Procedure

Making the Electric Play Dough

Follow the directions in your Squishy Circuits Kit to make conductive and insulating play dough. The directions are written on the inside of the lid of your Squishy Circuits Kit, and we have reproduced them here for convenience. You can also watch videos, below, of how the conductive and insulating play doughs are made.Important: Ask an adult to help you use the stove to make the play doughs.

Conductive Play Dough

Step	Ingredients	Procedure
1	1 cup (C.) water 1 C. flour ¼ C. salt 3 tablespoons (tbsp.) cream of tartar or 9 tbsp. lemon juice 1 tbsp. vegetable oil Optional: food coloring (a few drops)	Mix all the ingredients in a clean mixing bowl. Note that you are only including 1 C. of flour for now.
2	None in this step.	Transfer the mixture to a pot. Stir the mixture from step 1 continuously over medium heat until a dough ball forms.
3	½ C. flour	Turn off the stove. Carefully remove the pot from the heat and dump the play dough back into your mixing bowl. Wait several minutes for the mixture to cool. Once it has cooled down, knead (mix the dough with your hands) in additional flour until desired consistency is formed.

Table 1. Directions for making conductive play dough.

This video is a step-by-step tutorial on making the conductive play dough. It should help answer any questions you have about how to judge the consistency of your play dough at each step.

Insulating Play Dough

Important: We found that adding the full ½ C. of distilled water to the insulating dough in step 2 was too much (the dough became too sticky). Be sure to add small amounts of water slowly as you stir, and stop when the dough has reached a good consistency.

Step	Ingredients	Procedure
1	1 C. flour ½ C. sugar 3 tbsp. vegetable oil	Mix all the ingredients in a clean mixing bowl (especially if you used food coloring to make your conductive play dough). Note that you are only including 1 C. of flour for now.
2	½ C. deionized or distilled water	Slowly add small amounts of water as you continuously knead the dough. Do not add the whole 1/2 C. of water at once or your play dough may become too sticky. You might not need to use the whole ½ C.
3	½ C. flour	After a dough ball has formed, knead in additional flour to remove stickiness.

Table 2. Directions for making insulating play dough.

This video is a step-by-step tutorial on making the insulating play dough. It should help answer any questions you have about how to judge the consistency of your play dough at each step.

Building Electric Play Dough Circuits

1. Insert the four AA batteries into the battery pack that came with your Squishy Circuits Kit.
2. First, do an experiment to see how many LEDs you can connect in series.
   1. Start by connecting one LED to the battery pack using conductive play dough. Remember from Project 1 in our "Electric Play Dough" science project series that you should use insulating play dough between the conductive play dough pieces to prevent short circuits between the LED leads.
   2. Now, add a second LED in series, like in Figure 5 from the Introduction. Do the LEDs get dimmer?
   3. Add a third LED in series. Do they get even dimmer?
   4. Continue this process until the LEDs do not visibly light up at all.
3. Now, do an experiment to see how many LEDs you can connect in parallel.
   1. Start by connecting one LED to the battery pack using conductive play dough. Remember from Project 1 that you should use insulating play dough between the conductive play dough pieces to prevent short circuits between the LED leads.
   2. Now, add a second LED in parallel, like in Figure 6 from the Introduction. Do the LEDs get dimmer?
   3. Add a third LED in parallel. Do they get dimmer?
   4. Continue to add LEDs in parallel. Do they eventually get dimmer? Can you make them brighter by keeping them very close together?
4. What happens if you add a buzzer or a motor with the lights? Can you power more than one buzzer? How many lights can you put in series and still get sound out of the buzzer? How about the in parallel? Make a table with your results. Based on your findings which takes the most power, an LED, one of the buzzers, or the motor?
5. Now, plan out the shape that you want to make (drawing it is a good idea) and how you want to add lights. Remember that if you want to use a lot of LEDs, you will need to connect them in parallel, and that the actual shape of the play dough does not matter, as long as each LED has its own "loop" formed with the battery. You might need to use insulating play dough in some places to prevent a short circuit. Figure 8, below, shows two design examples.
6. Build your shape and start adding lights! Remember from Project 1 that LEDs only work in one direction (the longer lead should be connected to the positive side of the battery pack, with the red wire), so if one does not light up, try flipping it around. If your circuit is not lighting up at all, make sure you remembered to turn your battery pack on, and that you do not have a short circuit somewhere. If you are still having trouble, you can refer to our FAQ section.

Figure 8. Two design examples: (left) a ring of LEDs, and (right) a smiley face. Notice how both circuits use an "inner ring" and an "outer ring" to connect the LEDs to the battery pack wires, as well as some insulating play dough to let one of the wires access the inner ring without touching the outer ring (which would create a short circuit).