Activity #3: A Bright Idea. Light up an LED by wiring a circuit with a breadboard.

Take what you’ve learned in the previous two activities to build an electric car out of a cardboard box using a breadboard to build an electrical circuit using batteries, wires, two motors, and additional components.

Why do this activity?

  • Learn how to split electricity using the breadboard and wires to power more than one component. 

  • Practice adding more and more components to build and understand complex electrical circuits.

  • Build an electrical car that can be used as a base for developing a robot in future activities.

STEP #1

  Gather your supplies. For this activity, you will need:​

  • 4 AA Batteries

  • 1 4 AA Battery Holder

  • 2 DC motors

  • 2 LEDs (Light Emitting Diode)

  • 1 Button 

  • 5 Wires with Male to Male connectors on both ends (2 Black, 2 Red and 1 of Color of Choice).

  • 1 Resistor

  • 1 Breadboard

  • 2 Wheels

  • Scissors

  • Hole punch

  • 1 Cereal Box

  • 2 2-sided stickers

In Steps 2 through 7 you will put together the car by attaching the motors, wheels, and battery to the cardboard “chassis”, or car frame. 

Building the Car

STEP #2

Prepare the cardboard box to be used as the chassis, or frame, for your electric car. 

  • If you have not already done so, open both ends of the cardboard box and flatten the box as it is shown in the supplies picture. 

  • With the box flattened, cut off the top and bottom flaps of cardboard. 

Wait. How, exactly, will this box turn into a car? 

If you are having a hard time imagining your final car, think of the box as the body of your car. The wide front of your box will be the top of your car, and the back of the box will be the underside of the car. The narrow sides of the box will be the sides of the car, where the doors would be. This car will only have two wheels at the front and no wheels in the back. This means that you will need to punch holes for the axles on each side of the box, toward the front of the car.

STEP #3

  • Mark a circle on each side of the box where the axle will poke through. This circle should be:  

    1. On the narrow side of the box

    2. About 1 inch from the front of the car

    3. High enough from the bottom of the car that the gearbox of the DC motor can rest on the bottom of the box and the axle can poke through. 

  • See the picture for one example of how to figure out the right place to mark for the hole.

  • Remember to do this on both sides of the car.

STEP #4

Use the hole punch to make a hole in the spots you marked on each side of the box.

STEP #6

Attach a wheel to each side of the car by inserting the axle into the center hole of the wheel. 

STEP #5

Attach the motors to the cardboard box chassis.

 

  • Place the DC motors inside the box with the wires forward and poke the axles through the hole that you punched in Step 4. 

  • Use double-sided stickers to hold the gearbox against the cardboard.

STEP #7

Prepare the power source. 

  • Place 4 AA batteries into the battery holder 

  • Attach the battery holder to the inside of the cardboard box near the back of the car using a double-sided sticker.

  • All of the wires from the power source and the DC motors should be sticking out of the back of the car. 

Why do I have to use a 4 AA batteries this time? 

More voltage = more power. In the last two activities, the components did not require as much power. In order to power two DC motors and two LEDs, you’ll need more power. You can review the “Batteries” component card for more details about how voltage provides more power.

Building the Circuit

For Steps 8 through 14, you will build a circuit on the breadboard so that when a button is pressed, both motors turn and two LED “headlights” light up.

  • Use a wire to connect one of the positive (+) power rails of the breadboard to one of the rows that connects with the button. (Later, you will plug the battery wires into the power rails on this side of the breadboard.) 

STEP #8

Prepare the breadboard for building the circuit:

  • Plug the button into the breadboard so that it will connect the two halves of the breadboard when it is pressed down.

Repeat for the second motor.

STEP #9

Connect the motors to the breadboard so that the wheels will turn forward when connected to the power source. 

  • Plug one DC motor wire into a socket in the negative (-) power rail and the other wire into a row that connects with the button. It should be a different row than the orange wire, but on the same half of the breadboard.

How can you be sure that both wheels will turn in the same direction to move the car forward? Here are some things to consider:

  • Do the motors need to turn in the same direction for your car to move forward? 

    • How do the two DC motors fit into the box? Will one need to turn differently than the other for the wheels to spin in the same direction? 

    • Will the right wheel need to move clockwise or counter-clockwise (the same direction as the hands of a clock or opposite)? What about the left wheel? Does this matter?

  • How will current flow through the two motors? Remember that the direction of the current will affect the direction the motor spins. Will the direction of the current for each motor make the two wheels turn in the same direction? 

  • How could you test your wheels? How could you make changes to the circuit to get the results you want? This may not be clear until you connect the batteries in a later step. Keep these ideas in mind as you troubleshoot later.

Think about it.

Add an LED “headlight” to the circuit and connect it to the power rail. 

 

  • Plug the long leg of the LED into the same row as the resistor.

  • Plug the short leg of the LED into another row of sockets or the power rail on the same side of the breadboard (It will not be long enough to reach the power rail where the motors are connected, so use the closer power rail or another row of sockets).

  • Use an extra wire to connect the negative power rail or row with the LED to the negative power rail with the motors.

STEP #11

Use the resistor to begin building the section of the circuit for the “headlights” on the second half of the breadboard.

 

  • Plug one end of a resistor into one of the rows connected to the button. 

  • Plug the other end into a row near the end of the board where you will plug in your LED “headlights”. 

STEP #10

Wait. What’s the deal with the short leg and long leg? 

If you don’t remember why the LED has a short leg and a long leg, review the “LED” component card. 

Add a second LED headlight to the circuit and connect it to the power rail. In other words, repeat Step 11 using a second LED and different rows on the breadboard. 

 

  • The long leg should plug into the same row as the resistor. 

  • The short leg should plug into a row that is not connected to any other components. 

  • Use a third wire to connect the row with the LED short leg to the negative power rail. 

STEP #12

Connect the breadboard to the power.

 

  • Plug the red battery wire into a socket on the positive (+) power rail.

  • Plug the black battery wire into a socket on the negative (-) power rail.

STEP #13

STEP #14

Test your circuit:

Press the button down.

  • Do the wheels turn? Are they both turning forward?

  • Do the LEDs light up? 

Troubleshoot your circuit.

  • If one or both of the LEDs do not light up, try reversing the flow of current through the component by taking it out and switching with leg goes into the different sockets.

  • If one or both of the wheels is turning backwards, switch the red and black wires from the DC motor that you want to change. 

  • If BOTH LEDs do not light up and BOTH wheels turn backwards, try switching the battery wires on the power rail. 

  • If flip-flopping the wiring does not help, follow the flow of current through the circuit. Are there any gaps between components? 

  • Are both ends of a component in the same row of clips? 

Why should it matter if both ends of a component are connected to the same row on the breadboard? 

Sockets in the same row are all connected to the same metal clip. If you need a quick review of the breadboard connections, be sure to take a look at the “Breadboard” component card. 

If you understand how the inner “wiring” of the breadboard is organized, and you still wonder why a single component can’t be plugged into the same row, you may be thinking that the electric current is traveling from one end of the metal clip through the component, and then to the other end of the metal clip. However, electric current is much like flowing water. If there are two paths, and one is easier, it will take the path of least resistance. 


For the purpose of this activity we can assume that the resistance along the wires and metal clips is nearly zero. In fact, there is a small amount of resistance, but it is minimal. Any of the other components (not just the resistor) provide resistance to the flow of electric current. The current will take the easier path and will go through the metal clip and skip the high-resistence component all-together.

Stick the breadboard to the top of your car using double-sided stickers. 

STEP #15

Include all of the components and all of the paths that the current will travel to go through each of them.

Questions to ask yourself:

  • Are the components in a row? Does the current travel through one component and then another? 

  • Does the current split before going into different components? Can you see where the current comes back together before going back into the battery?

  • If you are still having trouble with your car, does the diagram help you to see where the trouble might be?

  • What happens if you take one of the components out of the circuit?

Sketch a diagram of your circuit.

STEP #16

Complicated Circuitry