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Lesson Overview:

Now we'll add a traffic light!

## Step 1: Introduction

A very important part of any city is a system for controlling traffic with lights. You Circuit Scribe kit comes with a perfect component for doing this: the RGB LED.

The red-green-blue (RGB) LED has 3 colored LEDs packaged on the same module. All three colored LEDs share a negative (ground) electrode, and have separate positive electrodes.

The traffic light uses the green and red LEDs, but also needs a yellow light! We get this by mixing two colors together.

1. Make sure you select the appropriate paper size using the "select paper" dropdown menu.
2. Print the circuit template by first clicking "Download PDF" and opening the file.
3. Continue on to the video tutorial!

## Step 2: Mixing Colors 1

You can practice using the RGB LED by controlling each colored LED with an individual switch.

All of the necessary components are provided in the top circuit in the Workplane. You just need to finish drawing traces using the Conductive Pen!

Can you figure out how to hook up the RGB LED using the conductive pen so each switch operates one of the colors?

1. Move onto the next step for detailed instructions.

## Step 3: Mixing Colors 2

After trying it yourself, use the instructions below to wire up a circuit that controls the red, green, and blue LEDs individually.

Notice that the ground terminal of the RGB LED is already connected to the negative (-) terminal of the battery.

1. Select the conductive ink pen and draw a connection between the positive (+) terminal of the battery to the left-hand terminals of all three switches.
2. Connect the right terminal of top switch to the "Blue" terminal of the RGB LED.
3. Connect the right terminal of the middle switch to the "Green" terminal.
4. Finally, connect the right terminal of the bottom switch to the "Red" terminal.
5. Press the "next" button below to continue.

## Step 4: Simulating the Circuit

Simulate your circuit and watch RGB LED come to life! Use the three switches to mix red, green, and blue light together.

Can you predict which colors will appear when you operate multiple switches?

Which combination of LEDs produces yellow light? (see hint)

1. Simulate the circuit and try activating each switch individually.
2. Next, try operating different pairs of switches or all three at the same time.
3. Press the "next" button below to continue.
4. Stuck? HINT: The red and green lights combine to create yellow.

## Step 5: Creating the Stoplight Circuit

Now that you have tried the RGB circuit with three switches, take a look at the second circuit at the bottom of the page. You will use this one in the City of Lights model.

The traffic signal uses red, yellow and green light, so we connected the red and green LEDs to a "slide switch."

Unlike one of the switches from your kit, which just turns an output on or off, this slide switch has three states:

Right: turn on the red light

Middle: turn on red and green at the same time to create yellow

Left: turn on the green light

1. Continue to the next step.

## Step 6: Printing Out Your Template

Now you are ready to print out the circuit template!

In the next video tutorial you will learn how to use this template to create a traffic light model.

1. Make sure you select the appropriate paper size using the "select paper" dropdown menu.
2. Print the circuit template by first clicking "Download PDF" and opening the file.
3. Continue on to the video tutorial!

In the next lesson you will learn more about the traffic light!

Next Lesson:Traffic Light Video

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