The following information is a single lesson in a larger project. Find more great projects here.

Lesson Overview:

Now we'll learn to control LEDs and use switches!

## Step 1: Light Emitting Diode (LED)

The light emitting diode (LED) lights up when a large enough voltage is applied across it’s positive and negative electrodes.

The LED is a type of “diode”, which is like a one-way street for current flow. Current only flows in one direction, and is blocked in the other direction.

Usually LEDs only work in one direction. Circuit Scribe LED modules have 2 LED’s wired up in opposite directions, which lets you flip the LED around to alternate its color between blue and red.

1. Add a Bi-LED component to the right of the Bi-LED on the canvas.
2. Connect the terminals of the new Bi-LED to the Bi-LED that was already on the canvas.

## Step 2: Making a Circuit

You can use a 9 volt battery and the Bi-LED component to see how the it works.

1. Simulate the circuit.
2. Stop the simulator and rotate the LED 180 degrees. What happens?
3. Print and try it out.

## Step 3: Parallel Circuits

When two components are in parallel they both receive power from the battery independently.

If a component is removed from the circuit the other components will continue to function because it is still a closed circuit.

In a parallel circuit the voltage in each branch is the same. The sum of the current in the branches should be the same as the total current.

1. You will now design a parallel circuit.
2. Add a Bi-LED component to the right of the Bi-LED on the canvas.
3. Connect the terminals of the new Bi-LED to the Bi-LED that was already on the canvas.

## Step 4: Testing a Parallel Circuit

Let’s test the circuit and see what happens when we remove modules.

1. Simulate the circuit. How many LEDs are on?
2. Stop the simulation.
3. Select one LED and move it away from the traces.
4. Simulate again. Now how many lights are on?
5. Try replacing the LED and removing the other. Now what happens?
6. Print out your template and try it!

## Step 5: Designing a Series Circuit

In a series circuit the current running through each component is the same. The sum of the voltage in the components should be the same as the total supply voltage (9V from our battery).

1. Delete the elements on the canvas.
2. Place a 9 V battery , and 2 LED’s in the workplane.
3. Arrange the components so the 9 volt battery and one LED are across from each other. Place the other LED centered above the other modules.
4. Use the conductive pen to connect the positive(+) of the battery to one side of the top LED. Connect the other side of the top LED to one side of the side LED. Finally connect the other side LED to the negative (-) end of the battery .
5. Simulate the circuit.Try removing one of the LEDs and simulate again. What happens? Try it again with the other LED.
6. Print out your template and try it!

## Step 6: Single-pole Single-throw Switches (SPST)

The single-pole single-throw (SPST) switch is like a regular light switch: in one position, the circuit is closed (connected) and in the other position the circuit is open (not connected). The LED will turn on and off when you flip the switch.

1. Remove the top Bi-LED from the canvas.
2. Put an SPST Switch component on the pads of the removed Bi-LED
3. Simulate the circuit and try flipping the SPST switch.
4. Print out your template and try it!

In the next lesson you will learn to use transistors!

Next Lesson:Get Amplified with the NPN Transistor