Introduction: A Single Switch

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

Project Overview:

Have you ever wondered how that light switch at the bottom of a staircase is sometimes flipped up to turn the light on, and at other times flipped up to turn the light off, and that the same is true for the switch at the top of the staircase? This lesson will help dispel the mystery and teach you some basic circuitry concepts along the way!

Step 1: Three Simple Components

Starting with a blank "canvas", we will drag out the various components in order to demonstrate a simple light switch. This simple circuit will demonstrate some fundamentals of switching in a single switch set up before moving on to a three-way switch.

Key Concepts:


-Component Drawer

-Rotation of components

  1. Click on the "+ Components" menu.
  2. This opens the store of components in the window at the bottom of the screen.
  3. Scroll down until you find the "SlideSwitch"
  4. Click and drag out a SlideSwitch onto the work surface. (You will notice, when you drag out your switch, it may not be oriented correctly. Once you place it on the canvas, you can rotate the switch by clicking on the "rotate" tool in the upper left. You will need to make sure the object you wish to rotate is selected.)
  5. With the "Components" drawer still open at the bottom of the screen, drag out a "9V Battery" as well as a "Light Bulb"

Step 2: Terminals, Terminals and Terminals!

In this step, you will get a better understanding of what terminals are and the function they play in a circuit.

Key Concepts:

-Component terminals

-Common terminal

-Battery terminals

  1. Now that you have added your various components, hover over the little "terminal" nodes on the bottom of the light bulb.
  2. Instruction image When hovered over the terminal, notice the the light bulb labels them "Terminal 1" and "Terminal 2". When powering a light bulb, there is no "+" or "-" terminal, as either one can play the role. The important thing is a current will need to "pass through" the light bulb. One terminal will trace back the "+" (Positive) side of the bulb, while the other will trace back to the "-" (negative).
  3. Now hover over the 9v battery terminals. Notice that they are labeled "Positive" and "Negative" to indicate the direction that the current will flow. (Never mind that current actually flows backward from negative to positive, it's just easier to think of it the other way around.)
  4. Look at the terminals on the switch next. It is a bit more complicated, but once you understand what role each one plays, it will make perfect sense! The "Slide Switch" has two terminals, one on top "Terminal 2" and one on the bottom "Terminal 1". The third terminal in the middle called "COM" or "Common" plays a special role. It shares a "commonality" with the top "Terminal 2" and the bottom "Terminal 1".
  5. Without this "common" terminal, it would not be possible to make a three-way switch. For now, we are going to pretend that the switch only has the "Common" and "Terminal 1". This will allow us to think of the switch as a SPST (Single Pole, Single Throw) switch. The "Pole" is the "Common Terminal" and when we "throw" the switch, we will create continuity (current will flow) between "COM" and "Terminal 1"!

Step 3: Wire It Up!

In this step, we will add wire to our model to make it functional. Generally, we want to "color" the wire to indicate the role it plays in the circuit. Copper wire, no matter what the color, conducts electricity. Wiring leaving a "Positive" power terminal will be RED and wiring returning to the "Negative" terminal will be BLACK. This is just to help us "see" how the electricity is interacting with our circuit.

  1. Start by wiring up the battery "Positive" terminal to the switch "Terminal 1". Simply click on the "Positive" battery terminal and then mouse over to the "Terminal 1" on the switch. As you move the mouse towards "Terminal 1" on the switch, you will see a line generated that remains attached to the "Positive" terminal on the battery.
  2. When you mouse over the "Terminal One" on the switch, the text will pop out indicating that you can make a connection. Go ahead and click again. Congrats, you've just connected two components! The standard wire color is RED, and at this point, that is exactly what color we want the wire to be.
  3. Now repeat this process from the "COM" terminal on the switch to "Terminal 1" on the the light bulb. It will also default to RED which is what we want at this point in our circuit as well.
  4. Finally, let's finish the wiring from Terminal 2 on the light bulb to the "negative" terminal on the battery. After creating this wire, it will also default to RED. Let's change it to black to give an indication that this part of our circuit is connected to the "Negative" leg of our bulb.
  5. Click on the RED wire from the lightbulb to the battery. That will select that particular segment of wire and will provide you a way to change its color. In that drop down menu, select black and then click somewhere on the blank part of the canvas.

In the next lesson you will learn to wire a three-way switch

Next Lesson:The Three-way Switch


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