Introduction: The Three-way Switch
Step 1: Adding a Second Switch
Now that you have successfully wired up a light bulb, a single switch and a battery, let's add a second switch to break down how a three-way switch works like the ones you might have in your home.
• Reminder that we used an SPDT (Single Pole Double Throw) switch as a SPST (Single Pole Single Throw) switch in the previous lesson by not using the additional terminal.
- Remove all the wires from the canvas. You can do this by making sure to "stop simulation", if you are still running it, and then "clicking" each wire and hitting the "delete" button on the keyboard. The canvas will look sort of like this when you are done.
- Add an additional SlideSwitch to your canvas and arrange the various components as demonstrated in the image. You will need to use the rotate button again to orient it correctly.
- Remember, we used the SlideSwitch in the previous lesson as a SPST switch by not using the additional terminal. When the switch was positioned such that the "powered" terminal and the "COM" (common terminal) were shorted, current would flow and the light bulb would light up.
Step 2: Wire It Up!
Now that you have laid out all the components, let's wire it up.
• Clarification on how an SPDT switch works.
• Importance of using color schema for your circuits.
RED wire for positive voltage (V+) BLACK wire for negative voltage (V-) GREEN wire for ground (GND)
- Let's power up the COM terminal on the first switch. Click on the "Positive" terminal and then click on the COM of the first SPDT switch.
- Now let's connect the COM terminal on the second switch to Terminal 1 on the light bulb. Let's also make sure this wire is RED. (Red should be the default color for wire when you add it.)
- Now that we have wired up the "Positive" leg of our circuit, let's add the returning "Negative" leg. Click on the "Negative" battery terminal and then click on Terminal 2 of the light bulb. Because the wire will default to RED, we will want to click to select it, and then change it to BLACK in the drop down menu.
- How the wire colors help: By using different colors with the wiring, the current of your circuit will be more easily understood and act as a visual guide to others looking at your work. It is traditional to use RED wire to indicate positive voltage (V+) and BLACK wire to indicate negative voltage (V-). On a traditional bread board, the other standardized wire coloration is GREEN wire for ground (GND)
- Now that we have the general path that current will follow added by wiring up everything but the two switches together, let's see how we can make the magic of the three way switch a little less magic and a little more understandable.
- Let's start by adding a wire between Terminal 1 on the bottom switch to Terminal 1 on the top switch. Do this by clicking in Terminal 1 on one switch and then clicking on Terminal 1 on the other. Once the RED wire is in place, click on it to change it to a different color. Let's make this one ORANGE.
- Once you have completed this step, it may be interesting to see what happens if you test it. You can test the "simulation" at any point by clicking the "Start Simulation" button in the upper right corner. Go ahead and try it now. See if you can get the light bulb to come on and note the state of each switch when you do.
- Ok, let's go ahead and stop the simulation by pressing the "Stop Simulation" button. If you are like me, you probably thought back to the previous lesson where you only had one switch, and that the light only came on when you shorted the circuit across Terminal 1 and COM. The same is true here, but in order for it to work, both switches had to be shorted the same way. No mistake there! That is necessary in order for the current to have a path to follow. If one switch is shorting the correct terminal, and the other is not, then there is no path for the current to follow, thus the circuit is left "open" and the current can not flow.
- Let's complete the three-way switch. Go ahead and add the last wire. Click on Terminal 2 on one switch and then Terminal 2 on the other. Once that RED wire is added, let's click on it and make it PURPLE.
- Now that we have a completely wired system, let's test it out! Go ahead and start the simulation again. In all likelihood, your circuit will already be closed and the light bulb will be lit. Go ahead and change the state of the lower switch so that the light goes off.
- Now that you have an unlit bulb, image you find yourself at the bottom of a staircase, and you need to go upstairs. Turn the light on from the bottom of the stairs and imagine you have climbed the stairs. Now that you are at the top of the stairs, imagine you need to turn the light off. By changing the state of the switch at the top of the stairs, you open the circuit again and the light goes out. This is the same way a similar switch in your house might work! Congratulations on completing this project!
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