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Project Name:	Simple Switch Circuit
Project Description:	Learn how to make a simple switch circuit.
Difficulty:	Easy

In this project, we’re going to make the basic and simple switch circuit. Having a switch in your circuit allows you full control of your circuit. A switch allows you to turn ON or turn OFF the entire circuit or even just parts of a circuit.

For this project, a simple push-button switch will do the trick of turning our circuit ON or OFF. If you’d like, you can try whatever appropriate switch you’d like to control your own circuit — experiment and have fun!

Description of Items Needed for Switch Circuit

To build our simple switch circuit you need just 7 items:

1. 1 x Breadboard: The breadboard helps us put the circuit together without soldering. Easy-peasy.
2. 1 x Red LED: We’ll use an LED as an indicator in our circuit. It will show us that our circuit is complete and working when it turns ON after we turn the switch into its ON position.
3. 1 x 390 Ω Resistor: We need the 390 Ohm resistor to help “slow down” or limit the current in our circuit before it gets to the LED. Doing so protects the LED from wear-and-tear or damage from too much current flow.

4. 1 x 9V Battery: A 9-Volt battery serves the purpose of providing the power we need to energize our circuit to turn the LED ON.
5. 1 x 9V Battery Snap Connector: We need a 9-Volt battery connector to connect our 9V battery to our circuit. If you don’t have a 9V battery connector, you can use alligator clips. To learn how to attach a 9V battery to a breadboard using alligator clips, watch this video here.

6. 1 x Switch: I’ll show you several different scenario circuits with different switches so that you can choose whichever you’d like to try, or try them all! We’ll demonstrate the switch circuit with the following switches:
   • Push-Button Switch
   • Slide Switch
   • Rocker Switch
   • Toggle Switch
7. Jumper Wires: We’ll use jumper wires to help us connect our components together in our circuit on the breadboard.

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Parts List

Item	Quantity	Description
Solderless Breadboard	1	This allows us to put the circuit together without soldering.
Red LED – 5mm Diffused	1	This will serve as our indicator light to tell us whether the circuit is ON or OFF.
390Ω Resistor	1	We use this to limit the current through our LED.
9V Battery	1	This is our power source.
9V Battery Snap Connector	1	This makes connecting our battery to the circuit easier.
Switch	1	Controls the ON/OFF operation of the circuit.
Jumper Wires	Multiple Miscellaneous Sizes	We use these to make solderless connections to our components on the breadboard.

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Step-By-Step Process

Now that we have all the items we need, it’s time to build our switch circuit! Below is an easy to follow, step-by-step process that’s clear and concise to help you successfully complete your circuit. For this process, we’ll be using a push-button switch. Other switches will be represented for this same circuit later in this blog post under “More Switch Circuits!“.

Push-Button Switch Circuit

The push-button switch works by pressing a button down to make a metal contact complete the circuit, therefore turning ON the LED. When you release the button, the contact is released and the circuit becomes open, therefore turning OFF the LED. The following steps explain how to create your own push-button switch circuit:

1. First, have your breadboard ready; clean and clear of any wires and components from previous circuit builds you may have placed on your breadboard. We want to start from scratch on our breadboard.

2. We need to get our breadboard setup for power and ground. We first need to make a positive (+) terminal and then a negative (-) terminal:

3. Next, grab your push-button switch and place it on your breadboard as shown in the following image:

4. Now, take the 390 Ω resistor and place it as shown in the video for step 4 below [Note: The resistor orientation does not matter]:

5. Next, we place the LED’s anode (+) in contact to the resistor lead opposite of the switch, and then the LED’s cathode (-) to the negative terminal of the breadboard, as shown in the video for step 5 below:

6. Now, take a jumper wire and connect one end of the jumper wire to the switch terminal and the other end of the jumper wire to the positive terminal, as shown in the video for step 6 below:

7. Let’s now connect our 9V battery to the 9V battery connector. It’s easy! Connect the positive post of the 9V battery to the snap of the connector that fits its size and then, connect the negative post of the 9V battery to the snap of the connector that fits its size, as shown in the video for step 7 below:

8. Now its time to hook-up the power! Take your positive lead of the of the 9V battery connector and put its end into the positive-side (+) terminal we’re using for our breadboard. Next, connect the negative lead of the 9V battery connector and put its end into the negative-side (-) terminal we’re using for our breadboard. NOTE: In the supplemental videos for the steps above, the battery snap connector was already shown connected to the breadboard.

• If you don’t have a 9V battery connector and are using alligator clips instead, then:
  • take one red alligator lead and connect one of its alligator clips to the positive terminal (+) of the battery and the other end to the positive terminal (+) jumper wire on the breadboard.
  • Take one black alligator lead and connect one of its alligator clips to the negative terminal (-) of the battery and the other end to the negative terminal (-) jumper wire on the breadboard.

• Finally, press the push-button switch down and see what happens. Did your LED turn ON?

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Frequently Asked Questions

Q1.) My LED did not turn ON! What do I do now?

1. Make sure you connected the leads of the battery connector correctly. Positive (+) lead to positive-side terminal of breadboard. Negative (-) lead to negative-side terminal of breadboard.
2. Make sure the orientation of your LED is correct. The anode (+) toward the lead of the resistor and the cathode (-) of the LED to ground or negative-side bus of breadboard.
3. Make sure your jumper wires or any component leads are connected end-to-end properly in the breadboard points.

4. Make sure your switch is not placed in such a way that the circuit cannot be complete. The push-button switch is placed crossing the center groove of the breadboard in our circuit above in step 3. On either side of this center groove, the points on the breadboard are not connected. If you have placed your switch in a way that doesn’t complete the circuit, go ahead and place the switch and any other components or jumper wires as shown in the steps provided above or take a look at the supplemental video below:

Q2.) My LED is ON, but stays ON. It won’t turn OFF! What do I do?

1. The reason why your LED is ON and stays ON without the influence of the switch keeping it ON or OFF may be due to a short in your circuit. Make sure you have properly connected your components on the breadboard. Go back over the steps and their provided images above. Also, see the solutions to the FAQ question about “My LED did not turn ON! What do I do now?”, to see if it helps you out.
2. Make sure your switch is not placed in such a way that the circuit is shorted because of it. If you have placed your switch in a way that completes the circuit, but doesn’t allow for any switch control, go ahead and place the switch and any other components or jumper wires as shown in the steps provided above or watch the supplemental video below.
3. Though rare, you may possibly have a faulty or damaged switch that’s causing a short. Grab a new one and insert it into your circuit to see if this was the problem.

Q3.) How do we know what size resistor to use in our circuit?

• We use Ohm’s Law!
• Ohm’s Law states that voltage (V) is proportional to the product of current (I) and resistance (R):

Ohm’s Law \begin{equation}\label{eq:NL}
V = IR
\end{equation}

• The LED in our circuit provides a forward voltage drop, meaning there’s some resistance from the LED itself creating a forward voltage drop across it.
• The forward voltage is when current is traveling in the correct or forward direction of the LED to allow current flow (an LED is a diode), and when the rating of the forward voltage is met (let’s say, 2.1V), then this allows the LED to light up.
• So, our LED has to have at least a 2.1V forward voltage drop across it to light up.
• A typical forward voltage drop of a red LED is between 2.1 and 2.4 volts at 20 milliamps. So, we’ll be making a couple of assumptions here:
  1. We’ll assume a voltage drop of 2.1 volts across the LED.
  2. We’ll assume our circuit current is 20 milliamps.
• Since there’s a forward voltage drop from our LED, we’ll consider the fact that there’s a change in voltage in our circuit from the 9V battery source to the voltage drop across the LED. We represent the change in voltage as:

\begin{equation}
{\Delta V}
\end{equation}

• The Δ in front of the V is the capital Greek letter “delta”. The capital delta (Δ) is used in mathematics to represent a change in values. So ΔV here, in this context means “the change in voltage”.
• Since our entire circuit is a series circuit consisting only of a battery, a resistor, and an LED, there is no change in current, since the value of current within a series circuit is the same. So, we’ll still represent current with its symbol:

\begin{equation}
I
\end{equation}

• So, as of right now we want to represent Ohm’s Law in the following manner:

\begin{equation}
{\Delta V} = IR
\end{equation}

• If we need to find the value of the resistor in our circuit, all we need to do is divide both sides of the equal sign in Ohm’s Law by the current (I) to obtain the rearranged equation:

\begin{equation}
R = \frac{\Delta V}{I}
\end{equation}

• Now, we just substitute our values into our equation above:

\begin{equation}
R = \frac{\Delta V}{I} = \frac{9V – 2.1V}{20mA} = \frac{6.9V}{0.020A} = 345Ω
\end{equation}

• Since I don’t have a resistor valued at 345 Ω I chose a resistor value slightly above it at 390Ω, which will do just fine.

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More Switch Circuits!

The following switches can be used in your switch circuit build from above. All you need to do is remove the push-button switch from the previous circuit build and replace it with your switch of choice. Said another way; the process is the same as the push-button switch circuit, it’s just that the switch used in the circuit is different.

Slide Switch Circuit

• The push-button switch turned the LED ON in the previous example circuit by pressing the button down to make a contact complete the circuit. When you let go of the button, the contact was released and the circuit became open, therefore turning OFF the LED.
• The slide switch works differently than the push-button switch. When you move the slider on the slide switch one way, the LED turns ON and stays ON. When you move the slider on the slide switch the other direction, it turns the LED OFF and it stays OFF.
• Using the same steps as we did for the push-button switch, for step 3, put the slide switch in your circuit in place of the push-button switch as shown in the video below.
• Turn your switch ON by moving the slider on the slide switch. Depending on how the slide switch was attached, the LED might have come ON without you moving the slider on the slide switch. That’s OK. Just move the slider the opposite direction to turn the LED OFF. You should be able to turn the LED ON and OFF by moving the slider on the slide switch one way or the other.

Rocker Switch Circuit

• The rocker switch works on the same principle as the slide switch, in that there’s contact made in the circuit by moving the metal contact to one side of the switch or the other.
• The rocker switch works by “rocking” the switch to one side or the other to close or open the circuit.
• Using the same steps as we did for the push-button switch, for step 3, put the rocker switch in your circuit in place of the push-button switch as shown in the video below:

Toggle Switch Circuit

• The rocker switch works on the same principle as both the slide switch and rocker switch, in that there’s contact made in the circuit by moving the metal contact to one side of the switch or the other.
• The toggle switch works by “toggling” the switch to one side or the other to close or open the circuit.
• Using the same steps as we did for the push-button switch, for step 3, put the toggle switch in your circuit in place of the push-button switch as shown in the video below:

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Conclusion

You have just completed making your own simple switch circuit! You were able to take a few simple components, place them in your breadboard, add power, and control an electronic device, like an LED. You should be proud of yourself.

In our example switch circuit we controlled an LED, but you can replace the LED with whatever device you’d like, such as a:

• buzzer,
• DC motor,
• fan,
• and others!

Try it and experiment with your circuit. Doing so will help you understand circuits more and how they function. There’s not much of a better way to learn something than by doing it!