Build a Simple Circuit From a Pizza Box (No Soldering)

I learn best through tactile teaching methods. Teaching and learning basic circuits, electronics, and electricity from books is good, but why not build a simple circuit from scratch and learn from doing. This is a great way to get hands on and teach/learn the basics of electricity. With this project you can change the path of the electric current to run through different sensors. With this design you can switch between lighting a Blue LED or activating a Buzzer. You also have the choice of using a Light Dependent Resistor with the LED or Buzzer. You can be creative and design your own circuit and add different sensors (other LEDs...).

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Step 1: Parts

Here is a list of the parts needed for this project:

1 - Pizza Box/Cardboard (I used the bottom of a pizza box. Make sure it is clean.)
1 - White or Blue LED (I would stay with those 2 colors because they can handle 3 volts, other colors would need a resistor.)
1 - Piezoelectric Buzzer
1 - LDR (Light Dependent Resistor)
1 - 3 Volt Button Cell Battery
~ 25 Metal Brads (I used large brads, small would work too.)
~ 20 Paperclips
Small Nail (or something to poke holes in the cardboard)
Tape (I used black electrical tape on the underside and white tape to hold it closed.)

Step 2: Lets Get Started

You can feel free to change this design and make it bigger or smaller, with more parts or less, but I am going to explain how I made mine.

First, prep the Pizza Box. I had a clean pizza box and cut out the bottom square. Then you can use the edge of a table to fold it in half.
The idea here is to use brads and paperclips as your wire.
Power! Pick the place on your board where you want the battery. Place a paperclip on that spot and with the nail poke holes just inside the ends of the clip. Then rotate the paperclip 90 degrees and poke 2 more holes. (see pic) Push a brad through the left hole and another brad through a paperclip and through the right hole. Now flip the board over.
Now on the back side place a paperclip over the 2 brads and secure it by flattening them out. This is your negative connection. (see pic) Place tape over the brad pins.
Put brads in the top and bottom holes. The top needs a paperclip on the front. on the back you are going to sandwich the battery between the clip going left right and one going top bottom. Make sure the battery is in the right way (positive is facing you and touching the top and bottom pins.
Now secure it by spreading the brad pins and applying tape. (see pic)
Your battery is now set
Flip over the board so you see the front and test the clips with the LED. (The longer LED leg is positive)
If the LED lights you can move on.

Step 3: The Switch

The first paperclip coming off the positive pin (the top brad) can be used as a ON/OFF switch. So with that clip pointing up the board poke a hole through the end of it. Move it to the side and place a brad through another paperclip in the hole you just made.
Now extend the "wire" continuing this process of lining up the paperclips, poking holes with the nail, adding another paperclip and brad. (see pic)
By now you should have gotten the idea of how to extend the "wire" by fastening the paperclips down with the brads. If not, the pictures should help.
You have just made a SPST switch. (Single Pole Single Throw)

Step 4: Choose the LDR?

Now you can make another switch to let you decide to use the LDR or not.
This is a SPDT switch. (Single Pole Double Throw)
With your last paperclip pointing up the board poke holes on both side of it and place in brads with paperclips. The clip on the left should be pointed up with a brad in the end with no other paperclip.
Just after the last brad poke 2 holes for the LDR, then 1 more hole beyond that for another brad and paperclip. Install the leads of the LDR in the holes between the brads and flip over. (see pic)
Before you lay down the brad pins, wrap a lead from the LDR around each brad so they connect. (see pic)
Then connect that top paperclip with another brad and paperclip to the other side of the switch. (see pic)
So this 3rd paperclip sticking out will be yet another switch.

Step 5: Choose LED or Buzzer

This is another SPDT switch.
Each side will have a sensor. The left will be a LED and the right a buzzer.
This is constructed much like the last step.
Place a brad on ether side of the paperclip switch.
Poke a larger hole for the LED above the left brad and from the bottom stick the lens in the cardboard.
The LED needs to be installed the right way. The positive lead/wire is longer than the negative wire. Now wrap the positive lead around the brad leg below it and the negative lead gets wrapped around the brad leg above it. (see pic)
The other side of the switch has the same thing happen, but with the buzzer. Poke 1 hole near the right side switch brad and pull both wires from the buzzer through it. You may need to strip a bit more off the wire ends. Wrap the red wire end around that "switch" brad and the black wire can go around any brad that is beyond the LED. (see pic)
Use a bit of tape folded over to stick the buzzer to the board.
It should look something like the pictures.

Step 6: Now Connect and Test

Almost Done!
Now the negative side the LED and Buzzer should be connected to the top of the last "wire chain."
Just add more "wire" to connect the sensors negative side down to the negative side of the battery. (see pic)
You are going to want to add tape to the legs of the brads on the underside to make sure nothing shorts out. (see pic)
To use the switches move them over and pick it up a bit to place on the connecting brad.
Test and make sure it works. Connect the first switch "ON." Then connect the "No LDR" side. Then choose the LED. It should light. Now choose the Buzzer and it should make noise. Leave that there and now choose the LDR and wave your hand over it or shine a light at it. The pitch of the buzzer should go up and down.
Great Job!!!
Now that it is working. With the cardboard folded, tape the edges together.

Step 7: Coloring Time

If you like you can add electrical symbols to your board, add arrows to the switches, and label the parts you used. (see pic)
I used colored Sharpie markers.

Step 8: Troubleshooting/Questions/More Info

If you can't seem to get it to work, it could be one of these things...

The battery is dead. Get a new one.
The battery came loose. Tape it in there good.
There is a short. Look on the back and make sure there is no metal tabs or pins that have rotated and are touching anything else metal that it should not be. That is why I taped all the brads on the inside.
There is a loose connection between the paperclip and the brad. Make sure the brads are bent down hard and tight.
There is a loose connection on the switch. It may help to make the moving paperclip be below the other paperclip it's connected too.
Wrong polarity. This could be that the battery, LED, or the Buzzer are in backwards.

What is a LDR?

LDR stands for Light Dependent Resistor. It resists the flow of electricity depending on how much light is shined on it. The more light the more it allows electricity to pass through. The darker it is by the sensor, the less electricity is passed through. This is why you can use this to dim the LED and change the pitch of the Buzzer.

What is a LED?

LED stands for Light Emitting Diode. It is a diode meaning it only allows electricity to pass through in one direction. There are normally 2 ways to tell the positive and negative side of a LED. The positive side has a longer lead/wire and the negative side has a small flat notch on the edge on the lens, It also glows one wavelength of light. The different color LEDs have different elements in them that make them glow their color. It is not the color of the lens that colors the light. This is why you can have clear lens LEDs.

What is a SPST Switch?

SPST stands for Single Pole Single Throw. This is a common "On/Off" only switch. It can connect the electricty from one wire to only one other wire. There is one SPST switch in this project.

What is a SPDT Switch?

SPDT stands for Single Pole Double Throw. This type of switch can connect one wire to one of two other wires. It can connect the electricty from one wire to only one other wire. There are two SPDT switches in this project.

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