# Final Project: Secret Code Keypad

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## Introduction: Final Project: Secret Code Keypad

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

Lesson Overview:

Now we'll build a full circuit: a secret button code!

## Step 1: Introduction

For your final project, you will create a keypad that uses a secret code to turn on a light bulb.

You will use the concepts of buttons in series, and a short circuit to create a secret code keypad with three buttons. In the keypad, two buttons need to be pressed at the same time to light up a light bulb - not ANY two buttons, but a specific two buttons.

## Step 2: How Does It Work?

You will press buttons A and B at the same time to turn on the light (see diagram below).
The two correct buttons (A and B) are connected in SERIES with the light bulb. That means both need to be pressed to close the circuit. The third button (C), SHORTS the bulb so it can never turn on. It doesn't matter if you press buttons A and B - if button C is shorting the light, it can never turn on. On the schematic, it is easy to tell what buttons need to be pressed. On the breadboard, you can create a line of buttons and decide which ones are the key to your secret code. Use the instructions on the next page to create your own secret keypad!

1. Connect the left terminal of Button A to the red (voltage) rail.
2. Connect Buttons A and B in series. This means that they share connections at one terminal.
3. Connect the free terminal (that hasn\u2019t been connected yet) of Button B to the left terminal of the light bulb.
4. Connect the right terminal of the light bulb to the blue (ground) rail.
5. Stop here and try simulating your circuit by clicking the the Start Simulation button. Do you need to press Buttons A and B at the same time to turn on the light?
6. Stop the simulation to continue creating the circuit.
7. Finally, use the last button to short the light bulb. This means that the bulb and button share connections at two terminals each.
8. Simulate your circuit to see if the secret code still works! How many different combinations of 2 buttons can you press? (see hint)
9. Stuck? HINT: There are 3 possible ways to hit two buttons at a time.

The following instructions will guide you through creating your own secret keypad!

You can try wiring up your buttons and light bulbs based on the project description, or move onto the design tips in the next step.

2. Add three buttons to the breadboard spanning the gap between top and bottom sockets. Leave at least one socket empty between the buttons.
3. Add a light bulb to the breadboard, several columns away from the buttons to the right.
4. Decide which two buttons to make into the secret code. Name these buttons Button A and Button B.
5. Name the remaining button Button C
6. Press "next" to move onto the design tips in the next step.

## Step 4: Design Tips

Once you have all of the components laid out on the breadboard and labeled, use these suggestions to design your own keypad.

Remember - buttons A and B are connected in series with the light bulb and battery, and button C shorts the light bulb.

## Step 5: Your Project Is Complete!

There might be a lot of crossed wires on your breadboard. That’s ok, but can you find a way to make your circuit more organized?

Congratulations on finishing a complex circuit! If you are working with a group of students, take a look at some of their other secret keypads. Can you figure what buttons need to be pressed just by looking at the circuit?

Check out other great projects here.

## Recommendations

• ### Large Motors Class

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• ### Microcontroller Contest

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