Introduction: KEY? I GOTCHA

About: I'm a student currently at Taiwan's Kang Chiao International School. My current works are based on projects assigned by the school, therefore, my project is done usually simply, and easily.

Kang Chiao International School

Name: Anderson Chou

Student Number: J05271

Class: 9D

The project is based on my personal experience. In my life, I've discovered many ways to lose my keys, therefore, in consideration of me getting scolded. I decided to build my very own key reminder where I won't forget my keys. The project presented was made for a class project, so haters back off! Anyhow, the project is easy, simple, and very reliable. In here I'll teach you how to fabricate an easy project such as mine: with 5 easy steps.

- Easy




I used a lot of materials and supplies, however, I cannot estimate how many wires I used, therefore, I would only give you the more significant parts and countable parts.

Breadboard x 1

Arduino Leonardo x 1

USB wire x 1

Ultrasonic sensor x 1

LED (green) x 1

LED (red) x 1

LED (yellow) x 1

Metal hanger x 1

Crocodile clips x 2

Aluminum foil x 3 pcs

These are the most basic ones, for more information on what sort of machines I used, you can ask me personally or email me. At


Before we start like all projects, we need to think of a problem and idea for your project. Here I used my habit of losing keys. Therefore, I started to research what type of sensors I could use to counter this habit. As a result, I chose two:

Ultrasonic distance sensor & crocodile clips

Then I brainstormed my final format and design.

Which would look like the ones above, pictures above. (There weren't any clips, so I used a button instead it's the same process)

1. To make sure everything is in place and working, I would try testing it each time you modify something new. For example, the Ultrasonic sensor I tested it for 10 times until I was sure of it. And that the LED lights did light up properly.

2. Then the routes. If one route seems unreasonable aren't working try re-routing the wires. Some may be fiddled with or some may have errors. Therefore, try not to tangle the wires so it doesn't look like a mess.


Programming is one of the hardest parts of any technology-based project. This is because one slight flaw can affect the whole of the circuit. Therefore, in programming, I used a simple program in order to reach my goal, limiting the possible fails. As a rookie in programming, I used the help from Ardublock (which I totally recommend for beginners). I processed what I needed to do and the final program is the one below.

My program:

int ardublockUltrasonicSensorCodeAutoGeneratedReturnCM(int trigPin, int echoPin)

long duration;

pinMode(trigPin, OUTPUT);

pinMode(echoPin, INPUT);

digitalWrite(trigPin, LOW);


digitalWrite(trigPin, HIGH);


digitalWrite(trigPin, LOW);

duration = pulseIn(echoPin, HIGH);

duration = duration / 59;

if ((duration < 2) || (duration > 300)) return false;

return duration; }

void setup() { Serial.begin(9600);

digitalWrite( 13 , LOW );

pinMode( 12 , OUTPUT);

pinMode( 2 , INPUT);

pinMode( 7 , OUTPUT);

pinMode( 5 , OUTPUT); }

void loop() { Serial.print( ardublockUltrasonicSensorCodeAutoGeneratedReturnCM( 13 , 12 ));

Serial.print(" ");


if (( ( ardublockUltrasonicSensorCodeAutoGeneratedReturnCM( 13 , 12 ) ) < ( 100.0 ) )) { digitalWrite( 12 , HIGH );

} else { digitalWrite( 12 , LOW );

} if (digitalRead( 2 )) { digitalWrite( 7 , HIGH );

digitalWrite( 5 , LOW );

} else { digitalWrite( 7 , LOW );

digitalWrite( 5 , HIGH ); } }

It might seem quite confusing and difficult at first, but with the help from Ardublock, it seems quite reasonable and I could easily understand it.

Step 3: Manufacturing Structure

Having a mainframe for any project adds up, as it provides not only the attraction but the outstanding achievement of just making a mainframe. As a student I used my teacher's equipment quite a lot in this project, therefore, the mainframe might not be so convenient for some users. However, every mainframe has its own unique point so just creating one yourself is a great achievement itself. In my case, I used a laser-cutting machine where I am able to design my own structure and mainframe. I used Adobe Illustrator for this particular task. The examples are in the files.

With a simple, yet useful project like this one. Use what you have...

- Cardboard

- Scissors

- Aluminum Foil

- Hangers

Are all good examples of what you can find at home. The more sufficient you are the better. AND REMEMBER TO DOUBLE CHECK AT ALL COSTS. Some people may find double-checking a nuisance, however, this does not waste materials and time. If you are further in your progress and finally see something that is out of place, it is too late. Therefore, please double-check at all cost. I learned from my experience that double-checking is the best solution.


- Glue gun

- Hardwood

- Hanger

- Aluminum foil

- Knife

- Scissors

- Computer


Step 4: Managing

After finishing the structure try fusing the two together. Since not all projects are done in one try, use what you have at first and start managing. Some lines may not fit your infrastructure, and so you have to restart your structure which is totally fine, and common. Managing is a very significant task in these kinds of project, where you can find any possible flaw and any kind of mistake. It is a section focused on double-checking before you submit a final project.


- Does the LED light up?

- Did I use an adequate amount of materials?

- Are the wires too fragile and tangled?

- Does this even work?

- How do I make this better?

- OMG! (Yes, you'll say this quite often when doing these sorts of my opinion)

- Can I score a high mark with this project?

All of the above are things you might ask yourself when fabricating projects as such. Managing is a step that everyone needs to take, to rethink, reprocess, and to reconsider. It is a step that quite dangerous and can lead you to remake the whole project. Thus, it is a very important process and step. It's very common to recreate a project. So if you'll really stuck, rethink and calm down.

Step 5: Achieve It. & Reflect It.

Now that you're done. ENJOY. Be proud of what you did and even if you did not earn a high score, be proud because only you can judge yourself, don't bother at the score. Scores are only numbers. Achievements are the only steps to success. Now that I've finished it's definitely the time to test it out. The video above is how my project works, and how I'm proud of it. As a student, it is one of my great achievements. Even though it may seem like much, but, overall, I'm quite proud. After the tough challenges I faced, I managed to pull through the toughest times.


And like what I have been doing. Share your experience to the web. To the whole world. Because IT IS YOUR ACHIEVEMENT. Reflect your self, in the future, you might look back at it and say, "oh it's actually not that bad!" or "OMG what a cringy project!" Anyhow, reflect and share what you made, and BE PROUD.


To summarize how my project works here is the text form. (While the video of how it works, is above.)

When a person opens the door the ultrasonic sensor would project you, and light up the yellow LED, indicating that it sees someone and sort of "asks you for a key". When the key isn't placed the red LED light would switch on indicating that there is a missing key. Which can later remind you that "please put the key back." When you put the key back and leaves both the yellow LED and the red LED would switch to off, since there is a key present and you are not in the area.


The ultrasonic sensor that was used is to detect any object that is within 80 cm of its range. Therefore, if a person is standing there it would detect "true". If it was above the 80 range then it would switch to "false". The LED yellow is an indication and signal of whether it detects an obstacle or not. And the red and green LED are an indication of whether there is a key or not. I used crocodile clips in this case. One clip to the box where it is filled with aluminum foil, and the one to the hanger. When a metal key is present and hangs on the hanger, the LED green would switch on. Because the metal key is a part that connects the negative charge (aluminum foil) with the positive charge (hanger), therefore, it creates a running circuit. Signifying that the key is present. When you take off the key, there are no positive and negative charges, because it does not connect which leaves the red LED light on, signifying that there is no key detected. That is the basic mechanism of my project. Please comment if you have a concern or question.

*This may sound like an inspirational website, but, no, it is actually some random project we had to do...I did it to spice things up...