Introduction: Door Warning Stop Sign

About: @HeyReynolds

My classroom door opens into the hallway without a window. This design flaw ends up with a consistent fear of opening the door into the face of students walking to class. Some poor student who isn't looking gets hit almost every day. So I began brainstorming a simple way to alert students the door was about to swing open. The hallways are too loud to use a sound device, so I decided on a flashing stop sign design, much like a railroad crossing. So using an Arduino, 3D printer, a few LEDs and magnets I was able to put together a great little device to help prevent student concussions!


You'll need--

3D printer and files here... (Thanks to Lolitstony for making and sharing this stop sign design. I was able to scale it and design a back compartment for it.)

8 LEDs, any color, I used red.

Ribbon cable from Amazon

Neodymium Magnets from Amazon

Project Box

Arduino & breadboard

USB Cable

Phone Charger

Micro Limit Switch from Amazon

White Paint

Step 1: Creating a Back Compartment

Download and print out the design from Thingiverse or create your own sign. Thanks again to lolitstony for the design. Once I had the physical object printed out, I designed a backing compartment to house the LEDs and wires. I wanted it to just snap on without adhesive or anything in case I needed to take it apart. This was was easier to do when I could measure the actual part. I was also limited to about a 6.5" diameter due to the area of my Cetus 3D printer. But it came out great and snapped right on. Here is a link to the backing part on Thingiverse-


Step 2: Painting and Drilling

You'll want to paint the white portions first, don't want to get paint on the LEDs. I used a small brush and just painted the letters and the boarder to make it stand out. Notice in the pic, red letters on red background doesn't look very good. Then I measured the LEDs accurately with a micrometer and found a drill bit the same size. With just a hand drill, I put a small hole in each corner and glued in one red LED. Try to keep an eye on which way they are facing and keep all of them the right way so wiring later is easier.

Step 3: Programming and Bench Testing the LEDs

Using an Arduino and breadboard I put together a simple array of LEDs and wired each to the output side of the Arduino. I did attempt an pizo alarm as well, but it just wasn't audible, and definitely wouldn't work in the hallways.

Here is the code for the "Chasing lights"

Chasing door warning Turns on an array of LEDs when the hallway door opens as a warning to students.

Rich Reynolds 5-14-19

Version 1.0


int pinsCount=10;

int pins[] ={2,3,4,5,6,7,8,9,10,11};

const int buzzer = 12; //buzzer on pin 12

void setup()


for (int i=0; i

void loop()


for (int i=0; i 0; i=i-1)


digitalWrite(pins[i], HIGH);


digitalWrite(pins[i], LOW);



tone(buzzer, 500);




tone(buzzer, 750);





I decided to challenge myself by programming a chasing light system rather than just having them light up or flash or anything. It actually looks really cool as they light up. Should be able to catch a students attention.I left the buzzer in the code if you want to try it...

Step 4: Wiring and Wire Management

Once the code makes the LEDs light up in the correct order, youll need to connect everything and fit it into a project box. I attached as much as I could to the lid of the box and mounted the Arduino to the bottom of the box.

The ribbon cable is important to fit through the door jam, but not get pinched when the door closes. Check your door before you mount it. Mine had enough room for a thin ribbon. Also, the colored cable will help you identify which wire goes to which LED and will make wiring easier.

To operate the device I wired in a micro limit switch to kill power to the LEDs when ever the switch is pressed/door closed. The Arduino still gets power.

Step 5: Make the Project Box

I pulled a cheap plastic project box I had on the shelf that was able to fit the arduino. I used a laser to cut some of the openings- one for USB to the Arduino and another for a battery pack to test the system on site. Once it was installed, I was able to remove the battery pack all together and run it completely off USB.This is where the phone charger is used to give it power 24/7 from the wall outlet.

I wasn't able to use the laser to cut the hole for the limit switch. I feel like a bit of a hack using a dremel to make the opening the right size and shape, but it worked... Add a few small screws to mount the limit switch.

Also added a slot for the ribbon cables to come out of the box.

Step 6: Mounting on Site!

Lastly I brought the project to school to mount to the door. I have a steel door jam, so I glued a few magnets to the box. This allows me to adjust how close it mounts to the door to ensure the limit switch hits at the right time. I fed the stop sign through the gap in the door when it was open and used poster putty to stick it to the door. It doesn't weigh much so its been working well. You can certainly just screw it to the door or use more magnets to stick it to the door if its magnetic. My doors are wood, so poster putty works fine.

Good luck! Maybe this will help all of us be a little more careful and help warn passers-by that they are about to get a face full of door. Enjoy!