Introduction: Hallway Bell Warning System

In school there are bells that indicate when class change should happen. They first ring to indicate when class should end, and then they ring a second time to indicate when the next class should start. If a student is late, then they usually have to get some sort of late pass. During the transition period, students may have things to do other than walking to their next time, such as going to the restroom or talking with friends, and that may lead them to be late if they lose track to time.

My device tries to inform people by acting as a clock which displays the time but also uses LEDs to indicate the time remaining.


  1. RGB LEDs (4)
  2. Adafruit 1.2" Seven Segment Display w/Backpack
  3. Arduino Micro
  4. Real Time Clock
  5. Jumper Wires
  6. Resistor
  7. PCB Board
  8. Coin Battery
  9. Micro USB Cable
  10. 3D Printer - Ender 3
  11. Filament
  12. Soldering Iron with Solder
  13. Hot glue and Hot Glue Gun
  14. Arduino IDE

Step 1: Build the Seven Segment

Follow This guide by Adafruit to assmeble the Seven Segment

After doing that bend the header pins 90 degrees towards the middle.

Step 2: 3D Print the Case

Here's the 3D modeled case for the whole device.

If you have an Ender 3 or Ender 3 pro, then put the .gcode on the mini SD Card and run the print.

If you have another 3D printer, use Cura to convert it to gcode for your 3D printer.

If you need to make any modifications, use the .ipt file to modifiy the case in Inventor if you need to.

Step 3: Wire the Device

Pre steps:

  1. Put the Seven Segment inside the case.
  2. Hot glue all the RGB LEDs onto the case.

RGB LED - should be common anode

  • Pin 9 = Red
  • Pin 10 = Green
  • Pin 11 = Blue
  • Make sure to use a resistor
    • Only need one if you put it on the GND leg of the LED (longest leg)
  • All four LEDS should be in parallel.

Pins for Serial on Arduino Micro

  • SDA - 2
  • SCL - 3

Seven Segment and Real Time Clock (RTC)

  • Both have 1 SDA and 1 SCL, are connected in parallel
  • Both Have 1 GND Pin
  • Seven Segment has 2 5V and RTC has 1 5V

Solder everything together on the PCB Board like in the picture.

Step 4: Upload Code

Make sure you have the Arduino IDE Installed.

Make sure you have these Libraries Installed:

How to Install Libraries on Arduino

1) Set the Bell Schedule (Picture 1)

  • Change the minute and hour values to suit your schedule.

2) Set the Current Time. (Picture 2)

  • Change the values in the second picture to the current time and date
  • Upload the Code

3) Re upload the Code with a modification.

  • After uploading it once and setting the time on the RTC "comment out" (which means the code won't run) the section that sets the time in the setup() loop. This will prevent the time from resetting back to the time from step 2 whenever it loses power/resets.

Clocks Contest

Participated in the
Clocks Contest