Gelbert the Garbage Bin

Introduction

To disrupt the Gelber Sack culture in Stuttgart, Germany, it only takes one yellow trash bin. We introduce you: Gelbert — the yellow bin that only wants yellow trash.

At its core, Gelbert uses color detection to make a simple but dramatic decision:

if you feed it the wrong colored trash… it throws everything out onto the floor.

No warnings. No second chances.

Are you ready to build the most annoying, grumpy trash bin you’ve ever seen?

By: S. de Uría, A. Mzannar, P. Houwald

Supplies

Electronics & Control

1. Arduino Uno + Cable to USB port
2. Small Breadboard
3. 9V Battery
4. Jumper wires (plenty of them)
5. Mini DFPlayer for Audio Decode
6. SD Card

Sensors (Input - What Gelbert “sees”)

1. Ultrasonic Sensor
2. RGB Sensor

Actuators (Output - How Gelbert “reacts”)

1. X2 Mini Servo Motors
2. Mini Speaker 3W
3. Liquid Crystal Display (LCD) 16x2 Screen

Mechanics

1. Cardboard box pieces
2. 3D printed Gears
3. Wooden Dowel (⌀ 98mm)
4. Duct Tape (lots of it)
5. And some extra cardboard just in case
6. 
   

Prettiness

1. Thin Yellow Cardboard
2. Googly eyes (⌀ 35mm)

System Overview

So how does Gelbert actually work?

The main trick behind the design is the additional top flap inside the bin. This is where the two sensors are mounted, allowing Gelbert to detect what kind of trash you’re offering.

If Gelbert likes the trash (i.e., it’s yellow), everything goes smoothly: the top flap opens, and the trash simply drops down into the bin. But if the trash is not yellow… that’s when the nightmare begins.

Instead of accepting it, Gelbert reacts dramatically: both the top flap and the bottom flap of the bin open at the same time, dumping all the trash onto the floor — including everything that was already inside.

To make sure you understand your mistake, the screen and speaker loudly express how upset Gelbert is about your poor life choices.

A button allows you to close the bin again and reset the system — so you can try once more…

Just make sure not to repeat your mistakes!

Logic Diagram

In other words, Gelbert’s behavior can be described in three simple states:

A sensing state, where proximity and RGB values are detected

An actuation state, where the LCD, motors, and speaker are triggered

A waiting state that allows the fully open bin to be reset before restarting the loop.

Overview of Circuit

Before putting everything into the bin, it’s important to build and then test the full circuit. This makes troubleshooting much easier (and avoids tearing apart your masterpiece later).

Use the circuit diagram below to guide your assembly.

Sensors

Let’s start by connecting the Arduino 5V and GND to the breadboard. This will be our main circuit, where most components are powered from.

Next, connect the ultrasonic sensor to the breadboard and to the Arduino's correct pins (VCC, GND, TRIG, and ECHO).

For the RGB sensor, we need a lower voltage. Connect it directly to the Arduino’s 3.3V (3.5V) and GND pins. Make sure to connect SDA → A4 and SCL → A5

Finally, connect the reset button to A0 and GND on the breadboard.

Your sensors are now fully connected!

Actuators

Now connect the 2× servo motors. The lower flap servo should be connected to Pin 10, and the upper one to Pin 11.

For the LCD screen, the wiring is a bit more complex. Make sure to carefully follow the circuit diagram and your Arduino code to connect all pins correctly. To control the screen’s contrast, don’t forget to use a potentiometer on the V0 pin.

Finally, connect the speaker using the DFPlayer (MP3 module). Insert an SD card with your audio file, and connect the module to the Arduino (TX/RX). Make sure to use resistors on the RX/TX lines to ensure stable communication.

Arduino Code

Great — if you made it this far, you’re almost done!

Now connect your Arduino to your computer and upload the code to the Arduino Uno. We included a few Serial print statements, so you can monitor what’s happening and quickly spot if something is wired incorrectly.

You have a fully functional sensor–actuator system. Yay!

Cardboard Bin

The last part is by far the most challenging: you now have to fit your nicely assembled circuit into a box and make sure all mechanical parts work smoothly.

Start by preparing the cardboard box. Cut it so you have an open top, a movable bottom flap, and an open back (think of it as a deconstructed shoebox).

Cut a hole in the front for the LCD screen, add two symmetrical holes on the sides for the wooden dowel (this will rotate the top flap), and make a small hole in one bottom corner for the button.

Insert the 3D-printed frame support at the bottom of the box; this adds stability and helps attach the lower motor later.

First, assemble the ultrasonic sensor and the screen inside the box. At this step, you can also place the Arduino and the breadboard inside, so all the large components are already positioned. Secure everything using duct tape (lots of it).

Now assemble the top flap. Cut a hole so you can later wire the RGB sensor through it, and attach the cardboard piece firmly to the wooden dowel. Add the gear to the wooden dowel and insert the dowel through the side holes. Make sure to align the top servo motor so the gears engage properly.

Next, assemble the mechanism for the bottom flap. Mount the second servo motor, attach the 3D-printed lever, and make sure to align the latch mechanism so it opens and closes cleanly.

Final Check

Let’s do a final check: make sure no wires block the moving parts. Close the final side of the box once everything is tested and secured. Slightly shake the box to check if the components are secure — if something moves, add more tape :) For Gelbert version 2.0, we promise a more sophisticated assembly strategy…

Wrap Gelbert with the thin yellow cardboard, tape Gelbert’s feet, and attach some googly eyes — and voilà!

Have fun with Gelbert!