Smart Compost Bin – Our Journey from Idea to 3-Layer Smart Design

Team The Rot Squad:

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Published August 2, 2025

Odour-free smart compost bin for urban flats

Smart Compost Bin: A compact, odour-free bin for urban flats that automatically composts kitchen waste and sends real-time alerts.

BeginnerFull instructions provided86

Odour-free smart compost bin for urban flats

Things used in this project

Hardware components

ESP32-WROOM-32

DHT11 Temperature & Humidity Sensor (3 pins)

MQ 135 Air Quality/Gas Detector Sensor Module

Seeed Studio 12V DC Water Pump

SparkFun Dual H-Bridge motor drivers L298

Geared DC Motor, 12 V

SparkFun Soil Moisture Sensor (with Screw Terminals)

SG90 Micro-servo motor

Exhaust fan(5V)

Breadboard (generic)

Jumper wires (generic)

12V POWER ADAPTER

Software apps and online services

Blynk

Arduino IDE

Story

Smart Compost Bin – Our Journey from Idea to 3-Layer Smart Design

where it all began

It started with a simple thought: Why can’t urban flats compost kitchen waste without the smell and hassle?We picked up a pen, made our first sketch, and the journey began.

Our basic concept:

3 compartments separated by 2 flipping lids
Waste drops layer by layer using servo motors and gravity
Goal: A compact, odor-free, automated composting solution

Primary Design: First Prototype

A container with 2 flipping lids.
Waste is disposed into the first compartment.
Servo motors flip the lid to move waste to the next compartment.
WasteTransfer Flow:
First lid flips → Waste to second compartment
Second lid flips → Waste to third compartment
First Axis Concept:
Lids rotated around an axis through the center, splitting the circle into two equal halves.

Principle:

Flipping the upper lid transfers waste to the compartment below.

Challenges We Faced

Complex Flipping Mechanism
Needed 4+ servos:
2 for flipping
2 for locking
Increased cost, power draw, and complexity
BladeInterference
Second compartment had mixing blades
Flipping the upper lid caused waste to hit the blades, blocking smooth transfer

Solution: Latch & Counterweight Mechanism

1 / 2 • The solution

After trial-and-error, we came up with a simpler, smarter solution:

Axismoved to 1/3 of the diameter of the lid
Counterweight on smaller section balances the heavier waste side
Stopper & servo lock control flipping:
Servo locks lid until waste is added
Servo releases, lid flips, waste drops
Counterweight swings lid back up, caught by stopper

Result:

Fewer servos
Smooth waste transfer
No interference with blades

Evolution to the Final 3-Layer Smart Compost Bin

1 / 11 • final setup

We transformed our idea into a compact, 3-layer automated composting system:

Inner Bin (3 Layers)

Layer1 – Input Layer
Food waste + inoculum added
Porous bottom drains excess water to leachate compartment
Layer 2 – Active Composting Layer
Waste mixed with blades for aerobic composting
Sensors monitor temperature, humidity, and gas levels
Layer 3 – Final Compost Storage
Collects dry, odor-free compost

Leachate Collection Compartment

Collects liquid (leachate) from Layer 1
Prevents waterlogging & anaerobic odor
Can include tap or sensor for easy draining

Sealed Outer Enclosure

Keeps system odor-free and safe for indoor use
Exhaust fan + carbon filter for clean airflow

ESP32 + IoT Smart Control

(Insert Wokwi wiring diagram and prototype image)

Our solution is a compact, three-layer smart compost bin for urban flats, using ESP32 and sensors to automate composting. It:

Monitors temperature, moisture, and gas levels
Triggers mixing and moves waste via servo-based latch system
Controls odors with a carbon-filtered exhaust fan
Sends real-time alerts via Blynk app (refill, drain, collect compost)

This low-maintenance, odor-free system efficiently turns kitchen waste into compost, supporting SDGs 11, 12, and 13.

Working Principle

Waste is added to Layer 1 → excess water drains
Servo-based lid flips → Waste moves to Layer 2 for active composting
Mixer motor & fan maintain aerobic, odor-free conditions
Leachate tank collects liquid
Sensors + ESP32 monitor conditions & send alerts
Final compost collected from Layer 3

Build & Testing Journey

1 / 7

Started with breadboard & servo tests
Solved lid flipping and odor issues with latch system + carbon filter
Integrated sensors + IoT for real-time alerts
Final prototype: Compact, automated, and urban-friendly

Results & Impact

Odor-free automated composting in urban flats
Minimal manual effort → Add waste, drain leachate, collect compost
Eco-impact:
Diverts 60–100 kg of waste per flat/year
Reduces methane emissions from landfills

Future Scope

Compost quality sensing (NPK levels)
Solar-powered & fully off-grid version
App dashboard for RWAs & smart cities

Conclusion

Our Smart Compost Bin turns everyday kitchen waste into eco-friendly compost, making urban flats sustainable, odor-free, and part of the green revolution.

Circuit diagram simulated in Wokwi

Circuit Diagram Description
The Smart Compost Bin circuit is built around an ESP32 Dev Board that controls all sensors and actuators:

Sensors

DHT22 measures temperature and humidity of the composting chamber (Data → GPIO 4).

MQ2 Gas Sensor detects VOC/gas buildup (Analog → GPIO 34).

Potentiometer simulates the soil/moisture sensor for testing (Analog → GPIO 39).

Actuators

3 Servo Motors (GPIO 15, 13, 14) control lids for transferring waste between layers.

Mixer Motor, Exhaust Fan, and Relay Output are simulated using LEDs:

LED on GPIO 25 → Mixer Motor ON/OFF

LED on GPIO 27 → Exhaust Fan (always ON in code)

LED on GPIO 32 → Relay Signal (simulates auxiliary control)

Power Connections

ESP32 VIN/5V → Red rail (Powers servos, MQ2, DHT, and LEDs)

ESP32 GND → Black rail (Common ground for all components)

Potentiometer powered from 3.3 V for stable analog input

Simulation Note

LEDs are used in place of DC motors, exhaust fan, and relay module since Wokwi does not support these components.

In real hardware:

GPIO 25 drives Mixer Motor via L298N

GPIO 27 drives Exhaust Fan via L298N

GPIO 32 controls Relay Module

Code

Code uploaded to ESP-32

 #include <ESP32Servo.h>
 #include <DHT.h>
 #define SERVO1_PIN 15
 #define SERVO2_PIN 13
 #define SERVO3_PIN 14
 #define MIXER_IN1 25
 #define MIXER_IN2 26
 #define FAN_IN3 27
 #define FAN_IN4 33
 #define RELAY_PIN 32
 #define DHTPIN 4
 #define DHTTYPE DHT11
 #define GAS_SENSOR_PIN 34
 #define MOQ_SENSOR_PIN 39
 Servo servo1, servo2, servo3;
 DHT dht(DHTPIN, DHTTYPE);
 void setup() {
  Serial.begin(115200);
  dht.begin();
  servo1.attach(SERVO1_PIN);
  servo2.attach(SERVO2_PIN);
  servo3.attach(SERVO3_PIN);
  servo1.write(0); servo2.write(0); servo3.write(0);
  pinMode(MIXER_IN1, OUTPUT);
  pinMode(MIXER_IN2, OUTPUT);
  digitalWrite(MIXER_IN1, LOW);
  digitalWrite(MIXER_IN2, LOW);
  pinMode(FAN_IN3, OUTPUT);
  pinMode(FAN_IN4, OUTPUT);
  digitalWrite(FAN_IN3, HIGH);
  digitalWrite(FAN_IN4, LOW);
  pinMode(RELAY_PIN, OUTPUT);
  digitalWrite(RELAY_PIN, HIGH);
  Serial.println("Booting..."); delay(3000);
  servo1.write(180); delay(3000); servo1.write(0); delay(3000);
  servo2.write(90); delay(5000); servo2.write(0);
  digitalWrite(MIXER_IN1, HIGH); digitalWrite(MIXER_IN2, LOW);
  delay(5000);
  digitalWrite(MIXER_IN1, LOW); digitalWrite(MIXER_IN2, LOW);
  servo3.write(90); delay(5000); servo3.write(0);
 }
 void loop() {
  float temp = dht.readTemperature();
  float hum = dht.readHumidity();
  int gas = analogRead(GAS_SENSOR_PIN);
  int moisture = analogRead(MOQ_SENSOR_PIN);
  Serial.print("Temp: "); Serial.print(temp);
  Serial.print(" C | Hum: "); Serial.print(hum);
  Serial.print(" % | Gas: "); Serial.print(gas);
  Serial.print(" | Moisture: "); Serial.println(moisture);
  delay(3000);
 }

Odour-free smart compost bin for urban flats