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Bill of Materials — IWM Reverse Vending Machine

All components are widely available on Amazon India, Robu.in, or local electronics markets (Bangalore: SP Road, Mumbai: Lamington Road). Total build cost for this prototype: ~₹15,000 including enclosure and miscellaneous hardware.

Electronics

# Component Spec / Model Qty Where to buy
1 Microcontroller Arduino Uno R3 (ATmega328P) 1 Amazon / Robu
2 Ultrasonic sensor HC-SR04 2 Amazon / Robu
3 Inductive proximity sensor LJ12A3-4-Z/BX · NPN · NO · 4mm · 6–36V 1 Robu / Amazon
4 Capacitive proximity sensor LJC18A3-H-Z/BX · NPN · NO · 8mm 1 Robu / Amazon
5 Load cell Bar type · 50 kg rated 1 Amazon / Robu
6 Load cell ADC HX711 breakout module 1 Amazon / Robu
7 DC motor 12V · ~300 RPM (geared) 1 Local market
8 Motor driver L298N dual H-bridge module 1 Amazon / Robu
9 Servo motor SG90 or MG90S (9g micro servo) 1 Amazon / Robu
10 LCD display 16×2 with I2C backpack (PCF8574 · 0x27) 1 Amazon / Robu
11 Thermal printer 58mm serial thermal printer · 9600 baud 1 Amazon
12 Thermal paper roll 58mm × 30m 2–3 Amazon
13 Active buzzer 3–5V · self-oscillating 1 Amazon / Robu
14 Push button Momentary NO · panel mount 1 Local market

Power Supply

# Component Spec Qty Notes
15 DC adapter 12V · 2A · barrel jack 1 Powers motor via L298N
16 DC adapter 5V · 2A · USB or barrel 1 Powers thermal printer
17 USB cable Type-B (Arduino) 1 Powers Arduino from laptop or 5V adapter

Conveyor Belt Assembly

# Component Spec Qty Notes
18 MDF board 6mm · cut to ~50×15 cm 1 Conveyor base platform
19 Rubber conveyor belt Flat · ~50 cm loop 1 Repurposed or cut from rubber sheet
20 Roller rod 6mm dia · aluminium or PVC 2 Drive roller + idler roller
21 Motor mount bracket L-bracket or 3D printed 1 Mounts DC motor to MDF

Enclosure

# Component Qty Notes
22 Coroplast sheet (corrugated plastic) ~4 sq ft White · 4–6mm thick · main enclosure panels
23 Aluminium angle bracket 2 cm × 2 cm × various lengths ~8–10
24 M4 screws + nuts M4 × 10mm ~50
25 Castor wheels 40–50mm with lock 4
26 Hinge + latch Small cabinet hinge + magnetic latch 2 each
27 Snap-in frame A4 or custom poster frame 1

Wiring & Misc

# Component Qty Notes
28 Jumper wires Male-to-male + male-to-female ~40–50
29 Breadboard Full size (830 tie points) 1
30 Dupont crimp connectors Assorted 1 pack
31 Heat shrink tubing Assorted sizes 1 pack
32 Velcro / cable ties — 1 pack

Notes

  • Inductive and capacitive sensors need 6–36V to operate — they share the 12V adapter with the motor driver. Do NOT connect them to Arduino's 5V pin.
  • Thermal printer draws up to 2A during printing — it must have its own dedicated 5V adapter. Running it off the Arduino 5V rail will cause resets.
  • Load cell calibration — once assembled, you'll need to calibrate the HX711 with a known weight (a 20g coin or a 20g object off a kitchen scale works fine) and store the calibration factor in EEPROM. There's no shortcut here; every load cell + HX711 pair is slightly different.
  • Servo — the SG90 is fine for a lightweight trapdoor. If your trapdoor panel is heavier (thick acrylic/MDF), upgrade to MG90S which has metal gears.