Smart Coffee Box

An Arduino-based smart storage box for coffee beans and tea leaves.
It monitors temperature, humidity and TVOC, and automatically controls a fan, OLED display and buzzer to protect flavour during storage.

Hardware prototype built with an Arduino MKR WAN 1310, DHT22, SGP30, limit switch, 40×40 mm fan, 0.96" OLED and a piezo buzzer inside a 3D-printed PLA enclosure.

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Features

• Environmental monitoring

  • DHT22 for temperature and relative humidity inside the box
  • SGP30 for TVOC, the total volatile organic compounds in the air
  • Limit switch to detect whether the lid is closed

• Automatic fan control

  • Turns on when humidity or temperature are too high
  • Uses hysteresis so the fan does not flicker on and off all the time
  • Runs in duty cycles, for example 60 seconds on and 180 seconds off, to balance drying and aroma preservation
  • Only runs when the lid is closed

• User feedback

  • 0.96" I²C OLED shows
    • Temperature in °C and humidity in %RH
    • TVOC in ppb
    • Fan status, on or off
    • A simple three-level freshness indicator based on TVOC
    • A blinking warning message when the box is too dry

• Lid-open warning

  • If the lid is left open for more than 60 seconds, a piezo buzzer starts a periodic beep pattern to remind the user to close the box

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Hardware

Microcontroller

• Arduino MKR WAN 1310

Sensors

• DHT22 for temperature and humidity
• SGP30 for TVOC
• Limit switch for lid open or closed detection

Actuators and user interface

• 40×40 mm DC fan driven by an IRLZ44N MOSFET and a 1N4001 flyback diode
• 0.96" I²C OLED display based on an SSD1306 controller, 128×64 pixels
• PKM22EPP-40 piezo buzzer driven from an IO pin through a series resistor of about 100 Ω

Enclosure

• 3D-printed PLA box
• Dedicated desiccant compartment on or near the lid
• Cut-out for the fan and an air flow path across the desiccant
• Mounting points for sensors and the limit switch

More details about wiring and mechanical design can live in:

• hardware/wiring.md
• hardware/enclosure-notes.md

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Wiring – summary

MKR WAN 1310 to modules

• DHT22

  • VCC → 3V3
  • GND → GND
  • DATA → D2

• Limit switch

  • One side → GND
  • Other side → D3, configured as INPUT_PULLUP

• SGP30 over I²C

  • VCC → 3V3
  • GND → GND
  • SDA → A4, SDA line
  • SCL → A5, SCL line

• 0.96" OLED, SSD1306 over I²C

  • VCC → 3V3
  • GND → GND
  • SDA → A4, shared with SGP30
  • SCL → A5, shared with SGP30

• Fan with MOSFET driver

  • Fan positive → 5V
  • Fan negative → MOSFET drain, the middle pin of the IRLZ44N
  • MOSFET source → GND
  • MOSFET gate → D5 through a resistor of about 220 Ω
  • 1N4001 diode for flyback
    • Diode band side → fan positive, 5V
    • Other side → fan negative and MOSFET drain

• Buzzer, PKM22EPP-40

  • Buzzer positive → D6 through a resistor of about 100 Ω
  • Buzzer negative → GND

All grounds must be common, including MKR ground, fan ground, sensors and buzzer.

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Firmware

The main Arduino sketch lives in:

SmartCoffeeBox.ino