Toasty is a DIY, Arduino Nano–based controller that turns a household 220 V AC food dehydrator into a reliable 3D-printer filament dryer. It uses an AHT21 temperature/humidity sensor, a 20×4 I²C LCD, four push buttons, a 5 V active-HIGH relay, and a 5 V buzzer. The firmware includes preset temperature/humidity targets for common filaments and a Hold Mode that prevents re-moisture after the timer ends.

• Deliver a low-cost, beginner-friendly controller for consistent filament drying.
• Keep material within safe temperature while reducing humidity.
• Provide ready-made profiles for popular materials and allow easy tweaks.
• Support continuous drying/storage for up to 3 spools inside a modified dehydrator.

• Reduces stringing, bubbles, and warping by removing moisture.
• Extends the life of engineering filaments.
• Reuses a modified 220 V AC dehydrator as the drying chamber.
• Controller runs on a safe 5 V/2 A DC supply, isolated from mains.
• Hold Mode keeps air moving after the timer to avoid re-wetting.
• Buildable with intermediate → beginner electronics skills.

• 8 material profiles (PLA, PETG/CPE/PCTG, ABS, ASA, TPU, Nylon, PC, PP).
• 20×4 I²C LCD status UI with centered error messages.
• Four buttons (OK / UP / DOWN / CANCEL) with external pull-downs (pressed = HIGH).
• Active-HIGH relay (no beeps on relay changes; buzzer for UI/errors).
• Separate hysteresis for temperature and humidity.
• User-visible timer; when it ends, system enters Hold Mode.

Core: Arduino Nano Sensor: AHT21 (Adafruit AHTX0) @ I²C 0x38 LCD: 20×4 I²C @ 0x27 Power: 5 V/2 A DC (controller) + 220 V AC (dehydrator heater/fan via relay)

Mains note: The relay must switch the 220 V AC line to the dehydrator’s heater/fan. Keep low-voltage and mains wiring well isolated.

• Arduino Nano (or compatible)

• AHT21 sensor module (Adafruit AHTX0 compatible)

• 20×4 I²C LCD @ 0x27

• 4 × momentary push buttons + external pull-down resistors

• 5 V active-HIGH relay module (mains-rated, proper isolation)

• 5 V buzzer

• 5 V/2 A DC power supply (controller board)

• Modified 220 V AC food dehydrator (drying chamber)

• Enclosure, wiring, terminal blocks, heat-shrink, etc.

• 🔧 Modification Instructions:
  Watch the tutorial video by Christopher Lum for guidance on physical modification in the food dehydrator setup.

  🎥 YouTube – Christopher Lum: Turning a Food Dehydrator into a Filament Dryer)

Hysteresis (defaults): tempHys = 1.5 °C, humHys = 3 %RH

Tune inside loadProfile(id) or via the globals near the top of the sketch.

1. Boot & Sensor Check — Initializes AHT21 and LCD. If the sensor is missing, shows a centered ERROR: AHT21 not found, beeps, and locks out with the relay OFF.
2. Home Screen — Shows “Toasty Filament Dryer” and live T/H readings.
3. Profile Menu — Press OK to open the selector (1–8). Navigate with UP/DOWN, OK to start, CANCEL to exit.
4. Run — Control loop maintains setpoints using independent hysteresis for temperature and humidity.
5. Timer — A user-visible countdown runs (it does not hard-stop the run).
6. Hold Mode — When the timer ends, the display shows Done (Hold) and the relay continues as required to prevent re-moisture.
7. Stop Anytime — Press CANCEL to stop; relay turns OFF and the system returns to Home.

• Relay ON when t ≤ setTemp − tempHys AND h ≥ setHum + humHys

• Relay OFF when t ≥ setTemp OR h ≤ setHum

• Otherwise (between bands), the relay holds its last state

Language: Arduino C++ Libraries:

Wire
Adafruit_AHTX0
LiquidCrystal_I2C

1. Install libraries via Arduino Library Manager.
2. Select Arduino Nano (ATmega328P) in the IDE.
3. Open the provided main.ino file.
4. Compile & Upload.

• Edit loadProfile(id) to tune Set Temp, Target RH, and Max Run Time.
• Adjust tempHys / humHys for responsiveness vs. stability.
• UI strings live in showHomeHeader, showRunHeader, etc.
• Error messages are pre-centered for a 20×4 LCD.

• PLA: Default Set Temp = 45 °C. If your unit overshoots, reduce the setpoint or improve airflow.
• Nylon/PC: High temps—confirm your dehydrator/enclosure can handle them safely.
• Multi-spool storage: Keep Hold Mode active between prints to prevent re-wetting.

• AHT21 not found: Check I²C wiring (SDA=A4, SCL=A5), address, power, and module pull-ups.
• Relay always ON/OFF: Verify active-HIGH wiring, pin D7, and thresholds.
• LCD blank/garbled: Confirm I²C address 0x27 and constructor (0x27, 20, 4).
• Buttons inverted: Buttons must use external pull-downs; pressed = HIGH.

• The dehydrator’s heater/fan is 220 V AC. Disconnect power before wiring.
• Enclose all mains parts; insulate and strain-relieve cables.
• Use a relay module rated for your load with proper isolation/clearances.
• Keep low-voltage and mains wiring physically separated.
• If unsure, consult a qualified person.

📁 File Path: Open

📁 File Path: Open

Open issues and send PRs to improve docs, profiles, and wiring notes.

Copyright © 2025 Abhijeet Kumar. Licensed under CC0-1.0 LICENSE

Hardware/firmware by Toasty project. Library credits: Adafruit AHTX0, LiquidCrystal_I2C.