ESP32 · Bluetooth LE · iPhone

Know your filament.
Know its moisture.

Q: Do I need an internet connection or an account?

No. SpoolDry talks to your dryer over Bluetooth LE. There is no account, no server and no cloud.

Q: What happens if my iPhone disconnects during drying?

The ESP32 keeps running the session on its own with all safety limits. When you come back, SpoolDry reconnects and updates history, widgets and the Live Activity.

Q: Which hardware do I need?

An Espressif ESP32-C6-DevKitC-1, a Sensirion SHT40 sensor, a 24 V PTC heater, a San Ace 80 fan, logic-level MOSFETs, a relay, an 85 °C thermostat, a 100 °C thermal cutoff and a Mean Well 24 V adapter. See the full BOM above.

Q: How hot can SpoolDry dry?

Hardware v1 is limited to 70 °C chamber temperature (fan rating). That covers PLA, PETG, ABS, ASA, TPU, PA, PC and fiber-filled grades. PEEK, PEI and PPS need 110–150 °C and a dedicated dryer or vacuum oven.

Q: What counts as a free session?

A session counts when your dryer confirms the start command. Failed attempts, app launches and timer views never count. After 3 sessions, SpoolDry Lifetime unlocks unlimited use.

Q: Is the drying data official?

No. The built-in values are typical starting guidance summarised from manufacturer pages (linked). Always follow your filament's data sheet.

SpoolDry connects your filament dryer to your iPhone using Bluetooth. Watch temperature and humidity live, start drying with engineering-polymer profiles and follow the timer on your Lock Screen. No account. No cloud.

Track 3 Bakes Free $19.99 Lifetime

No subscription. One-time purchase. · Coming to the App Store

Everything your dryer was missing

ESP32 BLE Sync

Direct, paired Bluetooth LE link to the ESP32. Versioned protocol with acknowledged commands: the app always shows the dryer's real state.

Engineering Polymers Data

PLA to PEEK, PA-CF and PPS: typical starting guidance with manufacturer sources, never presented as an official requirement.

Live Activity Timers

Lock Screen and Dynamic Island show filament, target, current temperature, humidity and remaining time, straight from the device.

Zero Cloud Setup

No account, no server, no internet. Everything stays between your iPhone and your dryer.

Temperature & Humidity

Sensirion SHT40 accuracy with live charts.

Smart Drying Profiles

Built-in guidance plus your own brand profiles.

Offline History

Start/end humidity, average temperature, charts and statistics.

Safety Monitoring

Firmware limits, watchdog, fan tach, relay, thermostat and thermal fuse.

Multiple Devices

Name and switch between SpoolDry #1, #2 and more.

Lifetime Access

Pay once. Every future improvement included.

How it works

Build the dryer or flash the firmware to your ESP32-C6.

Pair it with SpoolDry over Bluetooth in seconds.

Pick a filament profile and start drying. Follow it on your Lock Screen.

Build Your SpoolDry

A low-voltage (24 V DC) architecture: all mains voltage stays inside a certified, enclosed power adapter. The chamber is limited to 70 °C by the fan rating; independent hardware protects against software faults.

Espressif ESP32-C6-DevKitC-1-N8

Purpose: Controller: BLE link, sensors, control loop and all firmware safety logic.
Recommended specification: ESP32-C6-WROOM-1 · RISC-V 160 MHz · BLE 5 · Wi-Fi 6 · 8 MB flash · 2× USB-C · 3.3 V logic
Why it is used: Official Espressif board, native BLE 5 with mature NimBLE support, USB-C, 8 MB flash for future dual-slot OTA, sold by major distributors.
Example links: DigiKey · Adafruit · Espressif user guide

Sensirion SHT40 breakout (Adafruit #4885)

Purpose: Measures chamber temperature and relative humidity.
Recommended specification: ±0.2 °C / ±1.8 %RH typ. · −40…125 °C · I²C 0x44 · STEMMA QT
Why it is used: Modern, accurate, CRC-protected digital sensor rated to 125 °C. DHT11/DHT22 are slower and far less accurate; AHT20 has no comparable accuracy at high humidity.
Example links: Adafruit · DigiKey

Insulated PTC air heater 24 V / 100 W

Purpose: Heats the air that the fan blows through the chamber.
Recommended specification: 24 V DC · ~100 W (≈4.2 A) · finned aluminium · insulated housing · self-limiting ≤200 °C surface · ~113×35×26 mm
Why it is used: Low-voltage DC (no mains switching), and PTC ceramic limits its own temperature if airflow fails: a physical safety layer.
Example links: Amazon (Bestol 24V 100W) · VXB · DBK (industrial PTC, alternative)

San Ace 80 9GA0824P4G001 (24 V, tach)

Purpose: Moves air through the PTC heater and around the spools; removes moist air.
Recommended specification: 80×80×25 mm · 24 V · 0.21 A · 67 CFM · pulse sensor (2 p/rev) · −20…+70 °C · 60,000 h at 60 °C
Why it is used: Industrial ball-bearing fan rated to 70 °C with a tachometer, so the firmware detects a stalled fan and shuts the heater off. This rating sets SpoolDry's 70 °C chamber limit.
Example links: Sanyo Denki · Mouser (9GA0824P4 series)

Infineon IRLB8721PBF logic-level N-MOSFET

Purpose: Low-side switches for heater PWM (Q1), fan (Q2) and relay coil (Q3).
Recommended specification: 30 V · 62 A · R_DS(on) 8.7 mΩ @ 4.5 V · TO-220 · with 100 Ω gate resistor + 10 kΩ pull-down each
Why it is used: Fully enhanced from 3.3 V logic, runs cool at 4.2 A without a heatsink. Pull-downs keep every load OFF while the ESP32 boots or resets.
Example links: Adafruit #355 · Mouser · Infineon

Omron G5LE-1A4 DC24 relay (K1)

Purpose: Second, independent heater switch in series with the MOSFET.
Recommended specification: SPST-NO · 24 V coil · 10 A contacts · + 1N4001 flyback diode
Why it is used: If Q1 fails shorted, the relay still cuts the heater. Its coil is fed through the 85 °C thermostat, so overheating opens it without any software.
Example links: DigiKey · Omron datasheet

Cantherm F20A08505ACFA06E thermostat (TS1)

Purpose: Independent hardware over-temperature protection for the chamber.
Recommended specification: 85 °C ±5 K · normally closed · auto-reset · potted · 2 A (coil circuit only)
Why it is used: Opens the relay-coil circuit at 85 °C regardless of firmware state (rated 2 A, so it switches the coil, not the 4 A heater).
Example links: DigiKey · Cantherm F20 series

Cantherm SDF-DF100S thermal cutoff (TCO)

Purpose: Last-resort, non-resettable fuse in the heater current path.
Recommended specification: 100 °C one-shot · 10 A AC/DC · axial · crimp, do not solder close to body
Why it is used: Covers the double fault (shorted MOSFET + welded relay). Mount it on the heater duct; replace it if it ever opens and find the cause.
Example links: DigiKey

Semitec 104GT-2 NTC thermistor + 47 kΩ 1 % resistor

Purpose: Measures heater-outlet temperature for derating and fault detection.
Recommended specification: 100 kΩ @ 25 °C · B 4267 K · glass bead to 300 °C
Why it is used: Detects a stalled fan or stuck heater even if the chamber sensor reads normal.
Example links: Mouser

Mean Well GST220A24-R7B desktop adapter

Purpose: Powers everything from 24 V DC. All mains voltage stays inside this certified adapter.
Recommended specification: 24 V · 9.2 A · 221 W · enclosed, safety-certified, 3-pin IEC inlet · 4-pin DIN output
Why it is used: No user mains wiring. 220 W leaves headroom for PTC inrush (2–3× nominal for seconds) plus fan and electronics.
Example links: Mouser · Newark

Kycon KPJX-PM-4S panel jack (mates with R7B plug)

Purpose: Locking 24 V input on the controller box.
Recommended specification: 4-pin DIN power jack · panel mount · 7.5 A
Why it is used: Rated for the current; avoids underrated barrel jacks.
Example links: DigiKey · Kycon datasheet

ATO blade fuse 7.5 A + Littelfuse inline holder

Purpose: Protects wiring from short circuits.
Recommended specification: Slow-acting automotive blade fuse on +24 V directly after the input jack
Why it is used: Sized above heater inrush but below wire and connector ratings.
Example links: Littelfuse 0FHA0002XP (Amazon) · Keystone 3557-2 PCB holder

Pololu D24V10F5 step-down regulator

Purpose: Feeds the ESP32 board's 5 V pin from 24 V.
Recommended specification: 5.1–36 V in · 5 V 1 A out · 18×13 mm
Why it is used: Efficient switching regulator; a linear regulator would overheat dropping 24 → 5 V.
Example links: Pololu

Small parts

Purpose: Assembly, connectors and passive components.
Recommended specification: Perma-Proto board · Phoenix Contact 1935161 terminal blocks · 3× 100 Ω, 4× 10 kΩ, 1× 47 kΩ 1 % · 2× 1N4001 · STEMMA QT 400 mm cable · 18 AWG silicone wire (heater) · 22 AWG (signals)
Why it is used: Screw terminals and silicone wire tolerate heat and vibration better than breadboards and PVC wire.
Example links: Adafruit Perma-Proto (Pololu) · Phoenix 1935161 (DigiKey) · Adafruit 1N4001 #755 · STEMMA QT 400 mm #5385

Hammond 1591XXDSBK ABS enclosure + insulated dry box

Purpose: Keeps electronics cool and away from the heated chamber.
Recommended specification: 152×82×50 mm controller box outside the hot zone · chamber: rigid, insulated box rated ≥ 90 °C (e.g. PP/ABS with foil-faced insulation), heater duct in aluminium or ASA/PC
Why it is used: Only the sensor, NTC, heater, fan, thermostat and TCO sit inside the chamber. Never print the heater duct in PLA or PETG.
Example links: Hammond 1591XX

Bill of Materials

Component	Selected part	Purpose	Qty	Example links
ESP32	Espressif ESP32-C6-DevKitC-1-N8	Controller: BLE link, sensors, control loop and all firmware safety logic.	1	DigiKey · Adafruit
Temperature/humidity sensor	Sensirion SHT40 breakout (Adafruit #4885)	Measures chamber temperature and relative humidity.	1	Adafruit · DigiKey
PTC heater	Insulated PTC air heater 24 V / 100 W	Heats the air that the fan blows through the chamber.	1	Amazon (Bestol 24V 100W) · VXB
Fan	San Ace 80 9GA0824P4G001 (24 V, tach)	Moves air through the PTC heater and around the spools; removes moist air.	1	Sanyo Denki · Mouser (9GA0824P4 series)
MOSFET	Infineon IRLB8721PBF logic-level N-MOSFET	Low-side switches for heater PWM (Q1), fan (Q2) and relay coil (Q3).	3	Adafruit #355 · Mouser
Safety relay	Omron G5LE-1A4 DC24 relay (K1)	Second, independent heater switch in series with the MOSFET.	1	DigiKey · Omron datasheet
Thermostat 85 °C	Cantherm F20A08505ACFA06E thermostat (TS1)	Independent hardware over-temperature protection for the chamber.	1	DigiKey · Cantherm F20 series
Thermal fuse 100 °C	Cantherm SDF-DF100S thermal cutoff (TCO)	Last-resort, non-resettable fuse in the heater current path.	1	DigiKey
Heater NTC	Semitec 104GT-2 NTC thermistor + 47 kΩ 1 % resistor	Measures heater-outlet temperature for derating and fault detection.	1	Mouser
Power supply	Mean Well GST220A24-R7B desktop adapter	Powers everything from 24 V DC. All mains voltage stays inside this certified adapter.	1	Mouser · Newark
Power connector	Kycon KPJX-PM-4S panel jack (mates with R7B plug)	Locking 24 V input on the controller box.	1	DigiKey · Kycon datasheet
Fuse	ATO blade fuse 7.5 A + Littelfuse inline holder	Protects wiring from short circuits.	1	Littelfuse 0FHA0002XP (Amazon) · Keystone 3557-2 PCB holder
5 V regulator	Pololu D24V10F5 step-down regulator	Feeds the ESP32 board's 5 V pin from 24 V.	1	Pololu
Wires, terminals, passives	Small parts	Assembly, connectors and passive components.	1	Adafruit Perma-Proto (Pololu) · Phoenix 1935161 (DigiKey)
Enclosure	Hammond 1591XXDSBK ABS enclosure + insulated dry box	Keeps electronics cool and away from the heated chamber.	1	Hammond 1591XX

Links are examples verified during research (October 2026); availability changes. Equivalent parts with the same ratings work.

Wiring diagram

ESP32-C6 pin map

GPIO	Function	Component	Dir	Notes
`GPIO23`	I²C SDA	SHT40	I/O	Arduino default SDA on ESP32-C6
`GPIO22`	I²C SCL	SHT40	Out	100 kHz, 25 ms timeout, bus recovery
`GPIO18`	Heater PWM	Q1 gate (100 Ω, 10 kΩ pull-down)	Out	LEDC 1 kHz, 10-bit, soft-start
`GPIO21`	Heater enable	Q3 gate → relay K1 coil	Out	HIGH only while PREHEATING/DRYING
`GPIO19`	Fan enable	Q2 gate (100 Ω, 10 kΩ pull-down)	Out	Forced ON whenever heating
`GPIO20`	Fan tach	San Ace pulse sensor	In	10 kΩ pull-up to 3V3, 2 pulses/rev
`GPIO2`	Heater NTC (ADC1_CH2)	104GT-2 + 47 kΩ to 3V3	In	12 dB attenuation, 8-sample average
`GPIO8`	Status LED	On-board RGB LED	Out	Strapping pin; LED only
`GPIO9`	Local button	On-board BOOT button	In	Short: stop · 3 s: reset fault · 10 s: clear bonds
`5V / GND`	Power	Pololu D24V10F5 output	—	Do not also power from USB while on 24 V without care

ESP32 Setup

1. Required hardware

ESP32-C6-DevKitC-1-N8 · USB-C data cable · SHT40 + STEMMA QT cable
(full dryer: see the Bill of Materials above)

2. Install Arduino IDE or PlatformIO

# Arduino IDE 2.x: https://www.arduino.cc/en/software
# or PlatformIO Core:
python3 -m pip install -U platformio

3. Install ESP32 board support

# Arduino IDE → Settings → Additional boards manager URLs:
https://espressif.github.io/arduino-esp32/package_esp32_index.json
# Boards Manager → install "esp32 by Espressif Systems" ≥ 3.3.12

# arduino-cli
arduino-cli core update-index --additional-urls https://espressif.github.io/arduino-esp32/package_esp32_index.json
arduino-cli core install esp32:esp32

4. Connect USB

# Use the USB-C port labelled "UART" on the DevKitC-1.
# Unplug the 24 V supply while flashing from your computer.

5. Select board

# Arduino IDE: Tools → Board → esp32 → "ESP32C6 Dev Module"
#   Flash Size: 8MB · Partition Scheme: Custom (uses SpoolDry/partitions.csv)
# PlatformIO: board = esp32-c6-devkitc-1 (already in platformio.ini)

6. Select port

# macOS: /dev/cu.usbserial-*  ·  Linux: /dev/ttyUSB0  ·  Windows: COM3
arduino-cli board list

7. Install required libraries

# Library Manager → "NimBLE-Arduino" by h2zero ≥ 2.5.1
arduino-cli lib install "NimBLE-Arduino@2.5.1"
# PlatformIO installs it automatically (lib_deps)

8. Compile firmware

cd esp32
pio run
# or
arduino-cli compile --fqbn esp32:esp32:esp32c6:FlashSize=8M,PartitionScheme=custom SpoolDry

9. Flash firmware

pio run -t upload
# or
arduino-cli upload -p /dev/ttyUSB0 --fqbn esp32:esp32:esp32c6:FlashSize=8M,PartitionScheme=custom SpoolDry

10. Open Serial Monitor

pio device monitor -b 115200
# expected:
SpoolDry firmware 1.0.0 (BLE protocol v1) ready as "SpoolDry-A1B2"
Advertising SpoolDry service 5D0F0001-2B7E-4C8A-9B1E-53504F4F4C44

11. Verify BLE advertising

# Any BLE scanner (e.g. nRF Connect) must show "SpoolDry-XXXX"
# advertising service 5D0F0001-2B7E-4C8A-9B1E-53504F4F4C44

12. Open the SpoolDry iOS app

# SpoolDry → Device → Add Dryer (Bluetooth permission prompt appears)

13. Connect device

# Tap "SpoolDry-XXXX" → accept the iOS pairing request
# New phones can pair within 5 min after power-on
# (or hold BOOT for 10 s to clear bonds and reopen pairing)

Firmware download

Version: 1.0.0 · BLE Protocol v1
Board: Espressif ESP32-C6-DevKitC-1-N8 (8 MB)
Framework: Arduino-ESP32 3.3.x (PlatformIO: pioarduino)
Dependencies: NimBLE-Arduino 2.5.x (h2zero)

Configuration: SpoolDry/src/core/Config.h (pins, limits)
Partitions: SpoolDry/partitions.csv (2× 3 MB OTA slots)
Tests: make -C test/host test (33 safety & protocol tests)
Service UUID: 5D0F0001-2B7E-4C8A-9B1E-53504F4F4C44

Download firmware source (.zip)

Typical drying guidance

Typical starting guidance compiled from official manufacturer pages, not a universal requirement. Always follow your filament's data sheet. SpoolDry hardware v1 reaches 70 °C.

Material	Typical temperature	Typical time	SpoolDry start	Sources
PLA	45–60 °C	4–8 h	50 °C · 6 h · <20% RH	Bambu Lab: 50–60 °C · 8 h (blast oven) Prusa Research: 45 °C · 6 h Fiberlogy: 50 °C · 4 h 3DXTECH: 45 °C · 4 h
PETG	55–70 °C	4–8 h	65 °C · 6 h · <20% RH	Bambu Lab: 60–70 °C · 8 h (blast oven) Prusa Research: 55 °C · 6 h Fiberlogy: 60 °C · 4 h 3DXTECH: 65 °C · 4 h
ABS	60–85 °C	4–8 h	70 °C · 6 h · <20% RH	Bambu Lab: 75–85 °C · 8 h (blast oven) Fiberlogy: 60 °C · 4 h 3DXTECH: 80 °C · 4 h
ASA	65–85 °C	4–8 h	70 °C · 6 h · <20% RH	Bambu Lab: 75–85 °C · 8 h (blast oven) Prusa Research: 80 °C · 4 h Fiberlogy: 80 °C · 4 h 3DXTECH: 80 °C · 4 h
TPU	50–75 °C	4–8 h	60 °C · 6 h · <15% RH	Bambu Lab: 65–75 °C · 8 h (blast oven) Prusa Research: 60 °C · 4–6 h 3DXTECH: 65 °C · 4 h
PA (Nylon)	70–90 °C	4–12 h	70 °C · 12 h · <10% RH	Bambu Lab: 75–85 °C · 8–12 h (blast oven) Fiberlogy: 70 °C · 4 h 3DXTECH: 80 °C · 4 h / 90 °C · 4–6 h
PC	70–90 °C	4–8 h	70 °C · 8 h · <15% RH	Polymaker: 70–80 °C · 6–8 h Bambu Lab: 75–85 °C · 8 h (blast oven) Prusa Research: 85 °C · 5 h 3DXTECH: 120 °C · 4 h+
PVA	55–85 °C	4–12 h	65 °C · 8 h · <15% RH	Raise3D: 80 °C · 8–12 h Bambu Lab: 75–85 °C · 8–12 h (blast oven) 3DXTECH: 65 °C · 4 h
BVOH	50–85 °C	4–12 h	55 °C · 6 h · <15% RH	Fiberlogy: 50 °C · 4 h Bambu Lab: 75–85 °C · 8–12 h (blast oven)
PEEK 110–150 °C	120–150 °C	3–6 h	70 °C · 6 h · <10% RH	3DXTECH: 150 °C · 3 h
PEI / ULTEM 110–150 °C	130–150 °C	4–8 h	70 °C · 6 h · <10% RH	3DXTECH: 150 °C · 4–6 h / 130 °C · 4–6 h Prusa Research: 150 °C · 8 h
PPS 110–150 °C	110–140 °C	4–12 h	70 °C · 6 h · <10% RH	Bambu Lab: 110–140 °C · 8–12 h (blast oven) 3DXTECH: 110 °C · 4 h
PA-CF	70–100 °C	4–12 h	70 °C · 12 h · <10% RH	Bambu Lab: 75–85 °C · 8–12 h (blast oven) Prusa Research: 90 °C · 6 h Fiberlogy: 80 °C · 4 h 3DXTECH: 90 °C · 4 h
PA-GF 110–150 °C	75–100 °C	4–16 h	70 °C · 12 h · <10% RH	Forward AM (BASF): 100 °C · 4–16 h Fiberlogy: 80 °C · 4 h 3DXTECH: 90 °C · 4 h Bambu Lab: 75–85 °C · 8–12 h (blast oven)
PETG-CF	60–70 °C	4–8 h	65 °C · 6 h · <20% RH	Bambu Lab: 60–70 °C · 8 h (blast oven) 3DXTECH: 65 °C · 4 h
PLA-CF	45–60 °C	4–8 h	50 °C · 6 h · <20% RH	Bambu Lab: 50–60 °C · 8 h (blast oven)
PC-CF 110–150 °C	80–120 °C	4–8 h	70 °C · 10 h · <15% RH	Prusa Research: 90 °C · 4 h 3DXTECH: 120 °C · 4 h
ASA-CF	65–85 °C	4–8 h	70 °C · 6 h · <20% RH	3DXTECH: 80 °C · 4 h Bambu Lab: 75–85 °C · 8 h (blast oven)
PPS-CF 110–150 °C	110–140 °C	8–12 h	70 °C · 6 h · <10% RH	Bambu Lab: 110–140 °C · 8–12 h (blast oven)

Safety

SpoolDry hardware is a hobby / prototyping project. It is not certified (no CE, UL or similar). You build and operate it at your own risk.

Never bypass the thermal fuse or the thermostat.
Never operate damaged wiring or connectors.
Use the specified, certified 24 V power supply.
Do not exceed the heater, wire and connector ratings.
Keep flammable materials away from exposed heating elements.
Use a proper, heat-rated enclosure; keep electronics outside the hot zone.
Use independent thermal protection in addition to the firmware.
Do not leave an experimental prototype unattended.

Protection layers

Firmware: 80 °C absolute, target +8 °C/30 s, sensor CRC & plausibility, fan tach, heater-NTC derating, runaway & stuck-heater detection, 5 s watchdog
Heater defaults OFF: 10 kΩ gate pull-downs, outputs driven LOW first at boot, sessions never resume after reset
Two independent switches in the heater path: MOSFET Q1 + relay K1
85 °C bimetal thermostat opens the relay coil without software
100 °C one-shot thermal cutoff in the heater current
Self-limiting PTC element (power collapses without airflow)
7.5 A fuse · certified, enclosed 24 V supply (no user mains wiring)

Simple pricing

Free

3 complete drying sessions with every feature, one dryer.

SpoolDry Lifetime

$19.99

Unlimited sessions, multiple dryers, all future improvements. $19.99 in the US App Store; local prices are shown by the App Store.

No subscription. One-time purchase.

Frequently asked questions

No. SpoolDry talks to your dryer over Bluetooth LE. There is no account, no server and no cloud.

The ESP32 keeps running the session on its own with all safety limits. When you come back, SpoolDry reconnects and updates history, widgets and the Live Activity.

An Espressif ESP32-C6-DevKitC-1, a Sensirion SHT40 sensor, a 24 V PTC heater, a San Ace 80 fan, logic-level MOSFETs, a relay, an 85 °C thermostat, a 100 °C thermal cutoff and a Mean Well 24 V adapter. See the full BOM above.

Hardware v1 is limited to 70 °C chamber temperature (fan rating). That covers PLA, PETG, ABS, ASA, TPU, PA, PC and fiber-filled grades. PEEK, PEI and PPS need 110–150 °C and a dedicated dryer or vacuum oven.

A session counts when your dryer confirms the start command. Failed attempts, app launches and timer views never count. After 3 sessions, SpoolDry Lifetime unlocks unlimited use.

No. The built-in values are typical starting guidance summarised from manufacturer pages (linked). Always follow your filament's data sheet.