Drop-in replacement controller board for the Sunlu S1 filament dryer. Features an STM32C011F4P6 microcontroller, 1.8" ST7735 TFT display, dual NTC temperature sensing, and precise PWM heater control; all optimized to fit in just 16 KB of flash.

• Overview
• Features
• Quick Start
• User Guide
• Hardware
• Technical Specs
• Development
• License

Complete replacement for the stock Sunlu S1 control board, maintaining compatibility with the original heating element, chamber, and power connections. Adds a color TFT display in landscape mode and two-button navigation for precise temperature and time control (30–70°C configurable range, exceeding the stock 35–55°C limit).

The firmware uses integer-only math, dirty-check rendering, and batched SPI transfers to fit in the STM32C011's tiny 16 KB flash with room to spare.

Final build

• 1.8" ST7735 TFT: 160×128 px landscape, 16-bit RGB565 color
• Two-button interface: short-press (select/increment), long-press (toggle/cancel)
• Three screens: Main Status, Set Temperature, Set Time
• Smart rendering: dirty-check updates (only changed fields), instant button response

• Dual NTC thermistors: air temp (displayed) + heater element (safety)
• Proportional PWM control (~488 Hz): ramps heater power based on error from target
• Dual safety cutoffs: absolute (85°C) and dynamic (target + 5°C margin)
• Integer-only lookup: 11-point table with linear interpolation, no floating-point library
• Fan control: full speed during drying and overheat emergency

• ~600 lines: single-loop, no RTOS/filesystem
• ~13 KB flash / ~2 KB RAM: 80% flash usage, 33% RAM usage
• Batched SPI: 128-byte buffer (~100× faster than byte-by-byte)
• Minimal font: 5×7 bitmap, 29 glyphs only
• No soft-float: integer NTC lookup saves ~4 KB

Requires arm-none-eabi-gcc, cmake, and cube-cmake installed.

cd Code
cmake --preset Debug
cmake --build build/Debug --target Codede

Using st-flash:

st-flash write build/Debug/Code.bin 0x08000000

Or use the VS Code task "Build and Flash" if configured.

• Top: Air temperature, Countdown timer (HH:MM)
• Middle: Current state (IDLE/RUN/PAUSE), target temperature setting
• Bottom: Action hints: BTN1=set, BTN2=start/pause/resume, hold BTN2=stop/reset

• Value: Current target in °C
• Controls:
  • Short BTN1: increment (or decrement if toggled)
  • Long BTN1: toggle UP/DOWN mode, hints show current direction
  • Short BTN2: confirm & advance to Set TimeTime
  • Long BTN2: cancel & return to MainMain

• Value: Target drying time in HH:MM format
• Controls: Same as Set Temp (BTN1 for ±, long BTN1 to toggle, BTN2 to confirm/cancel)

1. Press BTN1 on Main Screen → Set Temperature
2. Adjust with BTN1 (short = increment, long = toggle direction, watch hints)
3. Press BTN2 → Set Time
4. Adjust similarly, then press BTN2 → firmware returns to Main and starts drying
5. Monitor progress on Main Screen; press BTN2 to pause/resume
6. Hold BTN2 to stop and reset (returns to IDLE)

See Code/Core/Inc/main.h for full pin configuration.

• MCU: STM32C011F4P6 (Cortex-M0+, 32 MHz, 16 KB flash, 6 KB RAM)
• Display: ST7735 1.8" TFT, 160×128 px, 16-bit RGB565, SPI @ 16 MHz
• PWM: TIM1 (heater) + TIM17 (fan), ~488 Hz, 16-bit resolution
• ADC: 12-bit, dual-channel NTC reading @ 500 ms

• Range: 30–70°C (configurable TMIN/TMAX)
• NTC: 100 K, B=3950, ~1°C resolution
• Button poll: 20 ms (30 ms debounce, 1 s long-press)
• Display refresh: 250 ms idle on Main screen, instant on changes
• Countdown: 1 s ticks

• Input: 24 V DC
• Heater: ≤48 W (PWM-controlled)
• Fan: ≤2 W (PWM-controlled)
• MCU + Display: ≤100 mA @ 3.3 V

├── CMakeLists.txt              # Build config
├── Core/
│   ├── Inc/
│   │   ├── main.h              # Pin definitions, HAL config
│   │   ├── dryer.h             # Public firmware API
│   │   └── ...
│   └── Src/
│       ├── main.c              # Entry point, HAL init
│       ├── dryer.c             # Firmware (600 lines): display driver, UI, control
│       └── ...
├── Drivers/
│   ├── CMSIS/
│   ├── STM32C0xx_HAL_Driver/   # ST HAL
│   └── ...
└── cmake/                       # Toolchain files
olchain files

• Temperature limits: edit TMIN, TMAX, TDEF in Code/Core/Src/dryer.c
• Time limits: edit MMIN, MMAX, MDEF
• Safety margin: change stmp + 5 in Regulate() function
• NTC calibration: update ntc[] lookup table in Code/Core/Src/dryer.c

See BOM.csv for the complete component list and part numbers.

This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.