SUNLU AMS Heater Auto-Vent Controller - Technical Specification

1. System Overview

The SUNLU AMS Heater Auto-Vent Controller is an intelligent automation system designed for 3D printer filament dryers. It monitors AC current consumption to detect heater and fan operation states, automatically controlling a servo-operated vent to optimize humidity removal and temperature management.

1.1 Key Features

• Automatic Current Monitoring: Real-time AC current sensing with offset compensation
• Intelligent State Detection: Distinguishes between heater-on, fan-only, and idle states
• Self-Learning Calibration: Adapts to different dryer models through automated threshold learning
• Non-Volatile Memory: Stores learned parameters in EEPROM for persistence across power cycles
• Visual Feedback: Multi-pattern LED status indication
• User Interface: Three-mode button control (short/long/very-long press)
• Cooldown Management: 3-minute delay for fan-only operation after heater shutoff

2. Hardware Specifications

2.1 Microcontroller

The controller supports two compatible microcontroller options:

Option 1: Seeed XIAO SAMD21

• Processor: ARM Cortex-M0+ @ 48MHz
• Operating Voltage: 3.3V
• Flash Memory: 256KB
• SRAM: 32KB
• I/O Voltage: 3.3V logic levels

Option 2: Seeed XIAO RP2040

• Processor: Dual ARM Cortex-M0+ @ 133MHz
• Operating Voltage: 3.3V
• Flash Memory: 2MB
• SRAM: 264KB
• I/O Voltage: 3.3V logic levels

Both microcontrollers use the same pinout and are pin-compatible for this application.

2.2 Current Sensor

• Model: ACS758 LCB-050B
• Type: Hall-effect AC/DC current sensor
• Measurement Range: ±50A
• Sensitivity: 40mV/A @ 5V supply
• Output Type: Analog voltage (ratiometric)
• Bandwidth: DC to 100kHz

2.3 Analog-to-Digital Converter (ADS1115)

• Model: ADS1115
• Resolution: 16-bit
• Interface: I2C (address 0x48)
• Input Range: ±4.096V (GAIN_ONE configuration)
• LSB Size: 0.125mV
• Sample Rate: Configurable, default 128 SPS
• Channels Used:
  • A0: Current sensor input
  • A1: Servo feedback input

2.4 Servo Motor

• Type: Feedback-enabled servo
• Control: PWM signal (standard servo protocol)
• Position Range: 0° to 180°
• Feedback: Analog voltage proportional to position
• Operating Voltage: 5V (separate power supply recommended)

2.5 User Interface

• LED: Single status indicator

  • Type: Standard LED
  • Configuration: Active low (cathode to GPIO, anode to VCC through resistor)
  • Pin: D10

• Button: Momentary push button

  • Type: SPST normally-open
  • Configuration: Active low with internal pullup resistor
  • Pin: D3

3. Software Architecture

3.1 Operating Modes

3.1.1 Normal Operation Mode

• Continuous current monitoring
• State detection (heater, fan, idle)
• Automatic vent control
• LED status indication (solid when active)

3.1.2 Standby Mode

• System disabled
• LED off
• Vent remains in current position
• Triggered by 2-5 second button press

3.1.3 Learning Mode

• Three-phase automatic calibration
• LED pattern guidance for user
• EEPROM storage of learned thresholds
• Triggered by 5+ second button press

3.2 Current Measurement Algorithm

3.2.1 Offset Compensation

At startup, the system measures the zero-current baseline for 5 seconds:

voltageOffset = average(ADC_readings) over 5 seconds

3.2.2 RMS Calculation

AC current is measured using Welford's online algorithm for numerical stability:

For each sample over 500ms:
    voltage = ADC_reading - voltageOffset
    Update running mean and variance
RMS_voltage = sqrt(variance)
RMS_current = RMS_voltage / sensitivity

3.2.3 Rolling Average

A 30-second rolling average smooths transient variations:

samples[] = circular buffer of 60 samples (0.5s each)
average_current = mean(samples[])

3.3 State Detection

The system uses hysteresis-based thresholds to prevent chattering:

Default thresholds (before learning):

• HEATER_ON_THRESHOLD: 200mA
• HEATER_OFF_THRESHOLD: 120mA
• FAN_ON_THRESHOLD: 25mA
• FAN_OFF_THRESHOLD: 20mA

3.4 Vent Control Logic

IF (heater_detected OR fan_detected):
    OPEN vent

IF (heater_off AND fan_detected):
    Keep vent OPEN
    Start cooldown timer

IF (heater_off AND fan_off AND cooldown_expired):
    CLOSE vent after 3 minutes

IF (heater_off AND fan_off AND NOT in_cooldown):
    CLOSE vent immediately

3.5 Learning Mode Algorithm

Phase 1: Baseline Measurement

1. LED: SOLID (5 second prep time)
2. User ensures dryer is OFF
3. LED: FAST FLASH (10 second measurement)
4. Records: baseline_current = avg(measurements)
5. LED: SUCCESS BLINK

Phase 2: Heater + Fan Measurement

1. LED: BREATHING pattern (5 second prep time)
2. User turns dryer ON (heater + fan)
3. LED: FAST FLASH (10 second measurement)
4. Records: heater_current = max(measurements)
5. LED: SUCCESS BLINK

Phase 3: Fan-Only Measurement

1. LED: DOUBLE BLINK pattern (5 second prep time)
2. User turns heater OFF (fan continues)
3. LED: FAST FLASH (10 second measurement)
4. Records: fan_current = avg(measurements)
5. LED: COMPLETE BLINK (3 long flashes)

Threshold Calculation

FAN_ON_THRESHOLD = (baseline + fan_current) / 2 + 2mA margin
FAN_OFF_THRESHOLD = FAN_ON_THRESHOLD - 5mA hysteresis

HEATER_ON_THRESHOLD = (fan_current + heater_current) / 2
HEATER_OFF_THRESHOLD = (baseline + fan_current) / 2 + 5mA margin

Thresholds are saved to EEPROM with magic number validation.

3.6 EEPROM Storage

struct ThresholdData {
    uint32_t magic;  // 0xABCD1234 for validation
    float fanOnThreshold;
    float fanOffThreshold;
    float heaterOnThreshold;
    float heaterOffThreshold;
};

SAMD21: Uses FlashStorage library for EEPROM emulation in flash memory. RP2040: Uses LittleFS or EEPROM emulation library for persistent storage in flash memory.

3.7 LED Patterns

3.8 Button Interface

4. Timing Specifications

5. Memory Usage

SAMD21:

• Flash: ~57KB / 256KB (22%)
• SRAM: Estimated ~4KB / 32KB (12%)
• EEPROM: 20 bytes (threshold storage)

RP2040:

• Flash: ~57KB / 2MB (<3%)
• SRAM: Estimated ~4KB / 264KB (<2%)
• EEPROM: 20 bytes (threshold storage in flash)

6. Communication Interfaces

6.1 I2C Bus

• Speed: 100kHz (standard mode)
• Device: ADS1115 @ 0x48

6.2 Serial Console (Debug)

• Baud Rate: 115200
• Format: 8N1
• Purpose: Debug output and manual control commands

6.3 Serial Commands (Debug Mode)

7. Power Requirements

• Microcontroller: 3.3V @ ~50mA (active), ~15mA (idle)
• ADS1115: 3.3V @ ~1mA
• Servo: 5V @ 100-500mA (load dependent)
• Total System: 5V @ 200-600mA typical

Recommended: Use separate 5V power supply for servo, common ground with microcontroller.

8. Environmental Specifications

• Operating Temperature: 0°C to 50°C
• Storage Temperature: -20°C to 70°C
• Humidity: 10% to 90% non-condensing
• Altitude: Up to 2000m

9. Safety Features

• Offset Compensation: Eliminates DC bias errors
• Rolling Average: Filters transient spikes
• Hysteresis: Prevents rapid state changes
• Cooldown Delay: Protects dryer fan bearing
• Watchdog: None (consider adding for production)
• Overcurrent Protection: Relies on ACS758 internal protection

10. Calibration Procedure

10.1 Servo Calibration

Performed automatically at startup:

1. Move to closed position (180°)
2. Record feedback voltage
3. Move to open position (0°)
4. Record feedback voltage
5. Create linear mapping between feedback and position

10.2 Current Threshold Learning

See Section 3.5 for detailed algorithm.

11. Error Handling

• ADS1115 Not Found: System halts with error message
• Servo Feedback Out of Range: Warning message, continues operation
• EEPROM Read Invalid: Uses default thresholds

12. Future Enhancements

Potential improvements for future versions:

1. Watchdog Timer: Auto-reset on system hang
2. Temperature Sensing: Direct dryer temperature monitoring
3. WiFi Connectivity: Remote monitoring and control
4. Data Logging: Historical current and state data
5. Adjustable Cooldown: User-configurable delay time
6. Multiple Profiles: Store settings for different dryers
7. OLED Display: On-device status display
8. Emergency Stop: Hardware override for safety