How to Add a Filament Runout Sensor to Your 3D Printer

To add a filament runout sensor, first mount the sensor on your 3D printer's filament path, then connect its wires to the printer's control board inputs. Finally, update your printer's firmware settings to enable the sensor and test it to ensure it pauses printing when filament runs out.

Syntax

Adding a filament runout sensor involves three main parts:

• Mounting: Physically attach the sensor where the filament passes through.
• Wiring: Connect the sensor's signal and ground wires to the printer's control board inputs, usually labeled as FIL_RUNOUT or similar.
• Firmware Configuration: Enable and configure the sensor in your printer's firmware (e.g., Marlin) by setting the correct pin and enabling the runout detection feature.

c

/* Example Marlin firmware configuration snippet */
#define FILAMENT_RUNOUT_SENSOR
#define FIL_RUNOUT_PIN 2  // Pin number connected to sensor
#define FILAMENT_RUNOUT_SCRIPT "M600"  // Pause command
#define FILAMENT_RUNOUT_DISTANCE_MM 7  // Distance before runout triggers

Example

This example shows how to enable a filament runout sensor in Marlin firmware and connect it to pin 2. The sensor will pause the print using the M600 command when filament runs out.

c

/* Marlin firmware example configuration */
#define FILAMENT_RUNOUT_SENSOR
#define FIL_RUNOUT_PIN 2
#define FILAMENT_RUNOUT_SCRIPT "M600"
#define FILAMENT_RUNOUT_DISTANCE_MM 7

// In pins configuration file
#define FIL_RUNOUT_PIN 2  // Connect sensor signal wire here

// After wiring, upload firmware and test by triggering the sensor manually.

Output

When filament runs out, the printer pauses and waits for filament replacement before resuming.

Common Pitfalls

Common mistakes when adding a filament runout sensor include:

• Incorrect wiring: Mixing up signal and ground wires can cause the sensor not to work.
• Wrong pin configuration: Setting the wrong pin number in firmware will prevent detection.
• Not enabling the sensor in firmware: The sensor must be enabled and configured properly.
• Ignoring sensor type: Some sensors are mechanical switches, others optical; firmware settings may differ.

Always double-check wiring diagrams and firmware documentation for your specific printer and sensor model.

none

/* Wrong wiring example (signal and ground swapped) */
// This will cause no detection or false triggers

/* Correct wiring example */
// Signal wire to FIL_RUNOUT_PIN
// Ground wire to GND pin

Quick Reference

Step	Description
1. Mount Sensor	Attach sensor where filament passes before extruder.
2. Wire Sensor	Connect signal and ground wires to control board pins.
3. Configure Firmware	Enable sensor and set correct pin in firmware.
4. Test Sensor	Trigger sensor to confirm printer pauses print.
5. Replace Filament	Load new filament and resume printing.

Key Takeaways

Mount the filament runout sensor securely in the filament path for accurate detection.

Connect the sensor wires correctly to the printer's control board pins as per documentation.

Enable and configure the filament runout sensor in your printer's firmware before use.

Test the sensor after installation to ensure it pauses printing when filament runs out.

Use the correct sensor type and firmware settings to avoid false triggers or missed detection.