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Ben Lye 189171b6be hall_filament_width_sensor: Toggle for flow compensation

Adds a toggle to enable or disable flow compensation based on the filament
width sensor readings without disabling the sensor entirely.

Useful on printers where the hall effect sensor which is too inaccurate to
helpfully adjust the extrusion multiplier, but is good enough to act as a
filament runout sensor.

Includes commands to enable and disable flow compensation, and to query the
state. Also includes updates to the relevant doc pages.

Signed-off-by: Ben Lye ben@lye.co.nz

2026-02-28 07:38:55 +00:00

3.3 KiB

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Hall filament width sensor

This document describes Filament Width Sensor host module. Hardware used for developing this host module is based on two Hall linear sensors (ss49e for example). Sensors in the body are located on opposite sides. Principle of operation: two hall sensors work in differential mode, temperature drift same for sensor. Special temperature compensation not needed.

You can find designs at Thingiverse, an assembly video is also available on Youtube

To use Hall filament width sensor, read Config Reference and G-Code documentation.

How does it work?

Sensor generates two analog output based on calculated filament width. Sum of output voltage always equals to detected filament width. Host module monitors voltage changes and adjusts extrusion multiplier. I use the aux2 connector on a ramps-like board with the analog11 and analog12 pins. You can use different pins and different boards.

[menu __main __filament __width_current]
type: command
enable: {'hall_filament_width_sensor' in printer}
name: Dia: {'%.2F' % printer.hall_filament_width_sensor.Diameter}
index: 0

[menu __main __filament __raw_width_current]
type: command
enable: {'hall_filament_width_sensor' in printer}
name: Raw: {'%4.0F' % printer.hall_filament_width_sensor.Raw}
index: 1

Calibration procedure

To get raw sensor value you can use menu item or QUERY_RAW_FILAMENT_WIDTH command in terminal.

Insert first calibration rod (1.5 mm size) get first raw sensor value
Insert second calibration rod (2.0 mm size) get second raw sensor value
Save raw sensor values in config parameter Raw_dia1 and Raw_dia2

How to enable sensor

By default, the sensor is disabled at power-on.

To enable the sensor, issue ENABLE_FILAMENT_WIDTH_SENSOR command or set the enable parameter to true.

Use as a runout switch only

By default, the sensor measures filament diameter and adjusts extrusion multiplier to compensate for variations.

If you want to use the sensor as a runout switch only, set the enable_flow_compensation config parameter to false. In this mode, the sensor will only trigger runout events when filament is not detected, it will not modify the extrusion multiplier.

This is useful for printers where the filament sensor is not accurate enough for flow compensation but can reliably detect filament runout, or when printing with flexible filaments which have unstable diameter characteristics.

Issue ENABLE_FILAMENT_WIDTH_COMPENSATION to enable flow compensation or DISABLE_FILAMENT_WIDTH_COMPENSATION to disable it.

Note that disabling filament width compensation automatically resets the extrusion multiplier to 100%.

QUERY_FILAMENT_WIDTH_COMPENSATION returns the current state of flow compensation.

Logging

By default, diameter logging is disabled at power-on.

Issue ENABLE_FILAMENT_WIDTH_LOG command to start logging and issue DISABLE_FILAMENT_WIDTH_LOG command to stop logging. To enable logging at power-on, set the logging parameter to true.

Filament diameter is logged on every measurement interval (10 mm by default).

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