Feature: Fan Control¶

Concept¶

Automatic, hysteresis-based control for cooling fans fitted to the MMU unit itself - motors and electronics, not the printer's part-cooling fan. Each fan is paired with a temperature sensor; MMU_FAN polls the sensor on an interval and switches the fan on above a threshold, off below a lower one, so it isn't chattering on and off right at the boundary.

This feature requires Feature: Environment Manager's sensor to also be enabled - Fan Control reuses the same humidity/temperature sensor(s), and its config block simply doesn't exist in the generated mmu_macro_vars.cfg unless both are switched on together. If you only want a fan running off a fixed schedule or manual control, FAN_FORCED= (below) covers that without needing a sensor at all - but the feature itself still can't be configured without one enabled.

Two hardware layouts, matching Environment Manager's own split:

• Single fan / shared sensor - one fan for the whole enclosure, paired with the one shared environment sensor. The common case.
• Per-gate fans - one fan per gate, on hardware with a per-gate MCU, paired with that gate's own sensor.

Hardware Setup¶

Enabled under MMU Features / Additions → Has cooling fans?, alongside Has environment sensor(s)? from Environment Manager.

A per-gate MCU design shows a Fan pins submenu instead, one pin prompt per gate - blank for any gate without a fan fitted.

Produces, in mmu_hardware.cfg:

[fan_generic _mmu_fan]
pin             : PB5
max_power       : 1.0
kick_start_time : 0.5

or, per-gate:

[fan_generic _unit0_fan0]
pin             : PB5
max_power       : 1.0
kick_start_time : 0.5

(one [fan_generic _<unit>_fan<N>] section per gate with a pin configured).

Parameter Setup¶

Software tuning lives in mmu_macro_vars.cfg's _MMU_FAN_VARS block:

variable_fan_on_temp      : 49.0    # °C - turn fans on above this
variable_fan_off_temp     : 47.0    # °C - turn fans off below this
variable_fan_polling_time : 5.0     # Seconds between temperature checks
variable_fan_control_enabled : True # Automatic control on/off
variable_fan_forced       : 2       # 0=all OFF, 1=all ON, 2=AUTO (per-sensor hysteresis)
variable_fan_sensors      : "unit0_Env"  # Comma-separated temperature_sensor names
variable_fans             : ""           # Comma-separated fan_generic names

fan_on_temp is deliberately higher than fan_off_temp - that gap is the hysteresis band, so a temperature sitting right at the boundary doesn't flip the fan on and off repeatedly.

fan_sensors/fans are meant to be paired lists, index for index - the first sensor drives the first fan, and so on. In practice, check both by hand against what actually got generated:

• Single fan/sensor: fan_sensors correctly picks up your environment sensor's name (e.g. unit0_Env), but fans was found to render blank - set it to match the fan section from Hardware Setup above, e.g. variable_fans: "_mmu_fan".
• Per-gate: neither list gets populated automatically - set both by hand, e.g. variable_fan_sensors: "unit0_Env0, unit0_Env1" and variable_fans: "_unit0_fan0, _unit0_fan1", matching whichever gates actually have both a sensor and a fan fitted.

Commands¶

MMU_FAN                          # Status report
MMU_FAN ENABLE=1                 # Turn on automatic monitoring
MMU_FAN ENABLE=0                 # Turn off monitoring and all fans
MMU_FAN FAN_FORCED=1             # Force every fan on, bypassing sensors
MMU_FAN FAN_FORCED=0             # Force every fan off, bypassing sensors
MMU_FAN FAN_FORCED=2             # Back to automatic per-sensor control

A bare call with no arguments reports current status:

MMU_FAN

Status           : Enabled
Fan polling freq : 5secs
Fan on temp      : 49°C
Fan off temp     : 47°C
Fan forced       : AUTO

Troubleshooting¶

• A fan never turns on - confirm fan_sensors/fans in _MMU_FAN_VARS actually name real, existing temperature_sensor/ fan_generic sections (see the warning above - these are not reliably auto-populated by the installer). Also confirm ENABLE=1 and that FAN_FORCED is 2 (AUTO), not left at 0.
• A fan runs constantly, or never settles - check fan_on_temp is genuinely above fan_off_temp; if they're equal or inverted the hysteresis band collapses and the fan chatters at the boundary.

See also¶

• Feature: Environment Manager - the sensor this feature requires
• Macro Variables: Fan control - every _MMU_FAN_VARS setting in full