Module: Fan, Scale value for PWM fan

Scale value for fan input based on fan's `min_power` and `max_power`.
As an example, when fan's min_power is set to `0.2`, requesting 1% of fan should translate to roughly `0.2`
This makes it possible to operate fans such as CPAP which generally need
quite high min_power (between 16-30%) operatable at 1%

This also renamed off_below to min_power

Signed-off-by: Jakub Racek <[email protected]>

config/printer-artillery-sidewinder-x2-2022.cfg

@@ -76,15 +76,15 @@ max_temp: 130
 
 [fan]
 pin: PC8
-off_below: 0.1
+min_power: 0.1
 
 [heater_fan extruder]
 pin: PC7
-off_below: 0.2
+min_power: 0.2
 
 [controller_fan case]
 pin: PC6
-off_below: 0.3
+min_power: 0.3
 idle_speed: 0.0
 
 [temperature_sensor mainboard]

config/printer-geeetech-301-2019.cfg

@@ -127,7 +127,7 @@ heaters: extruder
 pin: multi_pin:extruder_fans
 heater: extruder
 max_power: 0.8
-off_below: 0.2
+min_power: 0.2
 shutdown_speed: 0
 
 [mcu]

config/printer-monoprice-select-mini-v2-2018.cfg

@@ -128,7 +128,7 @@ pin: PB8
 # chassis fan
 [controller_fan chassis_fan]
 pin: PB3
-off_below: 0.25
+min_power: 0.25
 
 [mcu]
 serial: /dev/ttyACM0

docs/Config_Changes.md

@@ -8,6 +8,20 @@ All dates in this document are approximate.
 
 ## Changes
 
+20230801: The setting `fan.off_bellow` has been changed to `fan.min_power`.
+However, this change will not affect users who do not utilize this setting.
+With this update, a PWM scaling has been introduced between `min_power` and
+`max_power`. Fans that require a higher `min_power` will now have access to
+their full "safe" power curve. By properly setting `min_power`, any fan
+(such as CPAP) should engage even at `M106 S1`. It's recommended to review
+your slicer/macros to adjust your fan speeds. Your previously designated 20%
+fan speed may no longer represent your lowest fan setting but will now
+correspond to an actual 20% fan speed.
+If you had previously set `max_power` to anything below 1.0 (default),
+it is advisable to recalibrate `min_power` and `kick_start_time` again, with
+the settings `min_power: 0` and `max_power: 1`.
+
+
 20230729: The exported status for `dual_carriage` is changed. Instead of
 exporting `mode` and `active_carriage`, the individual modes for each
 carriage are exported as `printer.dual_carriage.carriage_0` and

docs/Config_Reference.md

@@ -2565,15 +2565,14 @@ Print cooling fan.
 pin:
 #   Output pin controlling the fan. This parameter must be provided.
 #max_power: 1.0
-#   The maximum power (expressed as a value from 0.0 to 1.0) that the
-#   pin may be set to. The value 1.0 allows the pin to be set fully
-#   enabled for extended periods, while a value of 0.5 would allow the
-#   pin to be enabled for no more than half the time. This setting may
-#   be used to limit the total power output (over extended periods) to
-#   the fan. If this value is less than 1.0 then fan speed requests
-#   will be scaled between zero and max_power (for example, if
-#   max_power is .9 and a fan speed of 80% is requested then the fan
-#   power will be set to 72%). The default is 1.0.
+#   The maximum power (0.0 to 1.0) that the pin may be set to. A value
+#   of 1.0 enables the pin fully for extended periods, while 0.5 allows
+#   it for no more than half the time. Use it to limit total power output
+#   (over extended periods) to the fan. This value is combined with
+#   min_power to scale fan speed. With `min_power` at 0.3 and
+#   `max_power` at 1.0, fan speed request scales between 0.3 (min_power)
+#   and 1.0 (max_power). Requesting 10% fan speed results in a value of
+#   0.37. Default is 1.0.
 #shutdown_speed: 0
 #   The desired fan speed (expressed as a value from 0.0 to 1.0) if
 #   the micro-controller software enters an error state. The default
@@ -2593,18 +2592,14 @@ pin:
 #   Time (in seconds) to run the fan at full speed when either first
 #   enabling or increasing it by more than 50% (helps get the fan
 #   spinning). The default is 0.100 seconds.
-#off_below: 0.0
-#   The minimum input speed which will power the fan (expressed as a
-#   value from 0.0 to 1.0). When a speed lower than off_below is
-#   requested the fan will instead be turned off. This setting may be
-#   used to prevent fan stalls and to ensure kick starts are
-#   effective. The default is 0.0.
+#min_power: 0.0
+#   The minimum input power which will power the fan (expressed as a
+#   value from 0.0 to 1.0). The default is 0.0.
 #
-#   This setting should be recalibrated whenever max_power is adjusted.
-#   To calibrate this setting, start with off_below set to 0.0 and the
-#   fan spinning. Gradually lower the fan speed to determine the lowest
+#   To calibrate this setting, start with min_power=0 and max_power=1
+#   Gradually lower the fan speed to determine the lowest
 #   input speed which reliably drives the fan without stalls. Set
-#   off_below to the duty cycle corresponding to this value (for
+#   min_power to the duty cycle corresponding to this value (for
 #   example, 12% -> 0.12) or slightly higher.
 #tachometer_pin:
 #   Tachometer input pin for monitoring fan speed. A pullup is generally
@@ -2642,7 +2637,7 @@ a shutdown_speed equal to max_power.
 #cycle_time:
 #hardware_pwm:
 #kick_start_time:
-#off_below:
+#min_power:
 #tachometer_pin:
 #tachometer_ppr:
 #tachometer_poll_interval:
@@ -2679,7 +2674,7 @@ watched component.
 #cycle_time:
 #hardware_pwm:
 #kick_start_time:
-#off_below:
+#min_power:
 #tachometer_pin:
 #tachometer_ppr:
 #tachometer_poll_interval:
@@ -2725,7 +2720,7 @@ information.
 #cycle_time:
 #hardware_pwm:
 #kick_start_time:
-#off_below:
+#min_power:
 #tachometer_pin:
 #tachometer_ppr:
 #tachometer_poll_interval:
@@ -2783,7 +2778,7 @@ with the SET_FAN_SPEED [gcode command](G-Codes.md#fan_generic).
 #cycle_time:
 #hardware_pwm:
 #kick_start_time:
-#off_below:
+#min_power:
 #tachometer_pin:
 #tachometer_ppr:
 #tachometer_poll_interval:

klippy/extras/fan.py

@@ -13,11 +13,17 @@ def __init__(self, config, default_shutdown_speed=0.):
         self.last_fan_value = 0.
         self.last_fan_time = 0.
         # Read config
-        self.max_power = config.getfloat('max_power', 1., above=0., maxval=1.)
         self.kick_start_time = config.getfloat('kick_start_time', 0.1,
                                                minval=0.)
-        self.off_below = config.getfloat('off_below', default=0.,
+        self.min_power = config.getfloat('min_power', default=0.,
                                          minval=0., maxval=1.)
+        self.max_power = config.getfloat('max_power', 1., above=0., maxval=1.)
+        if self.min_power > self.max_power:
+            raise config.error(
+                "min_power=%f can't be larger than max_power=%f"
+                % (self.min_power, self.max_power)
+            )
+
         cycle_time = config.getfloat('cycle_time', 0.010, above=0.)
         hardware_pwm = config.getboolean('hardware_pwm', False)
         shutdown_speed = config.getfloat(
@@ -46,11 +52,15 @@ def __init__(self, config, default_shutdown_speed=0.):
     def get_mcu(self):
         return self.mcu_fan.get_mcu()
     def set_speed(self, print_time, value):
-        if value < self.off_below:
-            value = 0.
-        value = max(0., min(self.max_power, value * self.max_power))
         if value == self.last_fan_value:
             return
+        if value > 0:
+            # Scale value between min_power and max_power
+            pwm_value =\
+                value * (self.max_power - self.min_power) + self.min_power
+            pwm_value = max(self.min_power, min(self.max_power, pwm_value))
+        else:
+            pwm_value = 0
         print_time = max(self.last_fan_time + FAN_MIN_TIME, print_time)
         if self.enable_pin:
             if value > 0 and self.last_fan_value == 0:
@@ -62,7 +72,7 @@ def set_speed(self, print_time, value):
             # Run fan at full speed for specified kick_start_time
             self.mcu_fan.set_pwm(print_time, self.max_power)
             print_time += self.kick_start_time
-        self.mcu_fan.set_pwm(print_time, value)
+        self.mcu_fan.set_pwm(print_time, pwm_value)
         self.last_fan_time = print_time
         self.last_fan_value = value
     def set_speed_from_command(self, value):