temperature_fan: Add support for temperature-triggered fan.

Signed-off-by: Michael Barbour <barbour.michael.0@gmail.com>

klippy/extras/temperature_fan.py

@@ -0,0 +1,44 @@
+# Support fans that are enabled when temperature exceeds a set threshold
+#
+# Copyright (C) 2016-2018  Kevin O'Connor <kevin@koconnor.net>
+#
+# This file may be distributed under the terms of the GNU GPLv3 license.
+import fan
+
+PIN_MIN_TIME = 0.100
+KELVIN_TO_CELCIUS = -273.15
+
+class TemperatureFan:
+    def __init__(self, config):
+        self.name = config.get_name()
+        self.printer = config.get_printer()
+        self.fan = fan.PrinterFan(config)
+        self.mcu = self.fan.mcu_fan.get_mcu()
+        self.fan_speed = config.getfloat('fan_speed', 1., minval=0., maxval=1.)
+        min_temp = config.getfloat('min_temp', minval=KELVIN_TO_CELCIUS)
+        max_temp = config.getfloat('max_temp', above=min_temp)
+        self.temp = config.getfloat('temp', 40. if max_temp > 40. else max_temp,
+            minval=min_temp, maxval=max_temp)
+        self.fan.set_shutdown_speed(1.)
+        self.last_temp = KELVIN_TO_CELCIUS
+        self.sensor = self.printer.lookup_object('heater').setup_sensor(config)
+        self.sensor.setup_minmax(min_temp, max_temp)
+        self.sensor.setup_callback(self.temperature_callback)
+    def printer_state(self, state):
+        if state == 'ready':
+            reactor = self.printer.get_reactor()
+            reactor.register_timer(self.callback, reactor.NOW)
+    def callback(self, eventtime):
+        power = 0.
+        if self.last_temp > self.temp:
+            power = self.fan_speed
+        print_time = self.mcu.estimated_print_time(eventtime) + PIN_MIN_TIME
+        self.fan.set_speed(print_time, power)
+        return eventtime + 1.
+    def temperature_callback(self, read_time, temp):
+        self.last_temp = temp
+    def stats(self, eventtime):
+        return True, '%s: temp=%.1f' % (self.name, self.last_temp)
+
+def load_config_prefix(config):
+    return TemperatureFan(config)