heater: Move Thermistor and Linear to their own files in extras/

Move the Thermistor code to a new thermistor.py module.  Move the
Linear code to a new adc_temperature.py module.  This simplifies the
heater.py code.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

1 files changed, 95 insertions, 0 deletions

diff --git a/klippy/extras/thermistor.py b/klippy/extras/thermistor.py
new file mode 100644
index 00000000..22836379
--- /dev/null
+++ b/klippy/extras/thermistor.py
@@ -0,0 +1,95 @@
+# Temperature measurements with thermistors
+#
+# Copyright (C) 2016-2018  Kevin O'Connor <kevin@koconnor.net>
+#
+# This file may be distributed under the terms of the GNU GPLv3 license.
+import math
+
+KELVIN_TO_CELCIUS = -273.15
+SAMPLE_TIME = 0.001
+SAMPLE_COUNT = 8
+REPORT_TIME = 0.300
+
+# Analog voltage to temperature converter for thermistors
+class Thermistor:
+    def __init__(self, config, params):
+        self.pullup = config.getfloat('pullup_resistor', 4700., above=0.)
+        ppins = config.get_printer().lookup_object('pins')
+        self.mcu_adc = ppins.setup_pin('adc', config.get('sensor_pin'))
+        self.mcu_adc.setup_adc_callback(REPORT_TIME, self.adc_callback)
+        self.temperature_callback = None
+        self.c1 = self.c2 = self.c3 = 0.
+        if 'beta' in params:
+            self.calc_coefficients_beta(params)
+        else:
+            self.calc_coefficients(params)
+    def calc_coefficients(self, params):
+        # Calculate Steinhart-Hart coefficents from temp measurements.
+        # Arrange samples as 3 linear equations and solve for c1, c2, and c3.
+        inv_t1 = 1. / (params['t1'] - KELVIN_TO_CELCIUS)
+        inv_t2 = 1. / (params['t2'] - KELVIN_TO_CELCIUS)
+        inv_t3 = 1. / (params['t3'] - KELVIN_TO_CELCIUS)
+        ln_r1 = math.log(params['r1'])
+        ln_r2 = math.log(params['r2'])
+        ln_r3 = math.log(params['r3'])
+        ln3_r1, ln3_r2, ln3_r3 = ln_r1**3, ln_r2**3, ln_r3**3
+
+        inv_t12, inv_t13 = inv_t1 - inv_t2, inv_t1 - inv_t3
+        ln_r12, ln_r13 = ln_r1 - ln_r2, ln_r1 - ln_r3
+        ln3_r12, ln3_r13 = ln3_r1 - ln3_r2, ln3_r1 - ln3_r3
+
+        self.c3 = ((inv_t12 - inv_t13 * ln_r12 / ln_r13)
+                   / (ln3_r12 - ln3_r13 * ln_r12 / ln_r13))
+        self.c2 = (inv_t12 - self.c3 * ln3_r12) / ln_r12
+        self.c1 = inv_t1 - self.c2 * ln_r1 - self.c3 * ln3_r1
+    def calc_coefficients_beta(self, params):
+        # Calculate equivalent Steinhart-Hart coefficents from beta
+        inv_t1 = 1. / (params['t1'] - KELVIN_TO_CELCIUS)
+        ln_r1 = math.log(params['r1'])
+        self.c3 = 0.
+        self.c2 = 1. / params['beta']
+        self.c1 = inv_t1 - self.c2 * ln_r1
+    def setup_minmax(self, min_temp, max_temp):
+        adc_range = [self.calc_adc(min_temp), self.calc_adc(max_temp)]
+        self.mcu_adc.setup_minmax(SAMPLE_TIME, SAMPLE_COUNT,
+                                  minval=min(adc_range), maxval=max(adc_range))
+    def setup_callback(self, temperature_callback):
+        self.temperature_callback = temperature_callback
+    def get_report_time_delta(self):
+        return REPORT_TIME
+    def adc_callback(self, read_time, read_value):
+        # Calculate temperature from adc
+        adc = max(.00001, min(.99999, read_value))
+        r = self.pullup * adc / (1.0 - adc)
+        ln_r = math.log(r)
+        inv_t = self.c1 + self.c2 * ln_r + self.c3 * ln_r**3
+        temp = 1.0/inv_t + KELVIN_TO_CELCIUS
+        self.temperature_callback(read_time + SAMPLE_COUNT * SAMPLE_TIME, temp)
+    def calc_adc(self, temp):
+        inv_t = 1. / (temp - KELVIN_TO_CELCIUS)
+        if self.c3:
+            # Solve for ln_r using Cardano's formula
+            y = (self.c1 - inv_t) / (2. * self.c3)
+            x = math.sqrt((self.c2 / (3. * self.c3))**3 + y**2)
+            ln_r = math.pow(x - y, 1./3.) - math.pow(x + y, 1./3.)
+        else:
+            ln_r = (inv_t - self.c1) / self.c2
+        r = math.exp(ln_r)
+        return r / (self.pullup + r)
+
+Sensors = {
+    "EPCOS 100K B57560G104F": {
+        't1': 25., 'r1': 100000., 't2': 150., 'r2': 1641.9,
+        't3': 250., 'r3': 226.15 },
+    "ATC Semitec 104GT-2": {
+        't1': 20., 'r1': 126800., 't2': 150., 'r2': 1360.,
+        't3': 300., 'r3': 80.65 },
+    "NTC 100K beta 3950": { 't1': 25., 'r1': 100000., 'beta': 3950. },
+}
+
+def load_config(config):
+    # Register default thermistor types
+    pheater = config.get_printer().lookup_object("heater")
+    for sensor_type, params in Sensors.items():
+        func = (lambda config, params=params: Thermistor(config, params))
+        pheater.add_sensor(sensor_type, func)