# The MIT License (MIT)
#
# Copyright (c) 2017 Scott Shawcroft for Adafruit Industries
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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# THE SOFTWARE.
"""
`adafruit_thermistor`
===========================================================
A thermistor is a resistor that varies with temperature. This driver takes the
parameters of that resistor and its series resistor to determine the current
temperature. To hook one up, connect an analog input pin to the connection
between the resistor and the thermistor. Be careful to note if the thermistor
is connected on the high side (from analog input up to high logic level/3.3 or
5 volts) or low side (from analog input down to ground). The initializer takes
an optional high_side boolean that defaults to True and indicates if that the
thermistor is connected on the high side vs. low side.
* Author(s): Scott Shawcroft
Implementation Notes
--------------------
**Hardware:**
* Adafruit `10K Precision Epoxy Thermistor - 3950 NTC <https://www.adafruit.com/products/372>`_
(Product ID: 372)
* Adafruit `Circuit Playground Express <https://www.adafruit.com/products/3333>`_
(Product ID: 3333)
**Software and Dependencies:**
* Adafruit CircuitPython firmware: https://github.com/adafruit/circuitpython/releases
**Notes:**
#. Check the datasheet of your thermistor for the values.
"""
import math
import analogio
__version__ = "0.0.0-auto.0"
__repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_Thermistor.git"
[docs]class Thermistor:
"""Thermistor driver"""
def __init__(self, pin, series_resistor, nominal_resistance, nominal_temperature,
b_coefficient, *, high_side=True):
# pylint: disable=too-many-arguments
self.pin = analogio.AnalogIn(pin)
self.series_resistor = series_resistor
self.nominal_resistance = nominal_resistance
self.nominal_temperature = nominal_temperature
self.b_coefficient = b_coefficient
self.high_side = high_side
@property
def temperature(self):
"""The temperature of the thermistor in celsius"""
if self.high_side:
# Thermistor connected from analog input to high logic level.
reading = self.pin.value / 64
reading = (1023 * self.series_resistor) / reading
reading -= self.series_resistor
else:
# Thermistor connected from analog input to ground.
reading = self.series_resistor / (65535.0/self.pin.value - 1.0)
steinhart = reading / self.nominal_resistance # (R/Ro)
steinhart = math.log(steinhart) # ln(R/Ro)
steinhart /= self.b_coefficient # 1/B * ln(R/Ro)
steinhart += 1.0 / (self.nominal_temperature + 273.15) # + (1/To)
steinhart = 1.0 / steinhart # Invert
steinhart -= 273.15 # convert to C
return steinhart