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71 lines
1.6 KiB
Python
71 lines
1.6 KiB
Python
"""
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This module reads temperature from NTC thermistor connected to ads111x.
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Circuit diagram for this module should be like this:
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Vcc
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---
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.-.
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'-'
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o----------------o------------> ads111x input
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.-./ |
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|/| R0 NTC ----- 10 uF
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/-' -----
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/ | |
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_|_ _|_
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GND GND
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Since ads111x uses internal reference voltage, Vcc should be well regulated.
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"""
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from __future__ import division
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import math
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import time
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import ads111x as adc
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CELSIUS_TO_KELVIN = 273.15
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# Circuit parameters, resistance in Ohms, temperature in Celsius.
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# Beta is thermistor parameter:
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# https://en.wikipedia.org/wiki/Thermistor#B_or_.CE.B2_parameter_equation
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Vcc = 3.3
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R0 = 100000
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T0 = 25
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BETA = 4092
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R1 = 4700
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Rinf = R0 * math.exp(-BETA / (T0 + CELSIUS_TO_KELVIN))
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def get_temperature(channel):
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"""
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Measure temperature on specified channel.
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:param channel: ads111x channel.
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:return: temperature in Celsius
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"""
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v = adc.measure(channel)
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if v >= Vcc:
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raise IOError("Thermistor not connected")
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if v <= 0:
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raise IOError("Short circuit")
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r = v * R1 / (Vcc - v)
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return (BETA / math.log(r / Rinf)) - CELSIUS_TO_KELVIN
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# for test purpose
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if __name__ == "__main__":
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while True:
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for i in range(0, 4):
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print("T{}={}".format(i, get_temperature(i)))
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print("-----------------------------")
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time.sleep(0.5)
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