79 lines
3.1 KiB
Python
79 lines
3.1 KiB
Python
# Copyright (c) 2015 Troy Dack
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# Author: Troy Dack
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#
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# Permission is hereby granted, free of charge, to any person obtaining a copy
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# of this software and associated documentation files (the "Software"), to deal
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# in the Software without restriction, including without limitation the rights
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# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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# copies of the Software, and to permit persons to whom the Software is
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# furnished to do so, subject to the following conditions:
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#
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# The above copyright notice and this permission notice shall be included in
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# all copies or substantial portions of the Software.
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#
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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# THE SOFTWARE.
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import logging
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import Adafruit_GPIO as GPIO
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import Adafruit_GPIO.SPI as SPI
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class MAX6675(object):
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"""Class to represent a MAX6675 thermocouple temperature measurement board.
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"""
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def __init__(self, clk=None, cs=None, do=None, spi=None, gpio=None):
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"""Initialize MAX6675 device with software SPI on the specified CLK,
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CS, and DO pins. Alternatively can specify hardware SPI by sending an
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Adafruit_GPIO.SPI.SpiDev device in the spi parameter.
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"""
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self._logger = logging.getLogger('MAX6675.MAX6675')
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self._spi = None
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# Handle hardware SPI
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if spi is not None:
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self._logger.debug('Using hardware SPI')
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self._spi = spi
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elif clk is not None and cs is not None and do is not None:
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self._logger.debug('Using software SPI')
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# Default to platform GPIO if not provided.
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if gpio is None:
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gpio = GPIO.get_platform_gpio()
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self._spi = SPI.BitBang(gpio, clk, None, do, cs)
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else:
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raise ValueError('Must specify either spi for for hardware SPI or clk, cs, and do for softwrare SPI!')
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self._spi.set_clock_hz(5000000)
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self._spi.set_mode(0)
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self._spi.set_bit_order(SPI.MSBFIRST)
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def readTempC(self):
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"""Return the thermocouple temperature value in degrees celsius."""
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v = self._read16()
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# Check for error reading value.
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if v & 0x4:
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return float('NaN')
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# Check if signed bit is set.
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if v & 0x80000000:
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# Negative value, take 2's compliment. Compute this with subtraction
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# because python is a little odd about handling signed/unsigned.
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v >>= 3 # only need the 12 MSB
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v -= 4096
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else:
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# Positive value, just shift the bits to get the value.
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v >>= 3 # only need the 12 MSB
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# Scale by 0.25 degrees C per bit and return value.
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return v * 0.25
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def _read16(self):
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# Read 16 bits from the SPI bus.
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raw = self._spi.read(2)
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if raw is None or len(raw) != 2:
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raise RuntimeError('Did not read expected number of bytes from device!')
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value = raw[0] << 8 | raw[1]
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self._logger.debug('Raw value: 0x{0:08X}'.format(value & 0xFFFFFFFF))
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return value
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