MCP3008.py

# Copyright (c) 2016 Adafruit Industries
# Author: Tony DiCola
#
# 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
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
import Adafruit_GPIO as GPIO
import Adafruit_GPIO.SPI as SPI


class MCP3008(object):
    """Class to represent an Adafruit MCP3008 analog to digital converter.
    """

    def __init__(self, clk=None, cs=None, miso=None, mosi=None, spi=None, gpio=None):
        """Initialize MAX31855 device with software SPI on the specified CLK,
        CS, and DO pins.  Alternatively can specify hardware SPI by sending an
        Adafruit_GPIO.SPI.SpiDev device in the spi parameter.
        """
        self._spi = None
        # Handle hardware SPI
        if spi is not None:
            self._spi = spi
        elif clk is not None and cs is not None and miso is not None and mosi is not None:
            # Default to platform GPIO if not provided.
            if gpio is None:
                gpio = GPIO.get_platform_gpio()
            self._spi = SPI.BitBang(gpio, clk, mosi, miso, cs)
        else:
            raise ValueError('Must specify either spi for for hardware SPI or clk, cs, miso, and mosi for software SPI!')
        self._spi.set_clock_hz(1000000)
        self._spi.set_mode(0)
        self._spi.set_bit_order(SPI.MSBFIRST)

    def read_adc(self, adc_number):
        """Read the current value of the specified ADC channel (0-7).  The values
        can range from 0 to 1023 (10-bits).
        """
        assert 0 <= adc_number <= 7, 'ADC number must be a value of 0-7!'
        # Build a single channel read command.
        # For example channel zero = 0b11000000
        command = 0b11 << 6                  # Start bit, single channel read
        command |= (adc_number & 0x07) << 3  # Channel number (in 3 bits)
        # Note the bottom 3 bits of command are 0, this is to account for the
        # extra clock to do the conversion, and the low null bit returned at
        # the start of the response.
        resp = self._spi.transfer([command, 0x0, 0x0])
        # Parse out the 10 bits of response data and return it.
        result = (resp[0] & 0x01) << 9
        result |= (resp[1] & 0xFF) << 1
        result |= (resp[2] & 0x80) >> 7
        return result & 0x3FF

    def read_adc_difference(self, differential):
        """Read the difference between two channels.  Differential should be a
        value of:
          - 0: Return channel 0 minus channel 1
          - 1: Return channel 1 minus channel 0
          - 2: Return channel 2 minus channel 3
          - 3: Return channel 3 minus channel 2
          - 4: Return channel 4 minus channel 5
          - 5: Return channel 5 minus channel 4
          - 6: Return channel 6 minus channel 7
          - 7: Return channel 7 minus channel 6
        """
        assert 0 <= differential <= 7, 'Differential number must be a value of 0-7!'
        # Build a difference channel read command.
        command = 0b10 << 6                  # Start bit, differential read
        command |= (differential & 0x07) << 3  # Channel number (in 3 bits)
        # Note the bottom 3 bits of command are 0, this is to account for the
        # extra clock to do the conversion, and the low null bit returned at
        # the start of the response.
        resp = self._spi.transfer([command, 0x0, 0x0])
        # Parse out the 10 bits of response data and return it.
        result = (resp[0] & 0x01) << 9
        result |= (resp[1] & 0xFF) << 1
        result |= (resp[2] & 0x80) >> 7
        return result & 0x3FF