218 lines
7.4 KiB
Python
218 lines
7.4 KiB
Python
# The MIT License (MIT)
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#
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# Copyright (c) 2018 Carter Nelson for Adafruit Industries
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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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"""
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`ads1x15`
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====================================================
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CircuitPython base class driver for ADS1015/1115 ADCs.
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* Author(s): Carter Nelson
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"""
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__version__ = "0.0.0-auto.0"
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__repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_ADS1x15.git"
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import time
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from micropython import const
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from adafruit_bus_device.i2c_device import I2CDevice
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# pylint: disable=bad-whitespace
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_ADS1X15_DEFAULT_ADDRESS = const(0x48)
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_ADS1X15_POINTER_CONVERSION = const(0x00)
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_ADS1X15_POINTER_CONFIG = const(0x01)
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_ADS1X15_CONFIG_OS_SINGLE = const(0x8000)
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_ADS1X15_CONFIG_MUX_OFFSET = const(12)
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_ADS1X15_CONFIG_COMP_QUE_DISABLE = const(0x0003)
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_ADS1X15_CONFIG_GAIN = {
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2 / 3: 0x0000,
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1: 0x0200,
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2: 0x0400,
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4: 0x0600,
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8: 0x0800,
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16: 0x0A00,
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}
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# pylint: enable=bad-whitespace
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class Mode:
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"""An enum-like class representing possible ADC operating modes."""
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# See datasheet "Operating Modes" section
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# values here are masks for setting MODE bit in Config Register
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# pylint: disable=too-few-public-methods
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CONTINUOUS = 0x0000
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SINGLE = 0x0100
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class ADS1x15:
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"""Base functionality for ADS1x15 analog to digital converters."""
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def __init__(
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self,
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i2c,
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gain=1,
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data_rate=None,
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mode=Mode.SINGLE,
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address=_ADS1X15_DEFAULT_ADDRESS,
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):
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# pylint: disable=too-many-arguments
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self._last_pin_read = None
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self.buf = bytearray(3)
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self._data_rate = self._gain = self._mode = None
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self.gain = gain
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self.data_rate = self._data_rate_default() if data_rate is None else data_rate
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self.mode = mode
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self.i2c_device = I2CDevice(i2c, address)
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@property
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def data_rate(self):
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"""The data rate for ADC conversion in samples per second."""
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return self._data_rate
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@data_rate.setter
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def data_rate(self, rate):
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possible_rates = self.rates
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if rate not in possible_rates:
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raise ValueError("Data rate must be one of: {}".format(possible_rates))
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self._data_rate = rate
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@property
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def rates(self):
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"""Possible data rate settings."""
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raise NotImplementedError("Subclass must implement rates property.")
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@property
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def rate_config(self):
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"""Rate configuration masks."""
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raise NotImplementedError("Subclass must implement rate_config property.")
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@property
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def gain(self):
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"""The ADC gain."""
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return self._gain
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@gain.setter
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def gain(self, gain):
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possible_gains = self.gains
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if gain not in possible_gains:
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raise ValueError("Gain must be one of: {}".format(possible_gains))
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self._gain = gain
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@property
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def gains(self):
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"""Possible gain settings."""
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g = list(_ADS1X15_CONFIG_GAIN.keys())
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g.sort()
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return g
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@property
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def mode(self):
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"""The ADC conversion mode."""
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return self._mode
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@mode.setter
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def mode(self, mode):
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if mode not in (Mode.CONTINUOUS, Mode.SINGLE):
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raise ValueError("Unsupported mode.")
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self._mode = mode
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def read(self, pin, is_differential=False):
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"""I2C Interface for ADS1x15-based ADCs reads.
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params:
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:param pin: individual or differential pin.
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:param bool is_differential: single-ended or differential read.
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"""
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pin = pin if is_differential else pin + 0x04
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return self._read(pin)
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def _data_rate_default(self):
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"""Retrieve the default data rate for this ADC (in samples per second).
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Should be implemented by subclasses.
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"""
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raise NotImplementedError("Subclasses must implement _data_rate_default!")
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def _conversion_value(self, raw_adc):
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"""Subclasses should override this function that takes the 16 raw ADC
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values of a conversion result and returns a signed integer value.
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"""
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raise NotImplementedError("Subclass must implement _conversion_value function!")
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def _read(self, pin):
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"""Perform an ADC read. Returns the signed integer result of the read."""
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if self.mode == Mode.CONTINUOUS and self._last_pin_read == pin:
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return self._conversion_value(self.get_last_result(True))
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self._last_pin_read = pin
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if self.mode == Mode.SINGLE:
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config = _ADS1X15_CONFIG_OS_SINGLE
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else:
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config = 0
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config |= (pin & 0x07) << _ADS1X15_CONFIG_MUX_OFFSET
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config |= _ADS1X15_CONFIG_GAIN[self.gain]
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config |= self.mode
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config |= self.rate_config[self.data_rate]
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config |= _ADS1X15_CONFIG_COMP_QUE_DISABLE
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self._write_register(_ADS1X15_POINTER_CONFIG, config)
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if self.mode == Mode.SINGLE:
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# poll conversion complete status bit
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while not self._conversion_complete():
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pass
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else:
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# just sleep (can't poll in continuous)
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time.sleep(2 / self.data_rate)
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return self._conversion_value(self.get_last_result(False))
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def _conversion_complete(self):
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"""Return status of ADC conversion."""
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# OS is bit 15
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# OS = 0: Device is currently performing a conversion
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# OS = 1: Device is not currently performing a conversion
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return self._read_register(_ADS1X15_POINTER_CONFIG) & 0x8000
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def get_last_result(self, fast=False):
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"""Read the last conversion result when in continuous conversion mode.
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Will return a signed integer value. If fast is True, the register
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pointer is not updated as part of the read. This reduces I2C traffic
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and increases possible read rate.
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"""
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return self._read_register(_ADS1X15_POINTER_CONVERSION, fast)
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def _write_register(self, reg, value):
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"""Write 16 bit value to register."""
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self.buf[0] = reg
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self.buf[1] = (value >> 8) & 0xFF
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self.buf[2] = value & 0xFF
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with self.i2c_device as i2c:
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i2c.write(self.buf)
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def _read_register(self, reg, fast=False):
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"""Read 16 bit register value. If fast is True, the pointer register
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is not updated.
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"""
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with self.i2c_device as i2c:
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if fast:
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i2c.readinto(self.buf, end=2)
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else:
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i2c.write_then_readinto(bytearray([reg]), self.buf, in_end=2)
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return self.buf[0] << 8 | self.buf[1]
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