# SPDX-FileCopyrightText: 2018 Carter Nelson for Adafruit Industries
#
# SPDX-License-Identifier: MIT
"""
`ads1x15`
====================================================
CircuitPython base class driver for ADS1015/1115 ADCs.
* Author(s): Carter Nelson
"""
__version__ = "0.0.0+auto.0"
__repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_ADS1x15.git"
import time
from adafruit_bus_device.i2c_device import I2CDevice
from micropython import const
try:
from typing import Dict, List, Optional
from busio import I2C
from microcontroller import Pin
except ImportError:
# define Pin to avoid the error:
# def read(self, pin: Pin, is_differential: bool = False) -> int:
# NameError: name 'Pin' is not defined
Pin = None
_ADS1X15_DEFAULT_ADDRESS = const(0x48)
_ADS1X15_POINTER_CONVERSION = const(0x00)
_ADS1X15_POINTER_CONFIG = const(0x01)
_ADS1X15_CONFIG_OS_SINGLE = const(0x8000)
_ADS1X15_CONFIG_MUX_OFFSET = const(12)
_ADS1X15_CONFIG_COMP_QUE_DISABLE = const(0x0003)
_ADS1X15_CONFIG_GAIN = {
2 / 3: 0x0000,
1: 0x0200,
2: 0x0400,
4: 0x0600,
8: 0x0800,
16: 0x0A00,
}
[docs]
class Mode:
"""An enum-like class representing possible ADC operating modes."""
# See datasheet "Operating Modes" section
# values here are masks for setting MODE bit in Config Register
# pylint: disable=too-few-public-methods
CONTINUOUS = 0x0000
"""Continuous Mode"""
SINGLE = 0x0100
"""Single-Shot Mode"""
[docs]
class ADS1x15:
"""Base functionality for ADS1x15 analog to digital converters.
:param ~busio.I2C i2c: The I2C bus the device is connected to.
:param float gain: The ADC gain.
:param int data_rate: The data rate for ADC conversion in samples per second.
Default value depends on the device.
:param Mode mode: The conversion mode, defaults to `Mode.SINGLE`.
:param int address: The I2C address of the device.
"""
def __init__(
self,
i2c: I2C,
gain: float = 1,
data_rate: Optional[int] = None,
mode: int = Mode.SINGLE,
address: int = _ADS1X15_DEFAULT_ADDRESS,
):
# pylint: disable=too-many-arguments
self._last_pin_read = None
self.buf = bytearray(3)
self.gain = gain
self.data_rate = self._data_rate_default() if data_rate is None else data_rate
self.mode = mode
self.i2c_device = I2CDevice(i2c, address)
@property
def bits(self) -> int:
"""The ADC bit resolution."""
raise NotImplementedError("Subclass must implement bits property.")
@property
def data_rate(self) -> int:
"""The data rate for ADC conversion in samples per second."""
return self._data_rate
@data_rate.setter
def data_rate(self, rate: int) -> None:
possible_rates = self.rates
if rate not in possible_rates:
raise ValueError("Data rate must be one of: {}".format(possible_rates))
self._data_rate = rate
@property
def rates(self) -> List[int]:
"""Possible data rate settings."""
raise NotImplementedError("Subclass must implement rates property.")
@property
def rate_config(self) -> Dict[int, int]:
"""Rate configuration masks."""
raise NotImplementedError("Subclass must implement rate_config property.")
@property
def gain(self) -> float:
"""The ADC gain."""
return self._gain
@gain.setter
def gain(self, gain: float) -> None:
possible_gains = self.gains
if gain not in possible_gains:
raise ValueError("Gain must be one of: {}".format(possible_gains))
self._gain = gain
@property
def gains(self) -> List[float]:
"""Possible gain settings."""
g = list(_ADS1X15_CONFIG_GAIN.keys())
g.sort()
return g
@property
def mode(self) -> int:
"""The ADC conversion mode."""
return self._mode
@mode.setter
def mode(self, mode: int) -> None:
if mode not in (Mode.CONTINUOUS, Mode.SINGLE):
raise ValueError("Unsupported mode.")
self._mode = mode
[docs]
def read(self, pin: Pin, is_differential: bool = False) -> int:
"""I2C Interface for ADS1x15-based ADCs reads.
:param ~microcontroller.Pin pin: individual or differential pin.
:param bool is_differential: single-ended or differential read.
"""
pin = pin if is_differential else pin + 0x04
return self._read(pin)
def _data_rate_default(self) -> int:
"""Retrieve the default data rate for this ADC (in samples per second).
Should be implemented by subclasses.
"""
raise NotImplementedError("Subclasses must implement _data_rate_default!")
def _conversion_value(self, raw_adc: int) -> int:
"""Subclasses should override this function that takes the 16 raw ADC
values of a conversion result and returns a signed integer value.
"""
raise NotImplementedError("Subclass must implement _conversion_value function!")
def _read(self, pin: Pin) -> int:
"""Perform an ADC read. Returns the signed integer result of the read."""
# Immediately return conversion register result if in CONTINUOUS mode
# and pin has not changed
if self.mode == Mode.CONTINUOUS and self._last_pin_read == pin:
return self._conversion_value(self.get_last_result(True))
# Assign last pin read if in SINGLE mode or first sample in CONTINUOUS mode on this pin
self._last_pin_read = pin
# Configure ADC every time before a conversion in SINGLE mode
# or changing channels in CONTINUOUS mode
if self.mode == Mode.SINGLE:
config = _ADS1X15_CONFIG_OS_SINGLE
else:
config = 0
config |= (pin & 0x07) << _ADS1X15_CONFIG_MUX_OFFSET
config |= _ADS1X15_CONFIG_GAIN[self.gain]
config |= self.mode
config |= self.rate_config[self.data_rate]
config |= _ADS1X15_CONFIG_COMP_QUE_DISABLE
self._write_register(_ADS1X15_POINTER_CONFIG, config)
# Wait for conversion to complete
# ADS1x1x devices settle within a single conversion cycle
if self.mode == Mode.SINGLE:
# Continuously poll conversion complete status bit
while not self._conversion_complete():
pass
else:
# Can't poll registers in CONTINUOUS mode
# Wait expected time for two conversions to complete
time.sleep(2 / self.data_rate)
return self._conversion_value(self.get_last_result(False))
def _conversion_complete(self) -> int:
"""Return status of ADC conversion."""
# OS is bit 15
# OS = 0: Device is currently performing a conversion
# OS = 1: Device is not currently performing a conversion
return self._read_register(_ADS1X15_POINTER_CONFIG) & 0x8000
[docs]
def get_last_result(self, fast: bool = False) -> int:
"""Read the last conversion result when in continuous conversion mode.
Will return a signed integer value. If fast is True, the register
pointer is not updated as part of the read. This reduces I2C traffic
and increases possible read rate.
"""
return self._read_register(_ADS1X15_POINTER_CONVERSION, fast)
def _write_register(self, reg: int, value: int):
"""Write 16 bit value to register."""
self.buf[0] = reg
self.buf[1] = (value >> 8) & 0xFF
self.buf[2] = value & 0xFF
with self.i2c_device as i2c:
i2c.write(self.buf)
def _read_register(self, reg: int, fast: bool = False) -> int:
"""Read 16 bit register value. If fast is True, the pointer register
is not updated.
"""
with self.i2c_device as i2c:
if fast:
i2c.readinto(self.buf, end=2)
else:
i2c.write_then_readinto(bytearray([reg]), self.buf, in_end=2)
return self.buf[0] << 8 | self.buf[1]