# The MIT License (MIT)
#
# Copyright (c) 2017 Carter Nelson for Adafruit Industries
#
# 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.
"""
`adafruit_ads1x15`
====================================================
CircuitPython 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 micropython import const
from adafruit_bus_device.i2c_device import I2CDevice
# Register and other configuration values:
# pylint: disable=bad-whitespace
ADS1X15_DEFAULT_ADDRESS = const(0x48)
ADS1X15_POINTER_CONVERSION = const(0x00)
ADS1X15_POINTER_CONFIG = const(0x01)
ADS1X15_POINTER_LOW_THRESHOLD = const(0x02)
ADS1X15_POINTER_HIGH_THRESHOLD = const(0x03)
ADS1X15_CONFIG_OS_SINGLE = const(0x8000)
ADS1X15_CONFIG_MUX_OFFSET = const(12)
# Maping of gain values to config register values.
ADS1X15_CONFIG_GAIN = {
2/3: 0x0000,
1: 0x0200,
2: 0x0400,
4: 0x0600,
8: 0x0800,
16: 0x0A00
}
ADS1X15_PGA_RANGE = {
2/3: 6.144,
1: 4.096,
2: 2.048,
4: 1.024,
8: 0.512,
16: 0.256
}
ADS1X15_CONFIG_MODE_CONTINUOUS = const(0x0000)
ADS1X15_CONFIG_MODE_SINGLE = const(0x0100)
# Mapping of data/sample rate to config register values for ADS1015 (faster).
ADS1015_CONFIG_DR = {
128: 0x0000,
250: 0x0020,
490: 0x0040,
920: 0x0060,
1600: 0x0080,
2400: 0x00A0,
3300: 0x00C0
}
# Mapping of data/sample rate to config register values for ADS1115 (slower).
ADS1115_CONFIG_DR = {
8: 0x0000,
16: 0x0020,
32: 0x0040,
64: 0x0060,
128: 0x0080,
250: 0x00A0,
475: 0x00C0,
860: 0x00E0
}
ADS1X15_CONFIG_COMP_WINDOW = const(0x0010)
ADS1X15_CONFIG_COMP_ACTIVE_HIGH = const(0x0008)
ADS1X15_CONFIG_COMP_LATCHING = const(0x0004)
ADS1X15_CONFIG_COMP_QUE = {
1: 0x0000,
2: 0x0001,
4: 0x0002
}
ADS1X15_CONFIG_COMP_QUE_DISABLE = const(0x0003)
ADS1X15_DIFF_CHANNELS = {
(0,1): 0,
(0,3): 1,
(1,3): 2,
(2,3): 3
}
# pylint: enable=bad-whitespace
[docs]class ADC_Channel(object):
"""Provides per channel access to ADC readings."""
def __init__(self, adc, channel):
self._adc = adc
self._channel = channel
@property
def value(self, ):
"""ADC reading in raw counts."""
return self._adc._read_channel(self._channel) # pylint: disable=protected-access
@property
def volts(self, ):
"""ADC reading in volts."""
return self._adc._read_channel_volts(self._channel) # pylint: disable=protected-access
[docs]class ADS1x15(object):
"""Base functionality for ADS1x15 analog to digital converters."""
def __init__(self, i2c, address=ADS1X15_DEFAULT_ADDRESS):
self.buf = bytearray(3)
self.i2c_device = I2CDevice(i2c, address)
self.bits = None
self._channels = [ADC_Channel(self, 0),
ADC_Channel(self, 1),
ADC_Channel(self, 2),
ADC_Channel(self, 3)]
def _write_register(self, reg, value):
"""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):
"""Return 16 bit register value as tuple of (LSB, MSB)."""
self.buf[0] = reg
with self.i2c_device as i2c:
i2c.write(self.buf, end=1, stop=False)
i2c.readinto(self.buf, start=1)
return self.buf[1] << 8 | self.buf[2]
def _data_rate_default(self):
"""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 _data_rate_config(self, data_rate):
"""Subclasses should override this function and return a 16-bit value
that can be OR'ed with the config register to set the specified
data rate. If a value of None is specified then a default data_rate
setting should be returned. If an invalid or unsupported data_rate is
provided then an exception should be thrown.
"""
raise NotImplementedError('Subclass must implement _data_rate_config function!')
def _conversion_value(self, low, high):
"""Subclasses should override this function that takes the low and high
byte of a conversion result and returns a signed integer value.
"""
raise NotImplementedError('Subclass must implement _conversion_value function!')
def _read_channel(self, channel):
"""Subclasses should override this function to return a value for the
requested channels as a signed integer value.
"""
raise NotImplementedError('Subclass must implement _read_channel function!')
def _read_channel_volts(self, channel):
"""Subclasses should override this function to return a value for the
requested channels as a float value.
"""
raise NotImplementedError('Subclass must implement _read_channel_volts function!')
def _conversion_complete(self):
"""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
def _read(self, mux, gain, data_rate, mode):
"""Perform an ADC read with the provided mux, gain, data_rate, and mode
values. Returns the signed integer result of the read.
"""
config = ADS1X15_CONFIG_OS_SINGLE # Go out of power-down mode for conversion.
# Specify mux value.
config |= (mux & 0x07) << ADS1X15_CONFIG_MUX_OFFSET
# Validate the passed in gain and then set it in the config.
if gain not in ADS1X15_CONFIG_GAIN:
raise ValueError('Gain must be one of: 2/3, 1, 2, 4, 8, 16')
config |= ADS1X15_CONFIG_GAIN[gain]
# Set the mode (continuous or single shot).
config |= mode
# Get the default data rate if none is specified (default differs between
# ADS1015 and ADS1115).
if data_rate is None:
data_rate = self._data_rate_default()
# Set the data rate (this is controlled by the subclass as it differs
# between ADS1015 and ADS1115).
config |= self._data_rate_config(data_rate)
config |= ADS1X15_CONFIG_COMP_QUE_DISABLE # Disble comparator mode.
# Send the config value to start the ADC conversion.
self._write_register(ADS1X15_POINTER_CONFIG, config)
# Wait for conversion to complete
while not self._conversion_complete():
time.sleep(0.01)
# Return the result
return self.get_last_result()
[docs] def stop_adc(self):
"""Stop all continuous ADC conversions (either normal or difference mode).
"""
# Set the config register to its default value of 0x8583 to stop
# continuous conversions.
self._write_register(ADS1X15_POINTER_CONFIG, 0x8583)
[docs] def get_last_result(self):
"""Read the last conversion result when in continuous conversion mode.
Will return a signed integer value.
"""
# Retrieve the conversion register value, convert to a signed int, and
# return it.
result = self._read_register(ADS1X15_POINTER_CONVERSION)
return self._conversion_value(result & 0xff, result >> 8)