Part Number: ADS1115
Hi there, I'm using an ADS1115 analogue-digital converter, with 5V supply voltage, with gain set to +-6.144V (I'm reading values between 0.5 and 5 volts, in single-ended mode on three channels of my four).
I seem to be having an issue where when I read one channel, it returns the value associated with the conversion for the previous channel.
I have tried to add a delay in the Adafruit ADS1x15 library between writing the configuration and reading from the conversion register.
However, this does not seem to have resolved my issue. I will post the library code I have below. Does anyone mind taking a quick look and suggesting where I might want to try adding a delay or implementing another change that may help?
Thank you so much.
CircuitPython base class driver for ADS1115
from micropython import const
from adafruit_bus_device.i2c_device import I2CDevice
import time
_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
}
from micropython import const
from adafruit_bus_device.i2c_device import I2CDevice
import time
_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
}
class Mode:
# values here are masks for setting MODE bit in Config Register
CONTINUOUS = 0x0000
SINGLE = 0x0100
class ADS1x15(object):
"""Base functionality for ADS1x15 analog to digital converters."""
def __init__(self, i2c, gain=1, data_rate=None, mode=Mode.SINGLE,
address=_ADS1X15_DEFAULT_ADDRESS):
#pylint: disable=too-many-arguments
self._last_pin_read = None
self.buf = bytearray(3)
self._data_rate = self._gain = self._mode = None
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 data_rate(self):
"""The data rate for ADC conversion in samples per second."""
return self._data_rate
@data_rate.setter
def data_rate(self, rate):
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):
"""Possible data rate settings."""
raise NotImplementedError('Subclass must implement rates property.')
@property
def rate_config(self):
"""Rate configuration masks."""
raise NotImplementedError('Subclass must implement rate_config property.')
@property
def gain(self):
"""The ADC gain."""
return self._gain
@gain.setter
def gain(self, gain):
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):
"""Possible gain settings."""
g = list(_ADS1X15_CONFIG_GAIN.keys())
g.sort()
return g
@property
def mode(self):
"""The ADC conversion mode."""
return self._mode
@mode.setter
def mode(self, mode):
if mode != Mode.CONTINUOUS and mode != Mode.SINGLE:
raise ValueError("Unsupported mode.")
self._mode = mode
def read(self, pin, is_differential=False):
pin = pin if is_differential else pin + 0x04
return self._read(pin)
def _data_rate_default(self):
raise NotImplementedError('Subclasses must implement _data_rate_default!')
def _conversion_value(self, raw_adc):
raise NotImplementedError('Subclass must implement _conversion_value function!')
def _read(self, pin):
"""Perform an ADC read. Returns the signed integer result of the read."""
data_rate = self.data_rate
fast = True
if self._last_pin_read != pin:
self._last_pin_read = pin
fast = False
config = _ADS1X15_CONFIG_OS_SINGLE
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
#time.sleep(1.0/data_rate+0.0001)
self._write_register(_ADS1X15_POINTER_CONFIG, config)
#if self.mode == Mode.SINGLE:
while not self._conversion_complete():
pass
return self._conversion_value(self.get_last_result(fast))
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 get_last_result(self, fast=False):
"""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, 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, fast=False):
"""Read 16 bit register value. If fast is True, the pointer register
is not updated.
"""
self.buf[0] = reg
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, stop=False)
return self.buf[0] << 8 | self.buf[1]
