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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.
# Explicitly break the 16-bit value down to a big endian pair of bytes.
self._device.writeList(ADS1x15_POINTER_CONFIG, [(config >> 8) & 0xFF, config & 0xFF])
# Wait for the ADC sample to finish based on the sample rate plus a
# small offset to be sure (0.1 millisecond).
time.sleep(1.0/data_rate+0.0001)
# Retrieve the result.
result = self._device.readList(ADS1x15_POINTER_CONVERSION, 2)
return self._conversion_value(result[1], result[0]) |
