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mdac_attenuator.py
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mdac_attenuator.py
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# -*- coding: utf-8 -*-
import digitalio
import time
from adafruit_bus_device import spi_device
class MdacAttenuator(object):
'''
Manages an MDAC attenuator via SPI
'''
def __init__(self, spi, cs, baudrate=1000000, debug=False, steps=200, attenuation_slope=40):
self.level = 0
self.levels = []
self.attenuation_slope = attenuation_slope
self.steps = steps
self.dac_value = None
self.debug = debug
self._device = spi_device.SPIDevice(spi, cs, baudrate=baudrate, polarity=0, phase=0)
self._write_dac_value(0)
self._calculate_levels()
self._print('initialed with {0} levels'.format(len(self.levels)))
def _print(self, message):
'''
Small function for printing information is debug option is enabled
'''
if not self.debug:
return
else:
print('mdac-attenuator: {0}'.format(message))
def _write_dac_value(self, value):
'''
Sets the MDAC value
'''
if value < 0 or value >= 65536:
self._print('dac value must be between 0 and 65535. Given value {0}'.format(value))
return
with self._device as device:
high_byte, low_byte = divmod(value, 256)
device.write(bytearray([3]))
device.write(bytearray([high_byte]))
device.write(bytearray([low_byte]))
self.dac_value = value
self._print('set DAC value: {0}'.format(value))
def _calculate_levels(self):
'''
Calculates a list of linear values for a logarithmic scale
'''
for i in range(self.steps):
self.levels.append(round((10**-(i/self.attenuation_slope)) * 65536))
self.levels[0] = 0
self.levels[-1] = 65535
self.level_max = len(self.levels) - 1
self.levels = list(set(self.levels))
self.levels.sort()
def set_level(self, level):
'''
Sets an attenuation level
'''
if level > self.level_max or level < 0:
self._print('level must be between 0 and {0}. Given level {1}'.format(self.level_max, level))
return
self._write_dac_value(self.levels[level])
self.level = level
self._print('set level: {0}'.format(self.level))
def up(self):
'''
Increases level
'''
self.set_level(self.level + 1)
def down(self):
'''
Decreases level
'''
self.set_level(self.level - 1)