To use:

import filters 

Module filters

This module allows you to filter sensor data using various linear and non-linear filtering techniques.

# A class to perform simple first order high pass filtering on a sensor value
class HighPassFilter
    # Create a high pass filter object with a given alpha. 
    def __init__(self,alpha)

    # Process a new value with this filter object and return the output value
    def on_value(self,value_in)

    # Make a high-pass filter with this cutoff frequency.
    @staticmethod
    def make_from_cutoff(cutoff_frequency,time_between_samples)

    # Make a high-pass filter with a particular time constant
    @staticmethod
    def make_from_time_constant(time_constant,time_between_samples)


# A class to perform simple first order lowpass filtering on a sensor value
class LowPassFilter
    # Create a low pass filter object with a given alpha. 
    def __init__(self,alpha)

    # Process a new value with this filter object and return the output value
    def on_value(self,value_in)

    # Make a low-pass filter with this cutoff frequency .
    @staticmethod
    def make_from_cutoff(cutoff_frequency,time_between_samples)

    # Make a low-pass filter with a particular time constant.
    @staticmethod
    def make_from_time_constant(time_constant,time_between_samples)


# A class to perform median filtering on a sensor value
class MedianFilter
    # Create a median filter object with a given block size
    def __init__(self,block_size)

    # Process a new value with this filter object and return the output value
    def on_value(self,new_value)


# A class to perform a sliding average (mean)
class SlidingAverageFilter
    # Create a sliding average object with a given block size
    def __init__(self,block_size)

    # Process a new value with this filter object and return the output value
    def on_value(self,new_value)


# A class to perform a mean (average) on blocks of sensor data
class BlockMeanFilter
    # Process a new value with this filter object and return the output value
    def on_value(self,new_value)


# A class to perform a median over blocks of sensor values.
class BlockMedianFilter
    # Process a new value with this filter object and return the output value
    def on_value(self,new_value)


# A class to perform a maximum on blocks of data
class BlockMaxFilter
    # Process a new value with this filter object and return the output value
    def on_value(self,new_value)


# A class to perform a minimum on blocks of data
class BlockMinFilter
    # Process a new value with this filter object and return the output value
    def on_value(self,new_value)

class filters.HighPassFilter

class HighPassFilter:
    # Create a high pass filter object with a given alpha. 
    def __init__(self,alpha)

    # Process a new value with this filter object and return the output value
    def on_value(self,value_in)

    # Make a high-pass filter with this cutoff frequency.
    @staticmethod
    def make_from_cutoff(cutoff_frequency,time_between_samples)

    # Make a high-pass filter with a particular time constant
    @staticmethod
    def make_from_time_constant(time_constant,time_between_samples)

Description

A class to perform simple first order high pass filtering on a sensor value

filters.HighPassFilter.init

# filters.HighPassFilter.__init__
def __init__(
    self,
    alpha
)

Create a high pass filter object with a given alpha.

You may want to calculate alpha based on cutoff frequency or time constant, in that case, you can use the static methods make_from_cutoff and make_from_time_constant to make the filter instead of using the constructor.

Parameters

• alpha(float)
  The filter constant alpha

Returns

• filter(HighPassFilter)
  A high pass filter object

filters.HighPassFilter.on_value

# filters.HighPassFilter.on_value
def on_value(
    self,
    value_in
)

Process a new value with this filter object and return the output value

Parameters

• value_in(float)
  Input value to filter

Returns

• filtered_value(float)
  Filter output value

filters.HighPassFilter.make_from_cutoff

# filters.HighPassFilter.make_from_cutoff
@staticmethod
def make_from_cutoff(
    cutoff_frequency,
    time_between_samples
)

Make a high-pass filter with this cutoff frequency.

Parameters

• cutoff_frequency(float)
  Cutoff frequency in HZ
• time_between_samples(float)
  seconds between samples

Returns

• filter(HighPassFilter)
  High-pass filter object

filters.HighPassFilter.make_from_time_constant

# filters.HighPassFilter.make_from_time_constant
@staticmethod
def make_from_time_constant(
    time_constant,
    time_between_samples
)

Make a high-pass filter with a particular time constant

Parameters

• time_constant(float)
  Time constant in seconds
• time_between_samples(float)
  Seconds between samples

Returns

• filter(HighPassFilter)
  High-pass filter object

class filters.LowPassFilter

class LowPassFilter:
    # Create a low pass filter object with a given alpha. 
    def __init__(self,alpha)

    # Process a new value with this filter object and return the output value
    def on_value(self,value_in)

    # Make a low-pass filter with this cutoff frequency .
    @staticmethod
    def make_from_cutoff(cutoff_frequency,time_between_samples)

    # Make a low-pass filter with a particular time constant.
    @staticmethod
    def make_from_time_constant(time_constant,time_between_samples)

Description

A class to perform simple first order lowpass filtering on a sensor value

filters.LowPassFilter.init

# filters.LowPassFilter.__init__
def __init__(
    self,
    alpha
)

Create a low pass filter object with a given alpha.

You may want to calculate alpha based on cutoff frequency or time constant, in that case, you can use the static methods make_from_cutoff and make_from_time_constant to make the filter instead of using the constructor.

Parameters

• alpha(float)
  The filter constant alpha

Returns

• filter(LowPassFilter)
  A low pass filter object

filters.LowPassFilter.on_value

# filters.LowPassFilter.on_value
def on_value(
    self,
    value_in
)

Process a new value with this filter object and return the output value

Parameters

• value_in(float)
  Input value to filter

Returns

• filtered_value(float)
  Filter output value

filters.LowPassFilter.make_from_cutoff

# filters.LowPassFilter.make_from_cutoff
@staticmethod
def make_from_cutoff(
    cutoff_frequency,
    time_between_samples
)

Make a low-pass filter with this cutoff frequency .

Parameters

• cutoff_frequency(float)
  Cutoff frequency in HZ
• time_between_samples(float)
  Seconds between samples

Returns

• filter(LowPassFilter)
  Low-pass filter object

filters.LowPassFilter.make_from_time_constant

# filters.LowPassFilter.make_from_time_constant
@staticmethod
def make_from_time_constant(
    time_constant,
    time_between_samples
)

Make a low-pass filter with a particular time constant.

Parameters

• time_constant(float)
  Time constant in seconds
• time_between_samples(float)
  Seconds between samples

Returns

• filter(LowPassFilter)
  Low-pass filter object

class filters.MedianFilter

class MedianFilter:
    # Create a median filter object with a given block size
    def __init__(self,block_size)

    # Process a new value with this filter object and return the output value
    def on_value(self,new_value)

Description

A class to perform median filtering on a sensor value

filters.MedianFilter.init

# filters.MedianFilter.__init__
def __init__(
    self,
    block_size
)

Create a median filter object with a given block size

Parameters

• block_size(int)
  The number of previous samples that we take a median over

filters.MedianFilter.on_value

# filters.MedianFilter.on_value
def on_value(
    self,
    new_value
)

Process a new value with this filter object and return the output value

Parameters

• value_in(float)
  Input value to filter

Returns

• filtered_value(float)
  Median of current sliding buffer

class filters.SlidingAverageFilter

class SlidingAverageFilter:
    # Create a sliding average object with a given block size
    def __init__(self,block_size)

    # Process a new value with this filter object and return the output value
    def on_value(self,new_value)

Description

A class to perform a sliding average (mean) on a sensor value

filters.SlidingAverageFilter.init

# filters.SlidingAverageFilter.__init__
def __init__(
    self,
    block_size
)

Create a sliding average object with a given block size

Parameters

• block_size(int)
  The number of previous samples that we sliding average over

filters.SlidingAverageFilter.on_value

# filters.SlidingAverageFilter.on_value
def on_value(
    self,
    new_value
)

Process a new value with this filter object and return the output value

Parameters

• value_in(float)
  Input value to filter

Returns

• filtered_value(float)
  Mean of current sliding average buffer

class filters.BlockMeanFilter

class BlockMeanFilter:
    # Process a new value with this filter object and return the output value
    def on_value(self,new_value)

Description

A class to perform a mean (average) on blocks of sensor data

Sensor values are only output once per block_size input samples.

filters.BlockMeanFilter.on_value

# filters.BlockMeanFilter.on_value
def on_value(
    self,
    new_value
)

Process a new value with this filter object and return the output value

Parameters

• value_in(float)
  Input value to filter

Returns

• filtered_value(float)
  Mean of the current block, or None if we are mid-block

class filters.BlockMedianFilter

class BlockMedianFilter:
    # Process a new value with this filter object and return the output value
    def on_value(self,new_value)

Description

A class to perform a median over blocks of sensor values.

Sensor values are only output once per block_size input samples.

filters.BlockMedianFilter.on_value

# filters.BlockMedianFilter.on_value
def on_value(
    self,
    new_value
)

Process a new value with this filter object and return the output value

Parameters

• value_in(float)
  Input value to filter

Returns

• filtered_value(float or None)
  Median of the current block, or None if we are mid block

class filters.BlockMaxFilter

class BlockMaxFilter:
    # Process a new value with this filter object and return the output value
    def on_value(self,new_value)

Description

A class to perform a maximum on blocks of data

Sensor values are only output once per block_size input samples.

filters.BlockMaxFilter.on_value

# filters.BlockMaxFilter.on_value
def on_value(
    self,
    new_value
)

Process a new value with this filter object and return the output value

Parameters

• value_in(float)
  Input value to filter

Returns

• filtered_value(float)
  Maximum of this block, or None if mid block

class filters.BlockMinFilter

class BlockMinFilter:
    # Process a new value with this filter object and return the output value
    def on_value(self,new_value)

Description

A class to perform a minimum on blocks of data

Sensor values are only output once per block_size input samples.

filters.BlockMinFilter.on_value

# filters.BlockMinFilter.on_value
def on_value(
    self,
    new_value
)

Process a new value with this filter object and return the output value

Parameters

• value_in(float)
  Input value to filter

Returns

• filtered_value(float or None)
  Minimum of this block, or None if mid block