A simple filter library written in micro python for use in microcontrollers like esp8266, esp32.

The filters.py library contains three types of filters:

• Average filter
• EWMA filter
• IIR filter

Usage

Model of operation of filter functions: the first call to the NAME_filter function returns the value given as the input parameter input. This value is also stored for the next calculations for the next calls of this function. Next calls of this function continue calculations for input data for previously set filter parameters or defaults values (if parameters are not set). Using the NAME_filter_reset function returns this state to the beginning.

example code

# import library
import filters
# create sample input data table
input_data = [1, 2, 1, 4, 3, 4, 5, 2, 1, 2]
# create object
filtered = filters.filter
# set filter parameter
filtered.ewma_filter_reset(0.2)
# print input and filtered values
for i in range ( len(input_data) ):
  print('input= ' + input_data[i] + ' output= ' + filtered.ewma_filter(input_data[i]) )

other examples

link to more advanced examples

Average filter

average_filter_reset(nums=1)

Function resets the filter to initial state with optional parameter nums (if omnitet then default set 1 samples average calculation).

average_set_samples(nums)

The function sets the number of data samples for which the mathematical mean will be calculated. nums must be greather or equal 1.

average_filter(input)

The function returns the calculated value for the given input data.

IIR filter

iir_filter_reset(factor=1)

Function resets the filter to initial state with optional parameter factor (if omnitet then default value of factor is set to 1).

iir_set_factor(factor)

The function sets the factor parameter. factor must be greather or equal 1 and should not exceed the value of 32. The factor must be an integer.

iir_filter(input)

The function returns the calculated value for the given input data.

EWMA filter

ewma_filter_reset(alpha=1)

Function resets the filter to initial state with optional parameter alpha (if omnitet then default value of alpha is set to 1).

ewma_set_alpha(alpha)

The function sets the alpha parameter. alpha must be in range (0 < alpha < 1).

ewma_filter(input)

The function returns the calculated value for the given input data.

Graphical representation of Average filter working

How the nums of samples parameter affects the output.

X axis - number of data sample

Y axis - data value

Graphical representation of EWMA filter working

How the alpha parameter affects the output.

X axis - number of data sample

Y axis - data value

Graphical representation of IIR filter working

How the factor parameter affects the output.

X axis - number of data sample

Y axis - data value