2.5 FFT Module API Manual

1. Overview

The FFT (Fast Fourier Transform) module is used to perform a Fourier transform on input time-domain data, converting it into frequency-domain data and returning the corresponding frequency magnitudes. Through FFT operations, time-domain signals can be effectively transformed into frequency-domain signals, facilitating the analysis of the signal’s frequency components.

2. API Introduction

The FFT module provides an FFT class, supporting three main functions: run(), freq(), and amplitude(), which are used for performing Fast Fourier Transform, frequency calculation, and amplitude calculation, respectively.

2.1 Class machine.FFT

Description

This class is used to create an FFT object and perform the Fourier transform on the input data.

Syntax

from machine import FFT
import array

# Define time-domain data
data = array.array('i', [1, 2, 3, 4, 5, 6, 7, 8])

# Create an FFT object, perform a 64-point FFT operation, with an offset of 0
fft1 = FFT(data, 64, 0)

Parameters

Parameter Name	Description	Type	Input/Output
data	Input time-domain data, of type bytearray.		Input
points	Number of points for the FFT operation, supports 64, 128, 256, 512, 1024, 2048, and 4096 points.		Input
shift	Data offset, default is 0.		Input

Return Values

Return Value	Description
0	Operation successful.
Non-zero	Operation failed.

2.1.1 run() Method

Description

This function is used to obtain the frequency-domain data after the Fourier transform.

Syntax

res = fft1.run()

Parameters

None

Return Values

Return Value	Description
res	Returns a list containing the frequency-domain data, which includes points tuples, each containing 2 elements: the real part and the imaginary part.

2.1.2 freq() Method

Description

This function is used to obtain the calculated frequency values.

Syntax

res = FFT.freq(points, sample_rate)

Parameters

Parameter Name	Description	Input/Output
points	Number of points involved in the FFT operation.	Input
sample_rate	Data sampling rate.	Input

Return Values

Return Value	Description
res	Returns a list containing the frequency values for each frequency point.

2.1.3 amplitude() Method

Description

This function is used to calculate the amplitude of each frequency point. It is mainly used for testing purposes, and users can write more complex amplitude processing functions in Python.

Syntax

amp = FFT.amplitude(FFT_res)

Parameters

Parameter Name	Description	Input/Output
FFT_res	The FFT calculation result returned by the run() function.	Input

Return Values

Return Value	Description
amp	Returns a list containing the amplitude of each frequency point.