kvdijken / thd2

thd.py

thd.py is a program to calculate Total Harmonic Distortion from a signal which is taken from a Siglent oscilloscope while also showing a live Fast Fourier Transform display and showing markers for fundamental and harmonic frequencies.

A screen recording of a typical out is shown in thd.mps in the folder resources/.

This program has been tested on a Siglent SDS1202X-E oscilloscope, but is supposed to work on any SDS1000 and SDS2000 series oscilloscopes from Siglent. This is determined by the pydatacq package which is imported by thd.py.

communication

The program communicates SCPI over ethernet with the oscilloscope, ie. the oscilloscope needs to be connected to ethernet and have an ip-address known to the user. The ip address can be entered on the commandline to start the the program.

frequency input

Frequency input on the commandline can be done in human legible form, like 97.5M for 97500000, or 1.5k for 1500. This is done using the package 'quantiphy'.

Entering python3 thd.py --help will show the following information:

usage: thd.py [-h] -C {1,2} [-f0 FREQ] [-max_f FREQ] [-f FLOOR] -ip IP [-port PORT] [-t NAME] [-w NAME]
              [-fps]

Display FFT and calculate THD for a channel on Siglent SDS1202X-E oscilloscope.

options:
  -h, --help            show this help message and exit
  -C {1,2}              channel to display (default: None)
  -f0 FREQ              fundamental frequency (in Hz) (default: 1k)
  -max_f FREQ           maximum frequency to display / use for calculations (in Hz) (default: 25k)
  -f FLOOR, --floor FLOOR
                        minimum level of harmonics (in dBvrms) (default: -85)
  -ip IP                ip address of the oscilloscope (default: None)
  -port PORT            port on which the oscilloscope is listening (default: 5025)
  -t NAME, --title NAME
                        plot title (default: None)
  -w NAME, --window NAME
                        window title (default: None)
  -fps                  show waveform updates per second (default: False)

requirements

The following packages are required for fft.py to run:

• pydatacq
• numpy
• scipy
• quantiphy
• matplotlib
• uvloop