Morse Code Generator for macOS
Click on the icon to download the Morse Code Generator application for macOS 10.15.7 Catalina.
I did some research how to filter an audio signal of a specific frequency, in example 1000 Hz, out of an audio signal with a spectrum of 50 Hz to 10 kHz. The first method to filter a specific frequency out of an audio spectrum I thought of was to use Digital Signal Processing (DSP) and a discrete Fast Fourier Transformation (FFT).
Because DSP works with digital signals the analog audio signal has to be converted to a digital audio signal.
With the use of DSP)and the Fast Fourier Transformation it’s possible to detect the presence of a specified frequency for instance a 1000 Hz audio signal. However, this requires a lot of processor power which is not available in an Atmel 328 microprocessor.
In order not to overload the microprocessor it should be a better solution to send a digital on/off signal to the processor so that the microprocessor’s only job is to decode the digital signal and displays the decoded text on a display.
Instead of decoding the analog signal with a microprocessor I did a test with a tone decoder i.c. LM567. To test the LM567 I used my application Audio Graphic Tool as LF-generator. The test went well and I decide to do a test with a MORSE-signal.
With Audio Graphic Tool as a starting point I build an application that generates a MORSE signal. I searched the internet for an Arduino application (Atmel 328 microprocessor) that could detect MORSE code and to my surprise I found an application that works fine.
It not only works fine but it detects MORSE direct from an audio signal without overloading the Atmel 328. The application don’t use a FFT to detect the audio signal of a specified frequency but ‘The Goertzel Algoritme’ which is simpler and faster.
The Goertzel Algoritme is fast enough for MORSE but for NAVTEX I think it might be to slow.
Last update: April 9, 2021