A basic introduction to the encoding and decoding of the phone dial tones using Dual-Tone Multi-frequency signaling.
You have certainly used a phone before. But, have you ever wondered about the secret of the sounds you hear while typing a number to call, the subject has an old history.
It started back in the time of analog phones. The dialed number to send over the line was not sent in the form of a digital signal, but rather in its analog fomat. This jupyter notebook illustrates some simple methods to code and decode the DTMF tones. The code is not a product-ready code as it does not work in the real-world situation, but it is a simple illustration if you want to understand the concepts behind the topic.
Here is a helpful wikipedia page if you want to learn more about the topic:
https://en.wikipedia.org/wiki/Dual-tone_multi-frequency_signaling