Horst Gether @ edn.com writes about how the simple and well established 3.5mm jack can be used for data-rich communication between headset and mobile device.
The 3.5mm phone jack is a well-established standard in the audio industry and continues to get strong support from users in the market. Originally invented in the 19th century for telephone switch boards, it made its way into mobile phones, tablets, and personal computers to connect audio and communication headsets for phone calls or simply for listening to music. While the phone jack has a rather long evolutionary history, the functionality that the 3.5mm four-pole accessory device provides to its end customers is rather limited.
Data-rich 3.5mm jack vies with USB-C for headsets – [Link]