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Explore the fascinating journey of transforming a classic German FeTAp 611 rotary phone into a modern mobile device in this 34-minute conference talk from 39C3. Discover how to bridge analog and digital worlds while maintaining the vintage charm and functionality that would make your grandparents comfortable using the device. Learn about the technical challenges of implementing German analog telephony standard 1TR110-1 on a battery-powered system, including the design of a state machine on an STM32 microcontroller and the integration of old carbon microphones with modern audio electronics. Delve into the complexities of designing a flyback-based SMPS to generate 32V-75V ringing voltage, creating 25Hz AC using an H-bridge, and clever PCB layout techniques that repurpose the ancient second handset connector for USB-C charging. Understand the design goals of creating a grandparents-compatible device with easy phone switching capabilities, standard components for reasonable manufacturing costs, and device-agnostic circuit design that can adapt to different vintage phone models like W48, FeTAp 791, and FeTAp 611. Gain insights into both the technical aspects of retrofitting vintage electronics and the amusing social reactions when such a device unexpectedly rings in public spaces like flea markets.
