Old-school Rotary Phone gets GSM Upgrade

Sometimes, the answer to, “Why would you bother with a project like that?” is just as simple as, “Because it’s cool.” We suspect that was the motivation behind [Dirk-Jan]’s project to make portable versions of classic rotary telephones.

On style points alone, [Dirk-Jan] scores big. The mid-1950s vintage Belgian RTT model 56 phone has wonderful lines in its Bakelite case and handset and a really cool flip-up bail to carry it around, making it a great choice for a portable. The guts of the phone were replaced with a SIM900 GSM module coupled with a PIC microcontroller and an H-bridge to drive the ringer solenoids, along with a Li-ion battery and charger to keep it totally wireless – except for the original handset cord, of course. The video after the break show the phone in action both making and receiving calls; there’s something pleasing on a very basic level about the sound of a dial tone and the gentle ringing of the bell. And it may be slow, but a rotary dial has plenty of tactile appeal too.

Rotary-to-cell conversions are a popular “just because” project, like this conversion designed to allow an angry slam-down of the handset. The orange Siemens phone in that project is nice and all, but we really favor the ’50s look for a portable.

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Rotary and cordless phones mashup

This pile of hardware marries telecommunications hardware from distinctly different generations. [Andrew D. Farquharson] wanted the retro look and operation of a rotary phone, with the convenience of a modern cordless. He combined the two technologies to achieve his goal.

The first problem was to find a way to translate the rotary inputs to something he could use. There are already a bunch of projects that use rotary hardware so he didn’t have to reinvent the wheel. He followed this guide to connecting Arduino to a rotary phone.

The next step was to interface with his cordless phone. He ditched the case and soldered rainbow ribbon cable to the entire button matrix. An opto-isolator is used to protect the Arduino while making each connection. Finally, he patched into the mechanism which monitors the cradle to see if the handset has been picked up. It sounds like his code lets you enter the number on the dial, then pick up the handset to actual transmit it through the cordless phone.