Cut the Cord and Add Cellular Connectivity to a Retro Rotary Phone

Creator “dancejic” and family stopped having a corded home phone many years ago. While many simply rely on a new phone number or numbers, this family’s “home” number now exists only in an extra SIM card.

This worked OK with dancejic’s dual-SIM phone, however, still caused a few problems. Namely, when older parents visited without a cell phone, and there was no way to call them when away. The inconveniences were exacerbated after switching to a single-SIM phone, so as a fun and practical project, this cellular-based rotary phone was born.

The fun part was of course the rotary aspect of the build, which is unknown to most younger people, and gave denejic’s son who also worked on this project, a chance to “experience” this rather obsolete technology. The original idea was to find and reuse an old rotary phone, but per current visiting restrictions, they instead opted for a new model from Amazon. It conveniently features a * and # option, and still looks sufficiently “retro,” so there were some benefits to this route.

A Raspberry Pi Zero W was stuffed into the phone’s chassis, along with a GSM/GPRS HAT that could take care of communications and accommodate the needed SIM card. Audio signals are passed to and from the headset through a 3.5mm headphone jack inside the phone. The rotary mechanism is attached to the Pi and translated appropriately via software, with signals from the handset "hook" switch. SMS messages are simply forwarded to another phone, and ringing is taken care of by a battery-powered recordable sound module.

The phone looks like an interesting and potentially useful build. Much more info, including code, is available in the project's write-up.