Machine Learning and a Raspberry Pi Inside a Classic 1970’s GPO Telephone

Alasdair Allan
3 min readSep 25, 2017

Inspired by the 1986 Google Pi Intercom build put together Martin Mander, I’d been thinking about venturing beyond the cardboard box, and building my own retro-computing enclosure around the Google AIY Projects Voice Kit for a while now.

I recently came across the GPO 746 Rotary Telephone and picked up a couple “just in case.” This is a modern day replica of what must be the most iconic rotary dial phone here in the United Kingdom. This is the phone that sat on everybody’s desk, and in their front halls, throughout the 1970’s.

It would, in other words, make a perfect enclosure for the Voice Kit.

The AIY Projects-enabled GPO 746 rotary phone beside a “stock” AIY Projects Voice Kit. (📷: Alasdair Allan)

Ahead of the new Voice Kit hitting the shelves in October I managed to get my hands on a few pre-production kits. The challenge was to integrate one of them with the GPO 746 in a way that made it still look and feel like a phone, and that meant ripping out most of the existing electronics.

Since the line voltage in the UK is +50V, pretty much none of the electronics inside the phone were going to be useful. So after disposing of most of the internals I set about rewiring the phone for the Voice Kit.

All the new wiring in place and working.

The real point of a build like this is try and make the new technology comfortably sit amongst the old. That means adding effects like dial tones, and the ‘clicking’ noises you used to get with the pulse dialling telephones, to make it feel more authentic.

The final build.

I’ve written up all details of the build including a walkthrough of how I tore down the phone and integrated the Voice Kit, and posted the source code which adds those little touches—like the dial tone and the hang up noises—to the build that makes it not just look, but also feel, like you’re using a rotary phone.

Available to Preorder

The new AIY Projects Voice Kits are being produced by Google, and are available to pre-order at Micro Center. The kit is priced at $25 on its own, but you can also pick one up for free if you order a Raspberry Pi 3 at $35 for in-store pickup from Micro Center.

The Voice Kit will also be available through resellers like Adafruit, and Seeed Studio. In the United Kingdom it’s being made available through Pimoroni, and will cost £25, and you can expect shipping dates for kits ordered in through them to be similar to those ordered from Micro Center.

The new kits should hit shelves in October.

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