Rotary Phone Gets Bluetooth Upgrade

Rotary dial phones have a certain romantic charm about them; something never quite captured in the post-Touch Tone era. With landline phone services less popular than ever, these old workhorses aren’t really cut out for daily use anymore. However, with a modern brain transplant, they can still get the job done just fine.

[Xabier Zubizarreta] has undertaken to retrofit his FeTAp-611 rotary phone with a Bluetooth rig, allowing it to be used with smartphones to place and receive calls. A Raspberry Pi Zero W serves as the brains of the operation, chosen for its compact size and onboard Bluetooth and WiFi. Getting the Pi to work effectively with an Android phone as a Bluetooth audio device requires some trickery, but it’s nothing that can’t be fixed by custom compiling a few off-the-shelf tools. [Xabier]’s next big hurdle is finding a tidy way to generate a 30 VAC signal to drive the original ringer, something that proves difficult for most similar projects.

We love to see these telecommunication relics kept ticking, so if you happen to be building a vintage telephone exchange in your garden shed – be sure to let us know.

7 thoughts on “Rotary Phone Gets Bluetooth Upgrade

  1. For producing the appropriate voltages at the necessary AC frequency for driving an old-style ringer, there are off-the-shelf components to do just that. I used a PowerDsine ringing generator off eBay a while ago – no idea who I bought mine from, but there are some identical-looking parts here. Lots of other sellers appear to be available.

    12V DC input, 70VAC 20Hz output. Mine has a ~5V input which will suppress ringing, which is super-handy for driving from more modern electronics. A 3.3V output from a Raspberry Pi isn’t enough – I did some disgusting things with a transistor. I think. It’s been a while.

    (I was building a wireless SIP phone with a Raspberry Pi. I got most of it running, then got distracted – here’s it in its Arduino prototyping stages with the dial, hook and ringer all working. The Bluetooth stuff described sounds really interesting – I think I may just resurrect my own project as a peripheral for my mobile phone!)

  2. > Rotary dial phones have a certain romantic charm about them

    … just like mediaval torturing devices.

    Really, those nerve-wreckingly slow dials that would sometimes hang at the wrong number, the loud noise they made when dialing – I hated them when I had no alternative (because THERE WAS NO ALTERNATIVE) and I hated them even more when the first touch tone phones were available. My friend and I were quite good at dialing WITHOUT using the front dials, by simply hammering on the hook at the right speed.

    Not everything from the past deserves surviving. To me, rotary phones deserve a sledge hammer, nothing else.

    1. Some places ooze nostalgia and highest-tech technology almost simultaneously. I was at a laundromat in Cambridge or Somerville, not far from M.I.T. but very long ago. An incapacitated or ill person handed me a piece of paper with a phone number. “Please call this, I need help,” she said. The nearby pay phone had a busted dial. Wiggling the hook I managed to raise some sort of phone company operator. I think I dialed 211. The operator said, “Light bulb.” I explained, and the operator reached the appropriate emergency services.

      This was long before 911 existed. Also, at that time MIT still had the “dorm line” phones that ran on a student-wired set of Strowger switches. Here’s a link to dorm line nostalgia:

  3. For the rotary line interface, look for a SLIC chip – subscriber line interface circuit. They will do everything needed. Or build a voltage doubler for a 12v supply’and switch with a reed relay. The bells will ring just fine on 24v.

    Ps I had no idea 911 wasn’t widely available in the US until mid seventies. We had it in the UK from late thirties! But then our Telco was a government run monopoly art that time, so mandating introduction was easy.

  4. Ah, the good old FeTAp Fernsprechtischapparat. Do not mistake it for a FeWAp, which would be a Fernsprechwandapparat.

    German 101:
    fern – distant
    sprechen – to talk
    Tisch – table
    Wand – wall
    Apparat – device

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