[Yaymukund] made an interesting observation. Old-style rotary phones were made to last and made for service. Why? Because you didn’t own them, the phone company did. There was no advantage for them for you to need a service call or a new phone. Of course, many of these old phones are still hanging around like the GPO 746 that appears in the post.
What do you do with an old rotary phone? In this case, you make it play a random tune whenever someone picks up the handset. As you might expect, you don’t need much of the original phone to do this. In particular, you need the handset receiver and the switch hook. We’d have liked to read the dial to select a tune, but perhaps that could be in version two.
All the components wire back to a D92732 circuit board. Finding the right wires was a bit finicky, but eventually, a Teensy, a battery pack, and an audio breakout board were in place. The rest is mostly trivial.
[Yaymukund] spent about £300, but over half of that was on tools most Hackaday readers will already have. The phone itself was £65. You can use these phones as a basis for many projects. Even if you want to go mobile.
The phone itself was £65
That sounds…expensive.
It’s an antique.
That’s the “need it but don’t have it” price. If you didn’t need a rotary phone, no doubt you’d stumble across someone selling a pallet of them for $20. But since you do need one, $50+ is the best price you’ll find. Every damn time.
“Don’t lowball me, I know what I got!”
It is. You can usually find them far cheaper Unless you are looking for a specific colour/aesthetic
It really is, the one I’m converting to VoIP was £10
Do you like our owl?
I feel that using a SLIC module would have been a better way to preserve the phone in its original state and also make the phone ring.
This is a pretty good example:
https://hackaday.io/project/190181-the-phone-friend/log/222340-all-aboard
I have a Chicago Telephone Supply Co. wall-mounted telephone from around 1906. Debugging and repairing 120+ year old circuitry has been surprisingly fun. Cotton-wrapped wires, the “cable management” of which constitutes embedding them into grooves the wooden case using candle-wax as a fixing/insulating medium; a hand-crank to summon the exchange; and a “lightning isolator” to prevent current surges (I suppose the Carrington Event was still within living memory when this phone was designed…).
In the 80s when I was in high school I bought a touch tone phone when they first became available for the public to purchase (before you could only rent them with your phone service). I got a bright red one, and I think it still had a sticker on the bottom that said property of Bell Telephone.
They had a pretty simple and ingenious design. I started messing around with its insides when I decided it needed to have a switch to disable the ringer (not just reduce it’s volume by moving the little wheel that changed the bells distance from the hammer).
I used a little relay from Radio Shack that, when a switch I installed on the side was thrown, would use the current from the ringing to trigger a red light I mounted on the side, powered by a nine volt battery. The light would pulse at the same frequency the ring would normally happen.
The next switch and relay I installed put the phone into “auto answer” mode. The first little pulse of the ringing would trigger the relay to connect the wires that put the phone “off the hook,” and answered (even though the handset was still on the hook). The power from the battery then kept the relay engaged, keeping the phone “off the hook,” and the red light would turn on solid. The result of this is when someone called they would not hear it ring at all, they were just immediately connected (and could hear anything going on in the room through the mouthpiece). The handset could then be picked up to start talking.
Another switch on the side, and a variation of the auto answer, was once the call was immediately connected it would trigger a tape recorder that played to the person calling (a kind of half an answering machine this was). I later experimented with the voltage threshold that would indicate to the phone company that the phone was off the hook and answered. I found I could play music at just below this threshold straight into the twisted pair. Amazingly, if someone called, they could hear the music playing faintly under the ringing. This could theoretically be used to pass messages to someone without actually completing a call.
The next switch used a relay as a spy-detector. It was dialed in voltage-wise so that if an extension on the same line was picked up, the resulting small drop in current would trigger the red light to go on (this was my private line, and there was no extension for someone to pickup, this was just a fun exercise).
Later, in college, I happened to have a motion detector from Radio Shack, and decided to mount it high on the wall so you could turn on the stereo and reel-to-reel to play music by raising your hand in the air (a much larger relay was used here). Then, the phone was wired to this setup so that if the handset was lifted off the hook, the power would be cut to the stereo, turning the music off immediately (you know, ’cause you were going to talk on the phone). My friend McKenzie was so tall that when he walked into the room the music would turn on.
There was Phoneco
https://boingboing.net/2023/11/12/tens-of-thousands-of-old-phones-linger-in-vintage-sellers-inventory.html
Well if you can plug it into a landline jack, it should still work
Atleast pulse dialing still works on the phone lines here
I know because I could switch my cordless phone to pulse dial in the settings and the calls still went through….
Maybe need isolation or level shifting depending how the landline phone line operate nowadays
Different is that instead of the phone making dtmf buzzing when it dials
It’s just farts a bunch of clicking noises like the rotary phone dial
With all the digital stuff on the landline its not difficult to digitally decode dtmf, and simply use a pulse counter out of a basically a shift register
Maybe make one that lets you talk to a voice-LLM.
That works both as a novelty gadget and as a nostalgia thing for older people. if they are nostalgic for such.