Is the idea that you pick up the talky and speak into it directly?
Does the microphone inside the Type37 talky work or will you need to replace it?
What kind of audio are you collecting? (Vocal Memos? Ambient room noise?)
Here is the big one… how will you store the data? How much audio does it need to store? Hours? Days? (I imagine the easiest is writing the recording to an SD card which can be fished out later).
Another challenge is discerning if the talky is picked up.
I have a few ideas, but to recommend something I’d love to see a picture of your particular unit.
Power… does the phone have power already? If so what is the volts and amps of the source?
Fun. Was there something particular you feel stuck on?
Hi Nareah
If you plan on recording phone calls I would be very careful.
The authorities come down pretty hard when calls are recorded without spoken warning or illegally. I think any sort of private recording would be illegal.
Cheers Bob
@Robert93820
Thanks for your input! Just to clarify, this won’t be used for telephone calls. The idea is purely for entertainment at parties or weddings, where guests can lift the phone and record their wishes for the event hosts. It’s meant to be a fun, interactive attraction using the antique phone shell. Your suggestions are still valuable, though! Thanks again!
The phone has no power, as it originally worked only with signals, so we’ll be incorporating all new tech inside to power the project. I’ll definitely share some pictures of the unit to give you a better idea.
For the recording, it’s just a few seconds of audio (like a vocal memo), as it’s primarily for parties where guests can record their wishes. A small SD card should be sufficient for storing these short messages. I’m planning to use a small battery inside the box to power the setup, which could include something like a Raspberry Pi or Arduino with a simple microphone and trigger system.
The challenge is figuring out how to detect when the receiver (talky) is picked up, but I’m open to your ideas! The main goal is to keep the outer shell intact for its antique look, while updating the internals with modern technology to capture and store short recordings. Any guidance on components or setup ideas would be really appreciated!
If the talky is slightly reflective to light (i.e. shiny) then I think I’d use this to detect if it’s hooked.
I’m imagining this on the side wall of the box looking at where the talky would rest so that if it’s not there it can notice and tell the micro-controller to start recording.
Is the idea to the put the microphone inside the talky itself or are you planning on putting the microphone inside the box and just record the ambient environment?
Here are the images of the phone I have. I’m not concerned about anything inside except for the small trigger you see. When the phone is lifted, it should activate and play a short pre-recorded message, such as “Please record your message.” Then it should record the audio and store it until the phone is placed back on the hook.
OH YEAH! How stunning.
I recon this MEMS micrphone riiiiight at that arrow will be perfect.
Getting audio out into the speaker might be a little harder but worth it for sure.
What is your budget for this?
How much engineering and software skills do you have coming into this?
That looks like it might be a schematic.
May we please have a close up of that?
@Robert93820 this looks like a lever activated mechanical switch to me? Do you recognize it?
Is there any way Naresh could use that instead of a IR sensor?
Yes, it is as you suggest. I can’t remember how all this worked back in the day. All quite ingenious actually. The off hook was signalled back to the exchange by a contact closure I think which put a short somewhere. The whole thing would be powered by the 48V on the phone line. The ring tone was something like 100V+ at 17Hz to clang the bell. I know you can get quite a “bite” from it.The microphone audio (Carbon Mike, that is what the 48V was for) was arranged to provide a “side tone” for the ear piece so you could hear a little of what you were saying in your ear. This made everything sound more natural instead of the effect of talking into nothing with no feed back. Similar to the “Foldback” speakers or ear pieces for a live stage performance. I think that is a function of that transformer.
I think this contact could be utilised to signal an Arduino or whatever.
As the reception was AC for audio the ear piece was a fine steel shim biased with a magnet. If you did not have the magnet the audio frequency would be effectively doubled and sounded like Donald Duck. Have a think about how this would happen. Will keep the old mind ticking over for a bit, unless of course you already know. Anyway for this purpose and be compatible with the modern era a small speaker would replace the ear “receiver”.
The same applies for the microphone. Carbon mikes really are a thing of bygone days.
Cheers Bob
Super cool device! The engineering behind these original phones (and the network behind them) really is ingenious.
I was going to mention the built-in receiver detection as Bob did, it is built for higher voltages but could likely be adapted to work with logic-sized voltages, with some effort.
For a visual explanation of how this all worked, I would recommend watching from about 2:25 - 3:00 on a recent video by youtuber Veritasium.
Try and look past the clickbaity thumbnail, hard to escape it nowadays. The small section I mentioned above is all you really need to understand the Type 37. It may not work exactly the same, but should give you a good idea.
P.S. As Pix mentioned, I’d love to see a close-up of the schematic, if possible!
I think for this application an amplifier and small speaker would be appropriate. I think the more modern phone actually has a small speaker. The metal shim and biasing magnet is pretty archaic.
By the way. Has anyone worked out why these old systems would frequency double without this biasing magnet. Think about it.
All up, you would have to praise the people who invented and built some of these devices. In their day they would not be far short of genius. Even that telephone is really clever and a credit to them.
Cheers Bob
Skimmed to the end, so I may be repeating suggestions here…
Why not use the actual switch the phone uses to know when it’s picked up? Just piggyback a couple of wires off it and hey presto.
And I dunno about impedance etc, but I’d say you should find a way to use the original microphone and speaker; that would preserve the old tinny sound which people associate with these things. That would be a high priority for me with this project, worth any extra faff like extra circuitry to accommodate it.
Seems to be enough spare room inside to accommodate a lipo and your circuitry while leaving the original stuff in there. If you wanted to get really fancy it might even be possible to have it charge from plugging it into a phone socket…
Hi All
I don’t know how many people here are up with how a carbon microphone works. It was easy in the day but you need the exchange 48V or similar for it to work. With the modern trend for 3.3V and anything above 5V being considered “high voltage” I think the practicalities of getting the original to work could be way too difficult.
I think the same could be said for the earpiece. The easy way out would be a small speaker or if you can get some sort of fidelity even a piezo device.
Of course the original bits COULD be made to work. This would entail some research to find out exactly how this phone works remembering you don’t have a phone line to deal with. The line could be simulated with a couple of resistors but the termination at the exchange end simulation could be tricky.
There undoubtedly is a wealth of information on line or you might get lucky and find an old PMG (now Telstra) technician (not Me, Although I had dealings with PMG not down to that level) with a good enough memory to help out.
Cheers Bob
These old schematics don’t look like the modern variety do they.
I have no idea what “induction coil No 14” is. might be a transformer or just 2 chokes. looking at the real thing (which we can’t do) might give a clue.
The gizmo at the bottom is a capacitor, Marked on another schematic as “2MF”. I am sure they mean 2mF (millifarad) as 2 Mega Farad would be ENORMOUS even by todays standards. I believe it couples the 17Hz ring signal to the “magnetic bell”.
The other schematic
Thank you, everyone, for sharing your thoughts! I’m an IT technician but not an expert in board-level repairs. I can handle a bit of soldering but have mostly chosen parts with pins to keep it manageable. Here’s the list of parts I’m using, along with a few spares, and I’m using all new components while repurposing the phone’s external case.
Please let me know if I’m missing anything, and I’ll update here once the project is completed.