I recently found one of those old rotary dial telephones in my garage and amazingly it still is fully functional (I tested it by hooking it to the phone line). As I have no use for it as a telephone anymore, what I want to do is to make it ring on demand, using parts that I have on hand. The ringing as achieved by a small "hammer" being driven by a coil and knocking the bells. I measured the AC signal using a multi-meter when the ringing occurred and it read around 50V, which I guess is RMS, so peak voltage should be around 70V... at least that made it ring in my case.
At first, I tried using a transformer I had laying around but it had a ratio of around 23:1, but it made the AC voltage too low for the ringer to work (mains is 230V RMS at 50Hz).
Then, I found out about the capacitive voltage divider, but as I played a bit with it in Proteus I discovered that it seems to need large capacitors in order to be able to drive any reasonable load, like a light bulb. Also, I think the current drawn would be too much for continuous operation.
Lastly, I started designing an oscillator to generate the sine wave from a DC power source (new plan is to use a regular 5V wall plug). I found an example circuit that designs a single supply Wien bridge oscillator, and by adjusting the resistors and capacitors, I was able to generate a 2.5V 20Hz sine wave in Proteus. As physical parts, I plan the op-amp to be a TL-074, and the capacitors regular ceramics (I do not have a lot laying around unfortunately, so I am rather limited there). Next, I thought of adding the transformer that I have in the mix, in order to get the high voltage I need for the ringer. That should give me 2.5V * 23 around 60V peak AC, which hopefully will ring the bell. My remaining question, besides whether all this is a good idea or not, is how to handle the power drawn by the ring bell? I modified the circuit so that the output of the op-amp goes into the base of a TIP41, and then the collector and emitter are connected to the PSU, and the transformer, respectively. Should this be enough to drive the ring bell? Does the phone line really supply that big of a current, beside the high frequency? I played a bit with my telephone and saw that the coil of the ringer is hooked to a giant capacitor. When the line "rings", I can manually ring the phone by tapping the tip and ring wires to one end of the coil and the correct end of the capacitor, but it does not ring if I connect the coil directly. Is that because the line does not feed that much energy and the capacitor "buffers" it? Pardon me if I am wrong, I am just trying to learn, I am a bit confused here and would really appreciate some help to make things clear for me. A useful resource I used for learning about how the telephone line generally works is here. I'd really appreciate any idea on this matter, a different perspective on how to achieve this, I am trying to find a good working design before I prototype it on the breadboard or perfboard because I do not have an oscilloscope and debugging this without one I think would be pretty hard.
I am attaching a screenshot with my current schematic and simulation in Proteus. Yellow signal is generated sine wave before voltage rise, blue is the wave after the transformer, while green is a reference 5V peak 20Hz sine wave, just so that I make sure that the frequency of the generated wave is indeed 20Hz, which seems to be the case.
Thank you very much.