Does that ring a bell?

I am trying to convert an old rotary phone into a timer used by my kids. Most of the project is already done and working - the timer can be set with the rotary dial, it fires off correctly etc. I have also set it up for battery operation - the Arduino is turned on if the piece is taken off the hook.

What I have problem with are the bells - I hoped that I could use the original ringing mechanism. However, I realize that it was designed for circuits with more voltage - obviously I would like to avoid that for a DIY batter device operated by kids. For now I have just connected the electromagnet to two pins and I am switching the signals - the hammer oscillates, but it does not have enough force to strike the bells to produce decent sound.

I have thought of a 9V battery and relays, but then I am not sure how to reverse the current. I have also considered a servo with a metal piece, but I do not know whether it will be strong enough to produce sound...

Any other ideas?

Does that ring a bell? *

48V at least, at the exchange, to ring the bell.

* Little ASCII gag there

Some of the big old fire alarm bells that used to be on the side of factories, used to have an electric motor inside the bell dome and the striker, spring mounted, would rotate on the shaft and strike the edge of the bell.

Just a thought.
Tom… :slight_smile:

Use an inverter to get the voltage you need to drive the original bell. Back in the 60's I did lighting and sound for theater and I made a circuit to ring a phone on stage. I used a multivibrator driving a transformer backwards to get a high voltage.

The best solution is probably to simulate a ringer with some kind of sound recorder chip, a little amplifier chip, and a speaker. Or, a quick search turned-up [u]this[/u].

If this is an old style mechanical bell, you might be able to use a solenoid as a striker (switching it on & off). That would probably be a 12V solenoid.

Or, you could re-wind the existing coils. But, that would be trial-and-error for the number of turns, wire gauge, and current required.

My memory could be wrong, but I thought ringing voltage was 90V at 20Hz (here in the U.S.)

My memory could be wrong, but I thought ringing voltage was 90V at 20Hz (here in the U.S.)

That is what I've read. Here is a ring generator circuit with those specs:

Thank you for the discussion, it is quite helpful.

While I understand that specification for the phone circuits calls for specific voltages, it seems that in case of this particular phone the voltage needed to produce a decent sound is significantly lower. I am able to ring a single bell (there are two) with 9V applied to the coil.

How about a small low voltage model motor that has a off centre weight attached to the end shaft. Then, it can simply bang against the bells until you go deaf.

The code will be simply be motor on or motor off.

Edit: oh, just like Tom suggested earlier, oops :D


Try a battery that isn’t one of those crapola 9v ones. They are terrible, truly awful current handling. If it rings one, it’d be able to ring two if it could take the current. Use 6 or 8 AAs, or generate it from the main supply via a dcdc converter

That is what I’ve read. Here is a ring generator circuit with those specs:

Here, in the UK, ringing voltage is 75V AC at 25Hz.

Or play an MP3 sound file of the bell

I agree, it is not the same but at least safe for kids

Yes Rob, great idea, maybe something like Tubular Bells performed at Dom Tower Utrecht I've lost count of the times I have run up an down the narrow stairway that leads to the roof of the Dom tower, past the carillon itself. A few years prior to this clip I did the video link from the carillon players point, carrying and setting up the microwave link equipment. I can say, it was loud, I should have taken ear muffs.

But can you image, Jabberwock installing a good size sub woofer and playing Tubular Bells each time the phone rings. A decent battery pack will be needed :)


off topic @rockwally - drone recording of the Dom Tower Utrecht - -