Phone ringer for stage use

dr pepper said:

Yes that sounds about right, 40v at 5ma from a 20:1 transformer would be 100ma primary current or thereabouts, only the voltage will not be the primary rated voltage, so the actual power will be around 5ma x 40v approx 200mw.
I suspect that 40v is the minimum for here in the Uk at least, I'm think the exchange puts out 75v ring voltage.

A thought on trannys, the thing to bear in mind is volt seconds, or volts x seconds, if a trans is 240v : 12v at 50hz, so if you wanted to run the thing at half the frequency then halfing the voltages would put you back in the cores operating region - I think.

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Yes, I'm thinking 40V minimum and willing to raise it if necessary. In this play there is some discussion as to whether to answer the phone so they need to be heard over it.

I don't quite get your second paragraph, can you explain a bit more please?

elfcurry said:

I suspected it wouldn't work on 25Hz but not sure what would happen. Also AnalogKid below isn't so sure it won't

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Actually, I'm pretty sure it will. It depends on the transformer and the circuit that is driving it, but an overrated transformer, such as one rated for 1 A but passing only 100 mA, should be fine.

ak

elfcurry said:

The phone for the current production doesn't have an electro-mechanical bell and I'm not going to mess about with its insides. My intention is to make something simple which any landline phone can be connected to, so it can be used for future productions too. I just need to provide the ring signal as though from the exchange, so the phone won't see any difference and the audience will hear a real phone ringing.

The IR remote is something I'd thought of but not because we're swamped with RF as this is quite a low-tech stage in a village hall.

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If you want to use the current phone and it does not have an old mechanical ringer with two domes then what does it sound like? Beeps? Buzzes?
I do not know if your audience knows that beeps or buzzes is a phone that is ringing, or a smoke alarm.

Since the dark ages, an old telephone was powered from DC when you talk or dial but the 90V/20Hz AC made the mechanical ringer swing its rapper back and forth to its two dome bells at its mechanical resonant frequency. Modern landline phones use a piezo beeper to beep when the phone receives the 90V/20Hz.

audioguru Non-electro-mechanical sounders have been common on landline phones for probably over 30 years. They respond to the ring signal and produce something I can only describe as 'warbling' electronic sound which varies depending on the manufacturer. One person I know still has the older type with real metal bells but there can't be many left.

(Where do you live? Are you phoning me from the past? )

Here in Canada I was renting an old fashioned Bell telephone that had a rotary dial and mechanical bell ringer for many years. Then in about 1980 I was given a wireless phone as a Christmas gift from work and its ringer warbled the two electronic frequencies. I bought additional phones with electronic ringers but did not pay extra for Touch-Tone so I dialed with rotary dial pulses for many years until a class action lawsuit prevented the Bell Telephone Company from charging extra anymore for touch Tone.

I guess today many people never heard the mechanical ring of an original phone.

elfcurry said:

One person I know still has the older type with real metal bells but there can't be many left.

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audioguru said:

I guess today many people never heard the mechanical ring of an original phone.

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On the contrary, here in the UK the conversion of .. ..


the typical 70's GPO telephone, for current use is a thriving industry since they are very popular as a 'must have' decorative accessory.

S

MM I have a 704 Gpo phone too, a green one.
To make them work on a Bt line you need a 3k3 resistor in series with the bell to limit its current.

EC the number of turns & core area are important factors in transformer design, if you run a trans at a lower frequency or higher voltage than its designed for you 'could' run into trouble.
If you drove 12v 50hz into the 12v winding of a 240v:12v 50hz transformer you'd get 240v 50hz out no trouble, but if you drove it with 12v 20hz you'd most likely saturate the core.
However if you drove the 24v side of a 240v:24v transformer with 12v 25hz you'd probably get away with it, your operating the trans at a lower freq than its designed, but your compensating that with a lower voltage.
Transformer design can get a little tricky.

dr pepper said:

MM I have a 704 Gpo phone too, a green one.
To make them work on a Bt line you need a 3k3 resistor in series with the bell to limit its current.

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Hi Dr P .. I don't have one here - I don't have a landline .. I was just pointing out that the notion of old hat equipment is far from the truth. The Retro look is alive and well. There is a retail unit not far from here that sell converted 'old style' telephones in various guises for staggering prices (£100 or so ) .. .. .. .

As for the transformer related stuff … way beyond my ken, as is the need to go there to achieve the required outcome.

S

Yes the price of the old 704 is ridiculous in some places, what folk will pay for what they think is trendy.
And that just bolsters the fact that such things are still popular, I like the fact the bell is nice & loud.
Some of the conversions are pretty bad too.

Not heard 'ken' for a while, I had a teacher that used to say 'I dunni ken'.

dr pepper said:

Not heard 'ken' for a while, I had a teacher that used to say 'I dunni ken'.

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Obviously Scottish then

search for "BT ring generator" Interesting: http://www.davidbuckley.name/dmxring/

That link under "local copy of schematic" points to this: http://www.davidbuckley.name/dmxring/ring1.gif

Then there is http://www.precisiovision.freeuk.com/ if you want to pay a few pounds.

Hello K I S S. Thanks so much for those links. I can't think why I didn't respond at the time but was busy around then just before Christmas.

The first one from David Buckley dmxring looks great and I'd love to be able to trigger it over DMX512 but at present I'm told it needs to be wireless controlled, which makes it more complicated. I'm not looking to buy a solution but I'll look at his description to see what I can learn.

I'm thinking that if I can demonstrate a decent-sounding ringing sound with a simple circuit with wires, then it'll be worth taking it further. If not, or there's more than a very small cost or modest effort with then this won't happen.

His second circuit looks nice and simple but I'd use a processor to generate the right frequency and control the double-ring timing.

Your last link is nice but well beyond any chance of getting paid for. Also it needs to be connected which I'm assuming rules it out.