Getting a modern phone to ring

[Scott M]

Argh!

Have promised to lend another local drama group my home brew phone ringer built from a PIC and a 4 transistor H-bridge driver circuit for a play this week. I've used this to good effect at my drama group to make various "proper" (ie bell & gong) phones ring over the years but have just found it won't run a modern piezo sounder type phone.

I've got two phones, one two wire and one three (Binatone dating back to the late 80s) and nothing happens apart from the LED flashing on the Binatone.

My circuit runs off 20v[1] and chucks out about 40v P-P on the output which I'd have thought enough.

Anyone any suggestions to get it going? I think their phone is a BT Viscount. Am I just going to have to find a decent 30+v PSU and use that?

[1] also tested it off a 26v supply I'd been planning to upgrade it to.

[Graham.]

If the actors voices are heard from loudspeakers rather than from their mouths, I can't see why the props need to speak for themselves ;-)

[gareth]

My guess is that you need a permanent 50V bias to power the electronics in the phone so that when you ring it, it is already expecting you.

Also, (But not covered in my beloved, "Atkinson's Telephony", nor it's predecessot, "Herbert and Proctor") the phone may be expecting a reversal of the 50V that will presage the forthcoming ringing.

[michael adams]

Position a mobile with an appropriately convincing ringtone behind the prop on the stage. Ring it from the wings with another mobile stopping when necessary.

michael adams

...

[Peter Andrews]

The BT spec (BT SIN 351) says that ringing voltage is between 40V and

100V a.c. The ringing voltage may be presented with or without a d.c. voltage bias. Your 40V is right on the minimum limit.

Peter

[alan_m]

Sometimes within a house with wired broadband and the modern phone(s) will not ring the trick is to use a cheap ADSl filter on every phone (at the phone end of the wires) to replicate the ringing circuit.

Scroll down to the end of

Note that they state not all cheap filters are correctly wired!

[spuorgelgoog]

Needing a permanent 50V bias to power the electronics is a possibility, at least for the Binatone.

The Viscount should be well-behaved and not require such.

Quite a lot of electronic phones will ring from DC applied to pins 3 and 5

- which can be tested by shorting the master socket capacitor and plugging them into a working phone line. It's easier to generate DC at 50 - 75 volts than a sub-mains frequency AC.

Owain

[Brian-Gaff]

Viscount? Is that the old sort with the clock that kept dying? Its interesting as some modern phones work on almost anything while others do not.

Could it be there is a dc offset on the line? Brian

[Brian-Gaff]

I seem to recall, as I eluded to in my last message, that you needed to have it superimposed onto a dc vvoltage for modern phones to actually power up enough to ring as the ring is often now controlled by the logic, not the ringing signal as such. This allows different rings etc, for different incoming numbers for those flash harrys who like that sort of thing. Brian

[Mike Tomlinson]

En el artículo , Scott M escribió:

If you're sending the ring current as pure AC with no DC offset, this can't be fed directly to the piezo sounder as it'd blow it apart. The phone contains circuitry to detect ring current and convert it into a low-level signal for the piezo sounder. For this work, the line needs to have DC on it as well.

Older phones with electromechanical bells feed the ringing voltage direct to the bell, which is why your ringer works.

[froggyfrog]

If there is a line reversal from the exchange then it is to prepare the apparatus for the receipt of calling line identification signaling before the ring, it is not part of the ring itself. The Viscount, being produced many years before CLI even appeared on BT's services list to customers doesn't decode calling line identification and will work with standard ringing as detailed in SIN 351.

BT SIN 227,242 cover calling line identification, 351 covers line technical characteristics

[charles]

but what happens if somebody else rings that mobile at another time.

[michael adams]

It's only switched on prior to the scene in question, and could even belong to a member of the cast. They could adjust the volume if necessary before and after each performance. If after all that, it goes off prematurely someone would need to lift the prop telephone receiver while surrepticiously switching the mobile off.

michael adams

...

[Dave Liquorice]

stopping

You set the mobile that is on set to ring only ring when a particular number calls it and to immediately reject all other calls.

The biggest snag will be the variable delay between pressing "call" and the on set phone ringing and pressing "hang up" and the onset phone stopping.

In a strong signal area the delay might be fairly short and consistent but in marginal coverage it can be several seconds particularly the "call" stage.

[Roger Mills]

The cast do a bit of rapid improvisation!

[charles]

and if the local service fails?

I once had to make a kettle boil on cue. That was quite an interesting project.

[Mike Barnes]

Make a recording of a phone ringing, and play it through a loudspeaker?

[michael adams]

Delays shouldn't be a problem.

The person in the wings only makes the call when he sees the actor is approaching the phone. The phone is only allowed to ring x number of times, after which the actor picks up the receiver.

The fine details could be worked out in rehearsal.

michael adams

...

[John Chance]

Have a look at how voip ATAs do it.

[charles]

but the audience appreciate it much more if the actor picks it up mid-ring and the ring stops.

As long as it doesn't restart when the actor puts the phone back on its rest.