Making phones ring on a closed circuit / intercom system

[sameshirt]

Does anyone have a diagram or an idea of a product that could be purchased to generate a ring on a closed circuit system?

I want to install a phone in the kitchen and one in the basement wired together.  I have seen the diagram with a 9v battery and a resistor to get the phones tot talk to each other. 

What I would like to have happen is:

When one phone is lifted the other phone rings
In the future it would be great to be able to add a third phone out in the barn.

this is all closed system, intercom type purpose with no outside connection.

Thanks!

Josh

[Owain]

Yes, you put a relay in series with each phone, such that when phone A is lifted the relay applies ringing voltage to phone B.

When phone B is lifted its relay disconnects ringing voltage.

And vice versa.

There was a circuit in August 1987 ? by N Cook-Abbott in Electronics and Wireless World. I'll scan it and post it up later (when the camera battery recharges)

[sameshirt]

That would be fantastic!  Then I would just need a transformer of some sort to supply the ring voltage.

Josh

[Owain]

the circuit includes an 18-0-18 V AC transformer. This assumes your phones will ring from AC mains frequency. In the UK that's 50 Hz; in the US 60 Hz might be too high.

[sameshirt]

I have read that 60hz freq is too high...

[Owain]

Circuit here as PDF.

Ignore the oscillator circuit and use the AC ringing.

EDIT: and here's the 10-line exchange using 22 relays

[Owain]

I built this (years ago) but mine never worked properly because I used 12V coil relays, and the off-hook voltage is lower and the relays didn't operate.

The circuit worked when I left the cover off the box and operated the relays by Mk. I finger control.

I'd be very interested in any feedback from anyone with experience of transmission or switching on the circuit, or anyone else who builds it.

[twocvbloke]

I'm just looking at the diagram there, and the oscillator circuit looks very similar to that on my Pye/TMC 1705 linesman phone's circuit diagram which is pasted on the lid (not 100% clear cos of the low lighting and my not very stable hands!!)...

It'd be interesting to build one though...

[AE_Collector]

A local company here in Vancouver Canada built a whole line of gizmo's for the phone industry back in the 70's and 80's. They were primarily things that to quite an extent became redundant once electronic PABX's took over. Things like manual and Automatic Intercoms primarily for multi line business phones. They were packaged nicely to mount on the wal of phone rooms and you fed power in and an output to each phone or a line key on a phone and they worked.

I see they are still in business but products have changed over the years.
http://www.dees.com/

The "DEES 125" Automatic Intercom was the highlite to me. When you went off hook on a line key of a Key Set it operated relays that rang buzzes and flashed line key lights on the other phone. It was designed to operate a 10 volt buzzer but you could feed the voltage that you wanted into it for ringing and it worked. I set up a whole bunch of them to use 90VAC ringing once though the bells had to be on a seperate pair from the talk path in the phone.

Terry

[Phonesrfun]

Here is an interesting circuit and instructions by Colin Chambers for using 2 or more 500 sets over 2 pair of wires to achieve not only intercom ringing, but coded ringing at that.  Some wires within the 500 need to be moved, but this is a non-destructive rewire that can be easily changed back.  I have not built the circuit, but everything else of Colin's that I have made works.

See the attached pdf file at the bottom of this post.

[MDK]

Seems pretty hi-tech. Could you connect a battery (or DC power supply) and a crank magneto do the same thing?

[Phonesrfun]

Seems pretty hi-tech. Could you connect a battery (or DC power supply) and a crank magneto do the same thing?

Of course.

However, you'd need a magneto at each end.  But in reality, 2 mags and a battery would work great for two phones.  When I was growing up, my neighbor and I had a line between our houses and we had a couple of mags and regular 500 phones and a single 6-volt lantern battery.  It never failed.

The more extensions, the more magnetos are needed since each has to have its own way of generating ringing current.

Don't forget that any pair of local battery phones such as the old wood magneto crank phones are made just for that kind of application.

The circuits approach is kind of a "project" approach and a learning experience.

[MDK]

I assumed a magneto would be needed at each extension. I may try this myself with one magneto. I rarely need to call in to the house, but often the wife needs to call the man cave in emergencies, like... we're out of flour, or the cat needs water.

[G-Man]

If you want a ready-made solution instead of a home-brew one, then ringdown units are available from a number of manufacturers. While not always cheap when purchased new, you can occasionally find one reasonably priced on the  e-place:  http://tinyurl.com/7xvxk5l

They are self-contained and furnish both talk battery and ringing current when either of the handsets are removed.

[Owain]

I assumed a magneto would be needed at each extension.

You need a magneto or an AC source at each extension to rung the other.

You might be able to get a away with a DPDT centre off switch, applying forward and reverse DC pulses to the line, wiggle it fast enough and should approximate AC enough to get the bell tinkling.

It just needs to be AC enough to get through the condenser if you're using central battery. Local battery often omit the condenser as there is no quiescent DC on the line.

Or use a local  wall-wart with AC output adjacent to each phone, decidedly not in the spirit of things but a probably cheaper source of AC than a magneto.