Sending ringing current toward a CO on a dial tone trunk [Telecom]

A common problem in magneto systems was that subscribers forgot to ring off. That's a reason telephones have hookswitches; so that when the subscriber is finished with the call and "hangs up the phone", the action cuts out the circuit.

Maybe I'm missing something here, but if the system is in place and in use, what kind of interface does it already have to a central office? Are these new owners or existing owners?

At this point I'd like to respectfully interject an observation: I personally am big on "old time" stuff, but almost everyone else are not. To actually use a handcrank phone or even a dial phone might be interesting--once--but not after that. I can't help but suspect a guest might enjoy making _one_ call on a crank phone, but after that find it rather tedious.

I am not a technician, but I'd like to offer some general observations. (I am curious as to what the technical people will say.)

Based on a special tariff announcements, many old legacy wiring arrangements are supported--for a price. That price probably is higher, or much higher, than to use modern technology.

As an example, unattended railway stations need an emergency phone in case a passenger needs help. It is often cheaper for the carrier to simply pay the phoneco provide a standard pay phone rather than pay for a dedicated 'lift receiver' line.

Certain old arrangements are no longer supported in some areas, such as party lines or 20/60 milliAmp teletype service.

What is supported varies by individual C.O.

I would suggest containing the Business Office Professional-Services representative at the phoneco serving the hotel.

I can't help but suspect the phone company will not be interested in supported this oddball arrangement; but if they were, it would be quite pricey for a custom engineered arrangement.

In situations like this often a 'black box' interface that takes the standard telco CO interface on one end and the magneto interface on the other might work out. Obviously the hotel operator will need a dial capability, be it pulse or Touch Tone.

But I would question the need for the hotel operator to require magneto signalling to the C.O. Switchboards did handle both types of signalling and acted as an interface between the two systems. I don't think there's a reason that the switchboard couldn't have standard PBX trunk circuits and magneto circuits for the extensions, though the cord circuits may need modification.

And that's why manual board operators would "listen in" on "active" patches every now and then. Plus, as "automatic" CO switching became available, manual boards would have appearances of modern "common battery" trunks at board positions, with the "adapter circuitry" (including a dial) to go between the "new" CO line and the old magneto circuit(s). Are you sure this board doesn't already have such circuits (equipment) in it?

*wonders if they also use "charming" outhouses too...*

Plus, what happens when one of the guests tries to use the cranky old phones to call a modern system to, say, hear their voice messages? "Press 1 to play" isn't much use when there's no 1 to press...

***** Moderator's Note *****

The PBX in question definitely does _NOT_ have any interface capability. I'm told it's a military-surplus model, strictly local battery/local magneto. I asked if it's the same as the one Gary Burghoff used in "M*A*S*H", but it turns out to be closer to Bebe Daniels in "Chickie".

I don't think they have outhouses: I think the owners at this place probably want their guests to remember how nice things looked in old movies that showed crank telephones in rural settings. As we all know, nobody ever uses a toilet in the movies ... ;-)

If the guests are interested in checking their voice mail, there are regular TouchTone phones within walking distance, but there's probably little demand for them: I'm told that the guests go to this place _because_ it's free of the distractions of modern life.

Bill Horne

Depends what you consider 'a lot'

Interfacing a common-battery system to a local one _is_ going to take a fair amount of 'glue' hardware.

I'd probably look at using an Asterisk PBX, with FXS cards to connect to the PSTN, and E&M cards as part of the interface to the magneto PBX.

Would need some (relatively) minimal additional outboard hardware to: 1) detect the magneto signal, and provide an 'interrupt' to a custom line handler module. 2) provide isolation/transformer coupling of the divergent battery sources. 3) open/close the talk path when indicated.

Items (1) & (3) could be probably handled by something like an AWC "GP-3" I/O board ().

Item (2) could be handled with opto-isolators, or maybe a 1:1 transformer with a series cap. on each side. May have to add amplification and/or attenuation, to get the audio levels right.

Can probably be done for something in the low four-figure range, all in.

wrote:

'Fair amount' is just that, not an overwhelming task and actually well documented in the 'practices' if you have them or can find them online or elsewhere.

I used to detect ring (interfaces I made as a kid) using a diode charge pump feeding a darlington or fet and comparing with a threshold level.

A pretty standard task; I have a Tellabs box that I often use (with various cards) for experiments such as these.

I trust that the operator of the cord board will do this? Otherwise one could set up some fancy voice recognition and automation robot for this ;)

Interesting how I have found different interpretations of the "figures" expression over the years; frequently folks use that expression to refer to the number of zeros after a significant digit in a monetary value; do you mean in the $10k range? IMHO, with surplus hardware (e.g. old PC, the contents of most decent 'junk boxes', and donated time), one could do this for the cost of pizza and a movie.

Michael

So, at present, the rooms have no ability to be connected to the outside world.

The way you describe the place, its owners, and its patrons, maybe that's the way it should be left. Presumably the resort offices have normal lines to the real world in case of emergency, take reservations, and conduct business; and guests have their own cellphones.

(Otherwise, I'm confused as to what needs to be done and why.)

The cord-board described didn't have any interfaces for 'common battery' circuits from a C.O. You've gotta play some games interfacing the local battery/magneto line from the PBX the E&M board in the Asterisk "C.O." you can build all the requisite logic in hardware, or run a 'magneto detector' that sends a signal to the PC, and the PC goes through the gyrations needed to take the E&M link 'off hook'. This can be done with a couple of relays, under software control, rather than using 'hard-wired' logic.

'4 figures' means greater than $999 and less than $10,000 -- i.e. _four_ figures ($1000-9999). The 'number of zeroes' approach gives the _upper_bound_ for the range -- good for "worst-case" estimating, but significantly over- states the 'typical' amount.

You're clearly not an accountant, are you?

I was making the assumption of a 'business' transaction, since the job _is_ for a business. That means anything used goes at 'market' rates -- can't "afford" to deploy an 'old PC', when you look at the price of a _new_ one that includes a *warranty*. Parts that come 'out of the junk box' are still 'inventory', and have to be replaced (at *market* prices). And the guy coding the custom software gets paid a 'professional' rate.

Yeah, a hobbiest -- doing it solely for his own personal use/enjoyment -- could do it for a lot less, given a reasonably-stocked junk box.

Egad! I was wrong.

Thinking a bit more about the problem, I realize that it is _much_ simpler than I originally thought, or what the OP proposed.

It is simply -not- reasonable to do a 'direct' connection between the PSTN and the magneto board in question.

*HOWEVER* one -can-, relatively trivially, provide interconnect *_functionality_ between the two systems, as follows:

Take a regular PSTN tail-loop, with a standard CPE set. Add a 'ham-radio type' manual phone-patch to the line. Connect the audio in/out from -that- to a line on the switchboard. (this may need amps/attenuation, but is simple, inexpensive, audio components)

Since the PBX _operator_ is always involved in call handling, _they_ provide all the necessary glue 'logic' using the carbon-based computing system between their ears.

For an outgoing call to the PSTN, the switchboard customer 'rings' the operator, and gives the desired number. The operator picks up the telco set, and makes the call. When the called party answers, they (a) switch the phone patch on, and (b) plug the 'calling' extension into the extension that connects to the phone patch.

For an incoming call _from_ the PSTN, the operator answers the PSTN set, determines who the call is for, then, on the PBX, 'rings' the appropriate extension, and when somebody answers, cross-plugs to the phone patch extension and switches the phone patch on.

For bonus points, one adds a detector on the line that -- only when the phone patch is switched _on_ -- listens for any of: dial tone, a crybaby, or the loud screech the PSTN C.O. uses to alert to an off-hook phone. (when detected, it alerts the operator -- that the call can be disconnected.)

Doesn't need the Asterisk, etc. at all.

***** Moderator's Note *****

There are a couple of kinks in this approach.

1. Ham radio phone patches are intended to a connect separate receiver and transmitter units to a phone line, so they contain hybrids and a balancing network, which wouldn't work for connecting two-wire circuits together.

1. I don't recall any energy absorption circuitry in the phone patches I've owned: I may be having a senior moment, but assuming not, a phone patch could be damaged by ringing voltage, and there's _way_ too much of that floating around in a "ringdown" system.

However, I like your idea of using off-the-shelf components. Ma Bell used to offer a "Direct Access Arrangement", which came attached to a

500/2500 set and was activated by pulling up one of the switch-hook posts. It was a two-wire interface, and contained circuitry to protect the network, and IIRC, it had a 210 jack that might connect directly to a switchboard cord.

Anyone remember what it was called or the USOC code(s). Any available used?

I've already traded emails with the Verizon Media Relations staff concerning the attitudes and rudeness of the representatives at the business office, and I'll run a story on the results in a couple of days. For now, suffice to say that the company's attitude could be best summarized as "Go Away Little Man, You Bother Me".

That sounds like a possibly workable idea. Have you any suggestions on how/where to _find_ such a piece of equipment?

Bill Horne Speaking strictly for myself

***** Moderator's Note *****

Robert Bonomi served as "Guest Moderator" for this post.

some USOC info here, page 4

lots of technical detail here

You are still dealing with Hell Atlantic. Dealing in other areas you can come up better.

The military did have interface devices to go between common battery field phone boards and the commercial telcos, but what you should know is that a field phone board is basically not useful for anything other than field phones and does not provide much in the way of signalling.

And maintaining local battery phones is a freaking nightmare. Who is going to check the battery status on the room phones every month?

It would be much easier just to use a common battery system... put a

48V supply into the back of the PBX with distribution resistors, so you have a number of intercom pairs... plug two phones into the intercom pair and they can talk.

Then the PBX seems to each one of the phones like it's the CO, and handing the call off to the CO is just a matter of the operator dialing the call, unplugging the room from a local intercom circuit, and plugging it into the call in progress. Since you're going to have to modify the hell out of the board to do any useful work anyway, you might as well.

--scott