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Old 11th Jun 2017, 2:22 pm   #1
boombox
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Default House intercom situation (again)

So with massive thanks to AndiiT, I'm nearly there with my house intercom setup for this tall but narrow house we're moving into.

At the moment it looks like I'll be using a Linksys VoIP switch wired up to two GPO rotary dial phones. I've got to iron out some audibility problems but it works so far that if you lift the handset on one phone the other rings and visa versa. Speech works well in one direction but doesn't in the other. But I think that will just turn out to be wiring in the phone itself and AndiiT has given me some guidance on sorting that out. Just need to get round to debugging it.

In the meantime my wife has taken a bit of a shine to one of these old GPO phones that I'd earmarked for the intercom project. She wants to use it as a house phone connected to the PSTN.

So that got me thinking. Is there any way:-

- Can a cheap older PBX be configured that you DON'T need to dial '9' for an outside line and instead it assumes you want to dial outside unless you tell it (somehow?) you want to dial internally? The reason I'm wondering about this is I know what a faff it would be if guests/babysitters/family members all had to get into the hang of dialling '9' before placing calls. Not gonna happen.
or

- Could I rig up a toggle switch that would change what the GPO phone does? As in, it would mostly be hooked up to the PSTN but at the flick of the switch it could be used to call upstairs rather than to an outside line?

- Or is there an option 'C' I'm not thinking of?

many thanks!
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Old 11th Jun 2017, 2:59 pm   #2
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Default Re: House intercom situation (again)

Quote:
Originally Posted by boombox View Post
Can a cheap older PBX be configured that you DON'T need to dial '9' for an outside line and instead it assumes you want to dial outside unless you tell it (somehow?) you want to dial internally? The reason I'm wondering about this is I know what a faff it would be if guests/babysitters/family members all had to get into the hang of dialling '9' before placing calls. Not gonna happen.
All the PABXes with which I have had dealings require an access digit to connect to an external line - and most use "0" to access the operator/master telephone.

If your PABX defaulted to connecting to an external line, how would you then tell it that you wanted to make an internal call?

IF "0" could be configured as the access code and the PABX could then be persuaded to send that digit on, I suppose it would be feasible. Of course, If you had that arrangement, you would have to include an exchange code, even for numbers on the same local exchange.

Is it not easier to leave instructions to dial "9" for an outside line, or simply have a telephone directly connected in parallel with the PABX for such use.

Personally, I like the idea that casual use of my BT line can be discouraged by the need to start with an access code. Not that the situation actually arose, but I had an action plan for if my then telephone-button-happy toddler great-nephew was staying, I would even have disabled "9" as the access code for the external line connected to BT, as each line has an individual two-digit access code as well.

Methinks the greater "faff" for your above-mentioned users would be having a rotary dial to use rather than buttons. A few years ago I was showing a teenager my vintage telephones and suggested that she dialled a number on the 'phone in front of her to speak to me on another 'phone, to which the response was "how do I do that?" She had never encountered a rotary dial before!

Your second option of a manual switch is certainly a possibility - but it would then require remembering to return the 'phone to direct connection after making the internal call.
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Last edited by Dave Moll; 11th Jun 2017 at 3:08 pm. Reason: Added comment about option "B"
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Old 11th Jun 2017, 3:05 pm   #3
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Default Re: House intercom situation (again)

One of those adapters that Mercury or other alternative service providers used to supply may be reprogrammable. They dialled an access number for their service, then added the number you were dialling. Whether they worked on LD or could be persuaded to just dial one digit I don't know, but I'm sure someone on here will!
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Old 11th Jun 2017, 7:51 pm   #4
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Default Re: House intercom situation (again)

Quote:
Originally Posted by boombox View Post
....Can a cheap older PBX be configured that you DON'T need to dial '9' for an outside line...
Hi, the only PBX I have seen which allows a "direct access" option to an exchange line is the Tiptel range which are not easily available these days, I think Dave Moll queried how you would then call an extention in this case - it's done by dialing * before the extension number required. Of course you need touch tone phones to do this and your 700 series phones won't have this facility.

Quote:
Originally Posted by boombox View Post
...Could I rig up a toggle switch...
Obtain a press button assembly and a pair of switch no.23A's (locking) for your 746, if it is a 746, then fit and wire them so that one position of the switch connects the phone to your intercom line and the other connects to the exchange line, you could use an external double pole change over switch or a switch 2A to do the same thing but in the case of those they would have to be mounted external to the phone, or is using an "off the shelf" switch some cosmetic modification to the phone case would be required if you wanted to make it an integral part of the phone.

Feel free to PM me again if you want further details

Regards

Andrew
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Old 11th Jun 2017, 9:31 pm   #5
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Default Re: House intercom situation (again)

Go for Option C:-

Plan 107?

Option D:-

2 station cordless phone with intercom facility?

Option E:-

Shout!
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Old 11th Jun 2017, 9:36 pm   #6
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Default Re: House intercom situation (again)

Without wanting to sound too much like a broken record, a scrap PC with the free Asterisk software and a hardware card providing FXS (phone) and FXO (exchange line) ports will let you do all manner of funky stuff; including dialling a number as soon as you pick up a handset, or recognising short codes and calling an internal or external number. (My own setup responds to 4-digit numbers as being numbers in my parents' village, long-since prefixed to make them up to 6 digits; 6-digit numbers as my home city; 7-digit numbers as being up the wrong end of the '52; and 3-digit numbers as being Work extensions. Anything longer is treated as a number with an STD or IDD code.) Oh, yeah, baby, telephony is addictive .....
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Old 11th Jun 2017, 10:17 pm   #7
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Default Re: House intercom situation (again)

Quote:
Originally Posted by AC/HL View Post
One of those adapters that Mercury or other alternative service providers used to supply may be reprogrammable. They dialled an access number for their service, then added the number you were dialling. Whether they worked on LD or could be persuaded to just dial one digit I don't know, but I'm sure someone on here will!
There were two options on these ( for Mercury, at least).
One dialled 131 followed by a code ( something like 7/8 digits), the other dialled 132 and Mercury etc looked for the registered number to be seen. ( Caller ID).
From what I remember ( don't forget that this was 20+ years ago), 131 could be in either LD or DTMF, BUT after that all other digits into Mercury had to be in DTMF.

I can't remember what system was used on 132.
But I do remember one other system I used ,provided by an energy company, where a home "smartbox" converted / prefixed non local numbers with the code the company used. to allow the access code to be sent to line.
Personally for a simple house intercom, I'd look at something like a Plan 7/5 or a 107/105 .
And if you want phones to ring- why not look into ringer converters. Used on BT PABX to convert ringing to operate an external bell .
Oh- yes telephony is so addictive.
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Old 12th Jun 2017, 12:05 am   #8
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Default Re: House intercom situation (again)

How about a phone with a 'party line' switch on the cradle?

you could use the phone as an intercom, but when you wanted an outside line you just press the button, which IIRC just shorts to earth and retrieves the dialing tone.
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Old 12th Jun 2017, 6:54 am   #9
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Default Re: House intercom situation (again)

Wouldn't you need some extra hardware to emulate the equipment that would have been installed at the exchange to handle "shared service"?
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Old 12th Jun 2017, 11:50 am   #10
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Default Re: House intercom situation (again)

Quote:
Originally Posted by boombox View Post
At the moment it looks like I'll be using a Linksys VoIP switch wired up to two GPO rotary dial phones.
- Can a cheap older PBX be configured that you DON'T need to dial '9' for an outside line and instead it assumes you want to dial outside unless you tell it (somehow?) you want to dial internally?
Does the Linksys you are using have FXO (foreign exchange office) or PSTN ports as well as FXS (foreign exchange station or phone) sockets? Many small VoIP TAs do have a phone line pass-through which you could use for the BT line.

Then the TA would handle outdialling on the BT line or VoIP intercom-intercom calls.

Panasonic KX-TA PABX have a variety of 'hot line dialling' and 'prime line' settings so might be programmable to autodial 9 after x seconds if an intercom number isn't dialled. They also have call barring so your babysitter could dial your mobile number with a speed dial code, but can't phone the boyfriend in Australia etc.

The VoIP TA may also have call barring/routing options to put calls out over the PSTN or through a VoIP account.

There are some safety implications if your babysitter etc needs to dial 999 and isn't familiar with the phone system.
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Old 12th Jun 2017, 12:37 pm   #11
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Default Re: House intercom situation (again)

Quote:
Originally Posted by Dave Moll View Post
Wouldn't you need some extra hardware to emulate the equipment that would have been installed at the exchange to handle "shared service"?
Presumably the 2 core (instead of 2x2 core for two lines) brings from the exchange one 'half' of each of the two lines on the shared service and then each is connected to a common return which when earthed causes one number of the two to dominate......oh well maybe something like that, not sure
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Old 12th Jun 2017, 2:08 pm   #12
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Default Re: House intercom situation (again)

I'm not familiar with the details of shared service, but my understanding is that momentary earthing of one leg or the other tells equipment at the exchange which party is initiating a call, thus indicating which subscriber to meter. The line is then connected between the A and B legs, with earth no longer playing a part until the line is cleared down. To alert a party to an incoming call, assuming neither has a call in progress, ringing current is sent between the leg assigned to that party and earth. Again, once the party answers the connection is made as above. If the other party picks up while the call is in progress, they would effectively be connected in parallel and would be able to hear the call in progress - and to intervene. The etiquette being that the handset is then replaced unless the second party wishes to claim priority, such as needing to make an emergency call.

What I understand to be needed here is somewhat different, in that the telephone is to behave in a normal manner to connect to the telephone network by default, but having some way to swap to a connection to the PABX, either by a special input (such as the "*" mentioned earlier - though not available on a rotary dial) or a physical switch which remains in effect until the internal call is cleared down. The 'phone then reverts to its default direct network connection.
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Old 12th Jun 2017, 2:45 pm   #13
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Default Re: House intercom situation (again)

Hi again, the OP's requirement isn't a particularly complicated one although some of the responses do appear to be somewhat complex.

The suggestion of using Asterisk is good one although might be a bit of "overkill" where there is just a requirement for two phones and only one of which requires exchange line access (as I understood the initial request)

Getting back on to the subject of physical switching, further to my original suggestion of a pair of 23A switches etc. another option could be a pair of switch 5A-3's (non locking) and a latch assembly of the type used in the 740 type phone where the switches are wired to change to exchange line when the auxiliary button is depressed and then remain latched until the telephone handset is restored, the caveat with that (or the other method I mentioned) would be that the additional extension phone might ring until the "exchange line" button is depressed.

I might have to visit my own "experimenters corner" and see what can be done.....

Regards

Andrew
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Old 13th Jun 2017, 8:28 am   #14
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Default Re: House intercom situation (again)

A single-pole single-throw momentary switch can be connected to the telephone and trigger an impulse relay that will change the phone between TA and BT lines.

The impulse relay will retain its setting until retriggered.

Getting the phone to return to a 'default' setting each time would require another relay that monitors the state of the line and then we're getting into Plan 107 territory.

Given the OP is already using VoIP I think it's probably easier to keep the line/intercom switching in the VoIP arena.
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Old 18th Jun 2017, 1:17 am   #15
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Default Re: House intercom situation (again)

Quote:
Originally Posted by julie_m View Post
Without wanting to sound too much like a broken record, a scrap PC with the free Asterisk software and a hardware card providing FXS (phone) and FXO (exchange line) ports will let you do all manner of funky stuff.
I gave up running Asterisk on a PC back in the Trixbox days, due to intense lobbying by my electricity meter I now run Asterisk (RASPBX) on a Raspberry Pi and use ATAs to interface to POTS.

To the OP, I have programmed a Linksys PAP2 as a stand-alone mini PABX so that two flatmates can dial out on separate VoIP accounts and dial each other internally FXS>FXS
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