Closed system intercom between 2 746's ??

[russell_w_b]

Originally Posted by DAVEHALL

'with a transmission bridge in the house ,supplying transmission current to both phones, and on lift off of the distant one , giving an alarm to the house'

...Being just the type of thing I described and illustrated in posts 4, 9 and 15!

[AlanBeckett]

Possibly I'm missing the point here - bear with me.
A friend of mine has a fairly large house over three floors, and he got fed up of trying to contact the children on the third floor. The solution was to buy and install a PABX, and wire up extensions in all the rooms. Of course you have to dial 9 to get out, but the good side is that the person who answers can divert the call to whoever wants it. Also, they can talk among themselves.
Thse 'little' exchanges are readily available.
Alan

[russell_w_b]

Far too sensible, Alan! But certainly a good excuse to connect, use, and put on show all one's telephone collection in a working capacity.

Wonder what Mrs Barnes would say to a Krone cabinet on the wall?

[Tractorfan]

Hi,
Years ago I remember connecting two 'phones together in parallel and I put a choke in series with the 30-ish volt DC supply. When the dial was pulled round it rang the bell at the other end the corresponding number of times. I think the choke helped produce the pulses.
My young (then) nieces had great fun talking to each other from the house to the end of the garden. Alas I can't remember exactly how I connected the individual wires.
Cheers de Pete

[DAVEHALL]

On the topic of small systems -both BT and Panasonic brought out small two line /6 or 8 extension systems .Of the two ,the BT one did not require an expensive system phone to program, and the instructions were fairly simple .But that was approx six or more years ago . Seem to remember places like Comet sold them.Price did surprise me as being quite low .

Of course ,you could get hold of an old type ( minimaster /2+8 etc) and keep the theme olde worlde .

[DAVEHALL]

Originally Posted by russell_w_b

...Being just the type of thing I described and illustrated in posts 4, 9 and 15!

Whoops ,sorry russell -missed that .Possibly the idea of how to get a 746 working on LB mode diverted my gaze .

[Phil G4SPZ]

A pair of cheap 446MHz walkie-talkies are perfect for the required duty.

[russell_w_b]

Originally Posted by DAVEHALL

On the topic of small systems -both BT and Panasonic brought out small two line /6 or 8 extension systems .

One thing to look out for is whether the exchange will accept LD (pulse-dialling) telephones. Our 12 yr. old 'INDeX' system at work accepts analogue extensions on some ports, but DTMF (tone-dialling) instruments only.

[russell_w_b]

Originally Posted by Tractorfan

My young (then) nieces had great fun talking to each other from the house to the end of the garden. Alas I can't remember exactly how I connected the individual wires.

I'd forgotten about doing that! I did similar as a youth with two 332 instruments, but connected them both in series with the battery. The telephones would have been configured as 'pre-modification' with bell and internal capacitor in series across the incoming line.

They 'tinged' without a choke, so I must've disconnected the dial-off normal contacts so the bell wouldn't have been shunted.

[DAVEHALL]

Originally Posted by russell_w_b

One thing to look out for is whether the exchange will accept LD (pulse-dialling) telephones. Our 12 yr. old 'INDeX' system at work accepts analogue extensions on some ports, but DTMF (tone-dialling) instruments only.

Russell - the panasonic one definitely caters for both - and from memory .the BT one does as well . Even the old BT 2+8 caters for both LD & mf , the minimaster ,LD only. But I seem to remember that INDEX was a funny system ,in it's requirements .

[dagskarlsen]

Originally Posted by dagskarlsen

I have used this simple intercom design, it may be you need mecanical tuning of the clapper and bells to get it ringing on 50Hz, but i works for mee with Norwegian phones. http://img.photobucket.com/albums/v4...com_simple.jpg

It works this way, when you lit off the handset, and replace it all (2) telephones rings once. When the canversation is ended and both has putted the handset back, you get one more ring. Allmoast as on the old manual exanges.

dsk

I believe the most of us tried to answer on the orginal question.
The diagram over is the simplest I have managed to come over, and tested. you may use only 2 wires, and you may hook up more than 2 phones.

Rick you have herd a lot of other ideas too, and if you go for the internet way telephone adapter may get their own C*NET number too, and you will be able to connect directly to a lot of other telephone collectors too.

The PBX solution is what I have chosen at home (still connected to C*NET) but it is some more wiring, and fetling.

It would be interesting to know how you solve it.

Good luck.

dsk

[neon indicator]

Originally Posted by russell_w_b

I'd forgotten about doing that! I did similar as a youth with two 332 instruments, but connected them both in series with the battery. The telephones would have been configured as 'pre-modification' with bell and internal capacitor in series across the incoming line.

They 'tinged' without a choke, so I must've disconnected the dial-off normal contacts so the bell wouldn't have been shunted.

We did that as kids. Used the top and bottom fence wire and speaker wire to house and at tent at bttom of field/garden.
We used a 6V springy top battery, everything in series. No chokes needed.

The bells faintly dinged on dialling. Real field telephones work similar but have winder to generate 25V to 70V AC for bells.

[Waveguide]

Hello,

There is a ready-made circuit for this sort of application in ETI circuits nr 2 book. Page 68. If you can't get hold of it, let me know and I'll scan in it for you next week (scanner at work) and post it here. Phone A will ring when phone B's handset is removed from the cradle. Requires a 30V battery.
73, Alex.

[richwk1]

Originally Posted by dagskarlsen

I believe the most of us tried to answer on the orginal question.
The diagram over is the simplest I have managed to come over, and tested. you may use only 2 wires, and you may hook up more than 2 phones.

Rick you have herd a lot of other ideas too, and if you go for the internet way telephone adapter may get their own C*NET number too, and you will be able to connect directly to a lot of other telephone collectors too.

The PBX solution is what I have chosen at home (still connected to C*NET) but it is some more wiring, and fetling.

It would be interesting to know how you solve it.

Good luck.

dsk

Hi dsk
Thanks to everyone for all there reply's i have many options now and am not really sure which one to do. My main criteria i suppose is two fold, ease of installation or application and secondly cost. I have a basic knowledge of wiring phone but even simply diagrams are a bit out of my comfort zone ( I assemble and repair computers for a living ) where wiring diagrams are not used. So i think i may got the computer route as my workshop has an internet connection and this is a little more my area.

[G0MEM Michael]

Originally Posted by russell_w_b

I'd forgotten about doing that! I did similar as a youth with two 332 instruments, but connected them both in series with the battery. The telephones would have been configured as 'pre-modification' with bell and internal capacitor in series across the incoming line.

I seem to remember doing something similar myself, two old bakelite GPO phones, a long length of cable, and an old car battery. It worked surprisingly well.

[richwk1]

Just a quick update, i went the wiring and battery option just to see if i could get it to work. Wired a couple of 746's as per diagrams with a bit of spare 4 core exterior phone extension ( only two wires used ) and a 9v pp3 ( er sorry showing my age ) whatever the modern equivalent number is !!
It worked pretty well my only problem is that i don't have anything to use as a proper shunt so just shoved on a 3.3k resistor ( only thing i had and probably will be of no use !!) but even with my ham fisted attempt it worked pretty well.
I havn't tried any options to get them to ring each other yet ( that seams a little more difficult) and i now have to run about 30m of cable up the garden. Will a 9v battery be strong enough to run over that amount of cable run ??.
Anyway thanks to all who put forth their opinions they are very much appreciated and if anyone has any more useful comments regarding my setup
( or regarding my innovative shunt !!!) feel free.

Regards Rich

[AndiiT]

Hi,
9 Volts should be OK on a 30 Metre cable run, in reality you only require around 1.5 Volts for actual speech, the higher voltage on the PSTN being used to allow for longer cable runs.
If the voltage drop is does become a problem you could always wire two 9 Volt batteries in series or try a higher capacity one such as a PP9 (I think that they are still available), which should give a little more current.

For a more permanent power solution a 10 Volt "Wall wart" power supply, such as are used on some broadband modems and routers should do the trick.

Signalling wise the circuit using buzzers and relays shown in either post #4 or
post #9 should keep things simple and permit you to use a low voltage supply.

Regards
Andrew

[dagskarlsen]

Another simple diagram http://tinyurl.com/zwgex just popped up in my mind. Yes it works, using only 9V (smoke detector) batteries the resistor may be skipped, and the voltage may be only 9 or 18 volts depending on the line. (these lasts remarkably long)
The drawback is to the need of other ringers (buzzers).

Since you have 4 wires yo may use some 50 hz and a button for ringing. Supplied from a transformer with 40-80V out, and a cap of e.g.1 microfarad as overcurrent protection.

Or even the rough and dangerous way; from the mains, live thru a 0.22 microfarad capacitor end return to ground or neutral. you may use a ringer push-button, or the dial contacts orginally used to short out the receiver when dialling. And: do not touch any live parts!!!

dsk