Dispatcher phone system for a large layout

[bdennis]

Gent,
Just looking for some assistance with finding a circuit that will work as a dispatcher phone system.
Here is the idea.
I am building a large layout in a 7.5meter x 6meter room.
The layout will have 6 or 7 towns plus a dispatcher that will operatate the CTC panel via JMRI.
I have found (and bought) a number of these hand sets and plan to use them for each town and the dispatcher.
http://www.ebay.com.au/itm/Coco-Phone-Retro-Cell-Phone-Handset-3-5mm-for-Iphone-OZ-seller-/221250125290?pt=AU_MobilePhoneAccessories&hash=item338388fdea

The hand set is basically a 4 pin plug (RJ11 on the hand set end) and a 3.5mm 4 connection plug on the other end of the cable.
So the Mic and the speaker are separate and the speaker has a volume control on the side.

In terms of communicating with the dispatcher to get his attention, I can have a separate circuit with a button at the town and a bell at the dispatchers desk. So the phone circiut does not need a on / off hook function.

I imagine the circuit to be effectively a party line, where if 1 person is on the line to the dispatcher and another one picks up the hand set, then he will also hear the conversation and just wait for it to finish before talking to the dispatcher.
If it is easier to have a rotary switch to enable each hand set to talk then so be it.

So thats the idea, and the hand sets that I have.

Does anyone have a circuit or any ideas as to how I can achieve what I need.?

I am very comfortable with using a soldering iron and electronic components, IC's etc etc.. So if the circuit has a number of parts then thats perfectly ok.

So any ideas would be greatly appreciated.

Regards
Brendan.

[mrp]

There was a series in the OP SIG magazine (The dispatcher's office) that covered telephones. It was written by Seth Neumann.
It covers just about everything you need to know for telphones on a model railroad

[C855B]

I have one of these iPhone handsets, and you know what? You make me wonder if it will work with a so-called "family radio". I'll have to go find my radios and try it out. If this works, your solution might be off-the-shelf plug-in, with no wires to run.

No, this doesn't violate your concept - "party line" style dispatcher phones were push-to-talk. The old-fashioned station operator console, with the phone suspended on a scissor mount, actually had a push-to-talk treadle below the desk. There wasn't a call button, the dispatcher was always on, it was the station operator who had the bell or buzzer to interrupt his nap.

[conrail98]

I have one of these iPhone handsets, and you know what? You make me wonder if it will work with a so-called "family radio". I'll have to go find my radios and try it out. If this works, your solution might be off-the-shelf plug-in, with no wires to run.

Another solution I've seen with little to no wiring is the use of the cordless phones that have the ability to be expanded with additional phones. Here are two links from one layout that uses them:

http://shendiv.wordpress.com/2010/09/26/using-wireless-phones/
http://shendiv.wordpress.com/2011/03/21/update-on-using-wireless-phones/

Another layout I operate on is going to test using them for direct communication between the dispatcher and yard operators since the yard operators generally don't operate with headsets,

Phil

[John]

buy some cheap old style phones .. princess style is good .. run telephone cord to each station, plug the phones in  .. add a 6 volt battery to the red/green wire IIRC, and you have a neat phone system .. add another couple of wires for a buzzer to each station  from teh DS desk .. those phones are 5-6 bucks at RESTORE

[bdennis]

Gents,
Thanks for the tips.

As mentioned, I am committed to the hand sets I have. So easgerly waitig for Mike's update re the "family radio" idea.

Thanks.

Brendan

[C855B]

Welllllll... the family radio experiment was a qualified success. At minimum, it certainly is the seed of an idea. I plugged the iPhone-compatible 3.5mm into the handset jack on the radio - it started transmitting, and I could speak into the handset mic and hear it from the speaker on the other radio. However, it was transmitting full-time, no control from the "PTT" (iPhone "answer") button.

The Yaesu family radios I have are fairly old, designed like small ham radio HTs (handi-talkies), with three-circuit 3.5mm plugs in the handset connection rather than four because it doesn't have stereo audio output. That means two things:

1) The PTT function on the radio works by switching the mic in and out of the circuit, and when the radio "sees" the mic connected, it transmits. In other words, if I rewired the handset to have the PTT button control the mic wire, it should work.

2) I truly have to wonder if more current family radio designs support the de-facto standard iPhone scheme, and the PTT logic and possibly even volume control is from the button wire logic. It would be worth borrowing one to try.

I didn't, or rather, couldn't test to see if the handset speaker worked as it should, since the radio was in transmit mode. I would expect it to be OK.

[railnerd]

Seth's clinic about phone systems he gave at X2011West can be found here:

http://www.x2011west.org/handouts/Communications-for-Model-Railroads.pdf

-Dave

[bdennis]

Gents,
I think I have found the solution I was looking for

http://www.cameratim.com/electronics/intercom/intercom-design-june-2010.pdf

Regards
Brendan