Field Phone Concept

The Field Phone project is your own personal telephone company! This project allows you to use normal wired telephones for communication within and between buildings and shelters, either for everyday convenience or for security in a crisis when the normal telephone system might not be available.
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Field Phone Concept

Postby softbaugh » Wed Apr 13, 2016 3:15 am

At an event in North Carolina back in October, 2015, Shane Bean approached our product manager about a concept he had for communication in a crisis, such as neighborhood defense against rampaging zombie hordes. Shane's idea was to re-use old telephone handsets to communicate between buildings or defensive positions if the phone company (cellular or landline) wasn't able to provide service. Another attendee at that event suggested supporting amateur radio headsets in such a system. This was the birth of the field phone concept, incorporating the following features:

- Use of existing telephone equipment. While the original concept was to use the RJ12 handsets featured on many phones, the wide variety of features and electrical interfaces on these handsets made the original goal impractical. As a result, we decided to interface the phones directly at the telco RJ11 interface instead.
- Use of improvised field wiring, including such ad-hoc wiring as barbed-wire fencing, in addition to normal telco wiring or military-style "slash" wire.
- Discreet ring or call indication to replace the normally noisy and disruptive telco ring and ring voltages.
- Rechargeable battery backup power, but otherwise operable from a wide range of input power sources. 12v car batteries and typical mid-voltage solar panels were to be specifically supported.
- Optional support for amateur radio headsets, or various PC headsets.
- Open-source so that others could improve the design or build their own components.
- Because it supports off-the-shelf wired phones, this system is not designed to replace robust weather-proof field phones such as the military TA-312 or similar ruggedized phone sets. However, this system can fill the role of such ruggedized units in limited, protected ways, saving those units for where they are really needed. A suitable application for the field phone system would be between homes, barns or other shelters.

The resulting design is the Field Phone, which emulates a landline telco interface. The core module supports charging and operating from a rechargeable lithium iron phosphate battery in the popular 18650 format. It can charge from a wide range of input voltage sources, from 6v all the way up to 30v, which handles most popular lead acid battery topologies, as well as all but the very largest solar modules. This module, with intermittent call usage, can operate for days on a single charge, and supports several phones (the exact number varies depending on the specifics of each phone model). It also provides two independent phone circuits, which can be bridged either with a hardware jumper, or with the conference feature of a two-line phone sitting astride the master connection.

The center pair of a typical 4-wire telco wire supports the phone interface itself. Optional ring functionality is supported on the outer wire pair by inserting a Ring Interface Module. The default ring interface module provides a LED indicator in silent mode, or a small, quiet piezo buzzer which can be disabled by a jumper. Future Ring Interface Modules will support a variety of headsets, allowing the superior magnetics of those devices to increase battery life, increase the available number of stations on a circuit, or both.

This portion of the SoftBaugh forum is designed to increase the state of the field phone art, as well as make the open source portions of this project available. Browse through the forum, and share your experience and thoughts about this community project!
Last edited by softbaugh on Wed Apr 13, 2016 5:14 am, edited 1 time in total.

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Re: Field Phone Concept

Postby sauced07 » Thu Apr 21, 2016 5:17 pm

This is Shane, I would like to give some more thoughts to the project. My whole goal was dependable, rechargeable secure communications. This project fits the bill. I am clueless as to electronics and these guys did a remarkable job of creating a plug n play system. I received a prototype and literally had it up and running in minutes( once I realized it took the whole phone. Standing in front of the wife with a handset to both ears saying " hello" is not something I will live down for a while). For each phone I used a simple trimline phone from Walmart that cost around $10 each. I also purchased a small Plano ammo box to store the phone in for $5. That box also stores a compass, maps, waterproof pads and writing utencils.That box fits in a sustainment pouch on a molle ruck so it is very portable. Essentially once the wire is ran where you want it, you open the box, plug in your wires and your up and running.
I'm sure many people will think of there own setups for this system. I currently live in an old farmhouse surrounded with fields and woods. My original plan for this system was to setup the main unit at the house and run wire out to overwatch positions on my perimeter giving constant communications in the event such actions would be warranted. My situation will be changing as I am moving to a more urban setting. I have already come up with a new plan for this system, I love the versatility of it.
I am interested in hearing other ideas for this system from people. I'm sure some will come up with ideas that I hadn't thought of.

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Re: Field Phone Concept

Postby mobius » Tue Oct 25, 2016 2:58 pm

Could you run alarm signaling through this system?

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Re: Field Phone Concept

Postby softbaugh » Wed Oct 26, 2016 1:35 am

Hi mobius,

Good question, and maybe. What kind of alarm signals are you interested in using?

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