Field Phone Open Source Production
Field Phone Open Source Production
The field phone module allows normal telephones to work as a privately wired communications network. Great for emergencies or just fun!
The field phone module allows normal telephones to work as a privately wired communications network. Great for emergencies or just fun! Read more
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 host board, 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 prototype already exists, and works. We are currently redesigning the host module board to reduce costs, and are asking for your help to offset production costs to make this system as affordable as possible.
Risks and challenges
Very few risks exist with this project. Our prototype works as desired, and we are simply redesigning to reduce production costs. Our company is experienced in product designs and bringing designs to market. This is the first open source project that we have sponsored and we are asking for help to make it a success. If this funding project is a success we will be considering many open source projects in the future!Learn about accountability on Kickstarter
- (30 days)