Hacking History: Old Crank Telephones Talk Again Thanks to Open Source Tools

Open Hardware
Location: Portland 251
Average rating: ****.
(4.00, 3 ratings)

The stock of original-condition antique magneto telephones has diminished through the years, in part because there has been no practical way to use them on the public switched telephone network (PSTN) without modifying the original hardware, which usually results in the original configuration of the sets to be permanently altered.

MAG-NET, a project undertaken by the Computer Science department at Saint Joseph’s College in Indiana, uses Open Source tools and a cheap home-made external hardware interface to allow old crank phones to be placed back into service without any modification to the sets. An additional feature is that the original use case is preserved, whereby the user (“subscriber” in telephone parlance) twists the crank and hears the classic operator’s prompt, “Number, please?” In our case, however, the operator is a voice recognition module running on an Asterisk server, which parses the subscriber’s voice commands and completes the call. The processor can even handle old-fashioned telephone numbers, which included a place name along with a (usually small) integer number, e.g. “Connect me to Medaryville, Indiana 1.”

MAG-NET was modeled after C-NET, an existing network of antique telephones which uses Asterisk as the glue to connect together antique telephones and telephone switching equipment located all over the world. A gateway allows MAG-NET members to interoperate with C*NET phones.

Several challenges were overcome, most notably the dangers A/C ring voltages, which can cause painful shocks, and which were not “designed out” of original telephone equipment, which often fail to provide proper grounding.

The hardware interface would make Rube Goldberg proud: we use X-10 powerline communications technology, driven by the Open Source heyu package under the control of Asterisk, to connect telephones to the network when an incoming call arrives. Outgoing calls drive an alternating relay to “bring up the line,” and a poor-man’s solution dispenses with both to allow a simple light switch to control network access for the set.

The antique telephone is connected through the interface circuit to an ATA, which in turn is connected to a dedicated Asterisk server, installed on a cheap commodity router running the openWRT distribution of Linux.

The next phase of the project will allow magneto switchboards to provide MAG-NET “trunks” to volleys of telephones connected to them, establish a global namespace of magneto sets and switches, and provide failover services to allow 24×7×365 operation along with actual live operator service.

We hope our project will provide collectors an incentive to keep their magneto phones in original condition. Our provision of historically correct use capability allows people who may have never seen one of these telephones to enjoy a piece of living history that provides both a window into the past, and a glimpse at the unbroken chain of technology that has led to the modern telephone network we enjoy today.

Photo of Brian Capouch

Brian Capouch

Saint Joseph's College

Brian Capouch is a longtime open source user, programmer, and hacker. In 2016, Brian retired from Saint Joseph’s, a small Indiana college, where he taught CS using 100% open source tools. He is heavily involved in a number of historical restoration projects. The modern web, full stack universal JavaScript, SPAs, and PWAs are his current passions.

Comments on this page are now closed.


Picture of Dan DeBrito
Dan DeBrito
07/28/2011 7:36am PDT

Photos could have been better quality.