Gus Gorman's 3D-Printed Acoustic Coupler Is a Low-Cost Homage to Classic Roadwarrior Communication
Housing a USB microphone and speaker, this throwback to classic computing connects to a custom BBS.
Tinkerer and vintage computing enthusiast Gus Gorman has brought back a classic of the roadwarrior's on-the-move arsenal: an acoustic coupler, designed to pair a computing system with a landline telephone handset.
"One of those pieces of tech that I've always really wanted is an acoustic coupler," Gorman explains, referring to a vintage piece of hardware that connected a computer to a telephone line by literally cradling a landline handset with a microphone to its speaker and a speaker to its microphone — meaning no wires were required, and it could even be used with payphones. "Unfortunately, they don't make them any more."
The solution, other than scouring the auction sites and hoping for a compatible and still-functional listing to appear: building a new one, using a 3D-printed housing and a USB microphone and speaker set. "The realistic goal I was shooting for was about 300bps [bits per second]," Gorman explains, "with minimal typos." The bill of materials, too, was designed to be minimal: a $6 miniature USB microphone in one end and a $12.50 USB speaker in the other, designed for connection to an external system.
"At my house I have my own PBX [Private Branch Exchange] set up," Gorman explains of where the acoustic coupler will find its use. Testing, however, revealed that acoustic coupler design is trickier than it may seem: while original hardware might reach 300bps without difficulty, Gorman's recreation hits about 100bps before errors creep into the transmitted text.
The hardware's of little use without software, of course, and for this Gorman put together a bulletin board system (BBS) based on Kamal Mostafa's minimodem, a software-based frequency-shift keying (FSK) modulator/demodulator (modem) compatible with USB audio devices.
"Another cool thing that I'd like to see," Gorman suggests of where the project could go in the future," is a Raspberry Pi cyberdeck version of [this] with an acoustic coupler. Something else I want to try doing is instead of using the phone lines to transmit this information is to do a radio version with walkie-talkies or something."
More information is available on Gorman's YouTube channel, while the STL file for the acoustic coupler housing and the source code for the BBS are available on GitHub under an unspecified open source license.