Up until the mid-1980s, connecting a computer to a phone line was tricky: many phone companies didn’t allow the connection of unlicensed equipment to their network, and even if they did, you might still find yourself blocked by a lack of standardized connectors. A simple workaround for all this was an acoustic coupler, a device that played your modem’s sounds directly into a phone’s receiver without any electrical connection. Modem speeds were slow anyway, so the limited bandwidth inherent in such a system was not much of a problem.
Nowadays it’s easier to find an internet connection than a phone line in many places, but if you’re stuck in an ancient hotel in the middle of nowhere you might just find [GusGorman]’s modern take on the acoustic coupler useful. The basic design is quite simple: it’s a 3D-printed box with two cups that fit a typical phone handset and a space to put a USB speaker and microphone. Thanks to minimodem it’s easy to set up a connection with any other computer equipped with a phone connection.
The maximum speed achievable with this setup is between 100 and 300 bits per second, so using it for anything more than text-based messaging is pretty much impossible. [Gus] therefore also designed a simple BBS-like system that can be used to acces things like weather reports and cryptocurrency wallet information. Thanks to VoIP, the server doesn’t need a physical phone line and could even be running on a cloud computing service.
The BBS system is quite limited as of now, but can easily be adapted to interface with any kind of online service. We’ve seen a similar setup in a teletype that queries Wolfram Alpha, for example. Although acoustic couplers have been obsolete for decades, they still sometimes come in handy for circumventing internet censorship.