Old School Phone-Based Modem Uses Two Cans and a String to Send Data

Most of us take advantage of cable, DSL, FIOS, or wireless connections to gain access to the internet, which offers speeds capable of streaming 2K video, playing games, researching, and other activities easily and efficiently. It’s something a lot of us take for granted until the connection goes down. Kids today don’t know the excitement (and frustrations) of having a dialup connection that produced the intricate screeching/beeping/static sounds while connecting to the early internet to hit-up the latest information on BBS sites.

Those same kids might not know the joys of talking to friends or family members using a pair of tin cans and a length of string either, but one software engineer with time to spare has merged both technologies to create a tin can phone modem capable of transmitting data. As easy as that might sound, Michael Kohn had a difficult time getting his project to work, certainly so when it came to the tin can part, trying conical tin cans and empty Starbucks latte cups, before settling for cardboard/tin cans.

Kohn also went through the same trial and error process for choosing the necessary cordage to link the cans. He tested using dental floss and fishing line, before selecting plain kite string, as transmitting and receiving data works more efficiently using non-stretchable material. At either end of the string is a transmitter and receiver, both of which feature a similar circuit design with the transmitter using an ATtiny2313 and an LM386 audio amplifier, and an MSP4340 microcontroller and LM566 tone decoder for the receiver.

The modulation is kept simple as well and uses a 400MHz tone (with varying length depending on ones and zeros) to transmit data, which Kohn demonstrated by sending his name over a pair of terminal programs, and a kite string held taught by two kitchen chairs. A complete walkthrough of his build can be found on his blog for those interested in recreating his project.