Acoustic Coupler Pole-Vaults Over China’s Firewall


[agp.cooper]’s son recently went to China, and the biggest complaint was the Great Firewall of China. A VPN is a viable option to get around the Great Firewall of China, but [agp] had a better idea: an acoustic coupler for his son’s iPhone.

Hackaday readers of a recent vintage might remember an old US Robotics modem that plugged into your computer and phone line, allowing you to access MySpace or Geocities. Yes, if someone picked up the phone, your connection would drop. Those of us with just a little more experience under our belts will remember the acoustic coupler modem — a cradle that held a phone handset that connected your computer (indirectly) to the phone line.

With a little bit of CNC work, [agp] quickly routed out a block of plywood that cradled his son’s iPhone. Add in a speaker and a microphone, and that’s an acoustic coupler. There’s not much to it, really. The real challenge is building a modem.

In the late 90s, there were dedicated chipsets for modems, and before that, there was a 74xx-series chip that was a 300-baud modem. [agp] isn’t using anything like that. He’s building a modem with an Arduino. This is a Bell 103A-compatible modem, allowing an iPhone to talk to a remote computer at 300 bits per second. This is a difficult challenge; we’re not able to get 33kbps over a smartphone voice connection simply because of the codecs used. However, with a little bit of work, [agp] managed to build a real modem with an Arduino.



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