We’re suckers for alternative data transmission methods, and [Georgi Gerganov]’s ggwave made us smile. At its core, it’s doing what the phone modems of old used to do – sending data encoded as different audio tones. But GGwave does this with sophistication!

It splits the data into four-bit chunks, and uses 16 different frequency offsets to represent each possible value. But for each chunk, these offsets are added to one of six different base frequencies, which allows the receiving computer to tell which chunk it’s in. It’s like a simple framing concept, and it makes the resulting data sound charmingly like R2-D2. (It also uses begin and end markers to be double-sure of the framing.) The data is also sent with error correction, so small hiccups can get repaired automatically.

What really makes ggwave shine is that it’s ported to every platform you care about: ESP32, Arduino, Linux, Mac, Windows, Android, iOS, and anything that’ll run Python or JavaScript. So it’ll run in a browser. There’s even a GUI for playing around with alternative modulation schemes. Pshwew! This makes it easy for a minimalist microcontroller-based beeper button to control your desktop, or vice-versa. An ESP32 makes for an IoT-style WiFi-to-audio bridge. Write code on your cell phone, and you can broadcast it to any listening microcontroller. Whatever your use case, it’s probably covered.

Now the downside. The data rate is slow, around 64-160 bits per second, and the transmission is necessarily beepy-booopy, unless you pitch it up in to the ultrasound or use the radio-frequency HackRF demo. But maybe you want to hear when your devices are talking to each other? Or maybe you just think it’s cute? We do, but we wouldn’t want to have to transmit megabytes this way. But for a simple notification, a few bytes of data, a URL, or some configuration parameters, we can see this being a great software addition to any device that has a speaker and/or microphone.

Oh my god, check out this link from pre-history: a bootloader for the Arduino that runs on the line-in.

Retrocomputers are fun, but ultimately limited in capability compared to modern hardware. One popular pursuit to rectify this is the connection of early home computers to the Internet. To that end, [que] built the Retromodem for the Commodore 64.

The build starts with a case from an Intel 14.4 modem. A little fast for the Commodore 64 era, but anachronism is charming when done tastefully. Inside is an Arduino with an ethernet module to handle the heavy lifting of carrying packets to the outside world.  [que] took the time to wire up status LEDs for the proper vintage look, which really adds something to the project. They switch on and off to indicate the various settings on the modem – it’s great to see in the video below the break the “HS” LED light up when the baud rate is changed to a higher speed.

The project implements most of the Hayes command set, so you can interface with it over a serial terminal just like it’s 1983. [que] doesn’t go into too many details of how it’s all put together, but for the experienced code warrior it’s a project that could be whipped up in a weekend or two. For a more modern take, perhaps you’d like to hook your C64 up over Wifi instead?

[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.

Where you might see a can, [Adam Kumpf] sees a robot. [Adam’s] robot (named [Canny]) doesn’t move around, but it does have expressive eyebrows, multicolored eyes, and a speaker for a mouth. What makes it interesting, though, is the fact that it receives audio commands via the headphones it wears. You can see [Canny] in action in the video below.

The headphones couple audio tones to [Canny’s] microphone using AFSK (audio frequency shift keying). [Canny] uses an opamp to bring the microphone level up and then uses a 567 PLL IC to decode the audio tones. [Adam] selected two clever frequencies for the mark and space (12345 Hz and 9876 Hz). In addition to being numerically entertaining, the frequencies are far enough apart to be easy to detect, pass through the headphones with no problem, and are not harmonically related.

The 567 IC detects only one of the tones. Ignoring one tone is not always great for noise rejection, but for this use should be more than adequate and cuts the parts count down. To avoid false commands, the data contains markers, lengths, and checksums. The 567 feeds the Arduino, which handles all the robot control.

How do you create the sounds that go to the headphones? You use a Web page. Of course, you could generate the low baud rate tones in other ways, too. AFSK modems are common in Ham radio circles, and there are certainly plenty of modem designs. Then again, there is something pleasing about the simplicity of this circuit. The appeal of [Canny] doesn’t hurt any, either.

In the old days, a serial port often connected to an acoustic coupler that gripped a phone handset and allowed a remote connection to a far away serial port (via another phone and acoustic coupler) at a blistering 300 baud or less. The acoustic coupler would do the job of converting serial data to audio and reconstituting it after its trip through the phone lines. Modems advanced, but have mostly given way to DSL, Cable, Fiber, and other high speed networking options.

In a decidedly retro move, [James Halliday] and [jerky] put a modern spin on that old idea. They used the webaudio API to send serial data to a remote Arduino. The hack uses a FET, a capacitor, and a few resistors. They didn’t quite build a real modem with the audio. Instead, they basically spoof the audio port into sending serial data and recover it with the external circuitry. They also only implement serial sending (so the Arduino receives) so far, although they mention the next step would be to build the other side of the connection.

They say the data transmission is finicky, but it works (see the video below). We imagine using proper modem tones and decoders might work better, but would be a lot more effort. We’ve covered a 1200 baud modem before. We’ve also covered a bit of the theory behind them.