Acoustic Coupling Like It’s 1985

August 27, 2025 by Bryan Cockfield 20 Comments

Before the days of mobile broadband, and before broadband itself even, there was a time where Internet access was provided by phone lines. To get onto a BBS or chat on ICQ required dialing a phone number and accoustically coupling a computer to the phone system. The digital data transmitted as audio didn’t have a lot of bandwidth by today’s standards but it was revolutionary for the time. [Nino] is taking us back to that era by using a serial modem at his house and a device that can communicate to it through any phone, including a public pay phone.

As someone in the present time can imagine, a huge challenge of this project wasn’t technical. Simply finding a working public phone in an era of smartphones was a major hurdle, and at one point involved accidentally upsetting local drug dealers. Eventually [Nino] finds a working pay phone that takes more than one type of coin and isn’t in a loud place where he can duct tape the receiver to his home brew modem and connect back to his computer in his house over the phone line like it’s 1994 again.

Of course with an analog connection like this on old, public hardware there were bound to be a few other issues as well. There were some quirks with the modems including them not hanging up properly and not processing commands quickly enough. [Nino] surmises that something like this hasn’t been done in 20 years, and while this might be true for pay phones we have seen other projects that use VoIP systems at desk phones to accomplish a similar task.

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Why 56k Modems Relied On Digital Phone Lines You Didn’t Know We Had

March 6, 2025 by Lewin Day 51 Comments

If you came of age in the 1990s, you’ll remember the unmistakable auditory handshake of an analog modem negotiating its connection via the plain old telephone system. That cacophony of screeches and hisses was the result of careful engineering. They allowed digital data to travel down phone lines that were only ever built to carry audio—and pretty crummy audio, at that.

Speeds crept up over the years, eventually reaching 33.6 kbps—thought to be the practical limit for audio modems running over the telephone network. Yet, hindsight tells us that 56k modems eventually became the norm! It was all thanks to some lateral thinking which made the most of the what the 1990s phone network had to offer.

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A Modem As A Cassette Interface

January 24, 2025 by Jenny List 20 Comments

At least some in the audience will at some time in the distant past have loaded or saved a program on cassette, with an 8-bit home computer. The machine would encode binary as a series of tones which could be recorded to the tape and then later retrieved. If you consider the last sentence you’ll quickly realize that it’s not too far away from what a modem does, so can a modem record to cassette and decode it back afterwards? [Jesse T] set out to give it a try, and as it turns out, yes you can.

The modem talks and listens to the cassette recorder via circuitry that provides some signal conditioning and amplification, as well as making a dial tone such that the modem thinks it’s talking to a real phone line. An Arduino steps in as dial tone creator.

Of course, this is hardly a viable solution to 21st century data storage need, but that’s hardly the point as it’s a cool hack. We like it, and oddly we’ve seen a similar technique used with a retrocomputer in the past.

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A Quarter And A Dime Will Get You A Commodore 64 Softmodem

January 20, 2025 by Lewin Day 43 Comments

Back in the 1980s, a viable modem cost hundreds of dollars. Even in the 1990s, you were looking at spending a a Benjamin or two to get computer squawking down the phone lines. According to [Cameron Kaiser], though, it’s possible to whip up a softmodem using a Commodore 64 for much cheaper than that. How much? Just 35 cents, we’re told!

The inspiration was simple—Rockwell apparently used to build modems using the 6502. The Commodore 64 has a 6502 inside, pretty much, so surely it could be a softmodem, right? Indeed, one [John Iannetta] had done this in a one-way form in the 1980s, using the Commodore 64’s SID audio chip to output data in sound form. In 1998, he espoused the 35-cent modem—basically, the price of buying an RCA jack to hook up a phone line to your Commodore 64.

As [Cameron] found out, the concept still works today, as does [John’s] code, but it’s more like 68 cents in 2025 dollars. With the right bits and pieces, and a little code, you can have your C64 modulating data into sound at rates of 300 baud.

It’s hacky, slow, and there’s no real way to receive—the C64 just doesn’t have the chops to demodulate these kinds of signals on its own. You also shouldn’t use it on a real phone line if you don’t want to damage your C64. Still, it’s a wonderful bit of hackery, and it’s fun to see how well it works. We’ve seen some other great Commodore 64 modem projects before, like the ever-useful RetroModem. Meanwhile, if you’ve got your own communication hacks for the computers of yesteryear, don’t hesitate to let us know!

Getting Dial-Up To Work Over VOIP Isn’t Always Easy

December 19, 2024 by Lewin Day 26 Comments

Dial-up modems used to be the default way of accessing the Internet, but times have moved on. They’re now largely esoteric relics from a time gone by. With regular old phone lines rather hard to come by these days, [Peter Mount] decided to try getting a pair of dial-up modems working over VoIP instead.

The build started with a pair of Linksys PAP2T VoIP phone adapters, which were originally designed for hooking regular phones up to VoIP systems. He paired each US Robotics modem with a PAP2T, and then hooked both into a VoIP Private Branch Exchange which he set up using 3cx on a Raspberry Pi 3B+. The Pi also acted as a server for the modems to connect to. It took a lot of fiddly configuration steps, but he found success in the end. On YouTube, he demonstrates the setup—with that glorious modem sound—communicating successfully at a rate of 9600 baud.

It’s nice to see this vintage hardware communicating in a what is effectively a simulated world created entirely within modern hardware. We’ve seen similar projects before, like this attempt to get dial-up going over Discord. If you’re doing your own odd-ball screechy communications experiments, don’t hesitate to drop us a line!

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The Tsushin Booster – A PC Engine Modem Add-on With A Twist

November 2, 2024 by Dave Rowntree 5 Comments

Sometimes, hardware projects get cancelled before they have a chance to make an impact, often due to politics or poor economic judgment. The Tsushin Booster for the PC Engine is one such project, possibly the victim of vicious commercial games between the leading Japanese console manufacturers at the tail end of the 1980s. It seems like a rather unlikely product: a modem attachment for a games console with an added 32 KB of battery-backed SRAM. In addition to the bolt-on unit, a dedicated software suite was provided on an EPROM-based removable cartridge, complete with a BASIC interpreter and a collection of graphical editor tools for game creation.

Internally, the Tsushin booster holds no surprises, with the expected POTS interfacing components tied to an OKI M6826L modem chip, the SRAM device, and what looks like a custom ASIC for the bus interfacing.

It was, however, very slow, topping out at only 1200 Baud, which, even for the period, coupled with pay-by-minute telephone charges, would be a hard sell. The provided software was clearly intended to inspire would-be games programmers, with a complete-looking BASIC dialect, a comms program, a basic sprite editor with support for animation and even a map editor. We think inputting BASIC code via a gamepad would get old fast, but it would work a little better for graphical editing.

PC Engine hacks are thin pickings around these parts, but to understand a little more about the ‘console wars’ of the early 1990s, look no further than this in-depth architectural study. If you’d like to get into the modem scene but lack original hardware, your needs could be satisfied with openmodem. Of course, once you’ve got the hardware sorted, you need some to connect to. How about creating your very own dial-up ISP?

A Brand New USB Modem In The 2020s

September 17, 2024 by Jenny List 11 Comments

The dulcet tones of a modem handshake may be a thing of the distant past for most of us, but that hasn’t stopped there being a lively hacking scene in the world of analogue telephones. Often that’s achieved using old devices resurrected from a parts bin, but sometimes, as with [Brian]’s USB modem, the devices are entirely new.

A surprise is that modem chips are still available, in this case the SkyWorks IsoModem chips. It uses an M.2 module format to allow the modem and support circuitry to be separated enough to place it in another project if necessary, along with a clear warning on the PCB not to put it in the identical-looking PC slot. It also comes with tips for experimenting if you don’t have access to a landline too, given that POTS is fast becoming a thing of the past itself in so many places.

If you’ve got nowhere to show off your modem, we’d like to suggest you try a hacker camp. There you’ll often find a copper network you’re positively expected to hack.