modem

69 Articles

Tiny UPS Keeps WiFi Online

October 24, 2025 by 29 Comments

For any mission-critical computer system, it’s a good idea to think about how the system will handle power outages. At the very least it’s a good idea to give the computer enough time to gracefully shut down if the power outage will last for an indefinite time. But for extremely critical infrastructure, like our home Wi-Fi, we might consider a more long-term battery backup that can let us get through the longest of power outages.

Part of why this project from [Next Builder] works so well is that most off-the-shelf routers don’t actually use that much energy. Keeping that and a modem online when the power is out only requires a few lithium batteries. To that end, three lithium ion cells are arranged in series to provide the router with between 9 and 12 volts, complete with a battery management system (BMS) to ensure they aren’t over- or under-charged and that they are balanced. The router plugs directly into a barrel jack, eliminating any switching losses from having to use an inverter during battery operation.

While [Next Builder] is a student who lives in an area with frequent interruptions to the electricity supply, this does a good job of keeping him online. If you’re planning for worse or longer outages, a design like this is easily adapted for more batteries provided the correct BMS is used to keep the cells safely charged and regulated. You can also adapt much larger UPS systems to power more of your home’s electrical system, provided you can find enough batteries.

Making WiFi Sound Like Dial-Up Internet

October 24, 2025 by 24 Comments

Dial-up modems had a distinctive sound when connecting, with the glittering, screeching song becoming a familiar melody to those jumping online in the early days of the Internet. Modern digital connections don’t really have an analog to this, by virtue of being entirely digital. And yet, [Nick Bild] decided to make WiFi audible in a pleasing tribute to the modems of yore.

The reason you could hear your dial-up modem is because it was actually communicating in audio over old-fashioned telephone lines. The initialization process happened at a low enough speed that you could hear individual sections of the handshake that sounded quite unique. Ultimately, though, once a connection was established at higher speed, particularly 33.6 k or 56 k, the sound of transmission became hard to discern from static.

Modern communication methods like Ethernet, DSL, and WiFi all occur purely digitally — and in frequencies far above the audible range. Thus, you can’t really “listen” to a Wi-Fi signal any more than you can listen to the rays of light beaming out from the sun. However, [Nick] found an anachronistic way to make a sound out of WiFi signals that sounds vaguely reminiscent of old-school modems. He used a Raspberry Pi 3 equipped with a WiFi adapter, which sniffs network traffic, honing in on data going to one computer. The packet data is then sent to an Adafruit QT Py microcontroller, which uses the data to vary the amplitude of a sound wave that’s then fed to a speaker through a digital-to-analog converter. [Nick] notes this mostly just sounds like static, so he adds some adjustments to the amplitude and frequency to make it more reminiscent of old modem sounds, but it’s all still driven by the WiFi data itself.

It’s basically WiFi driven synthesis, rather than listening to WiFi itself, but it’s a fun reference to the past. We’ve talked a lot about dial-up of late; from the advanced technology that made 56 k possible, to the downfall of AOL’s long-lived service. Video after the break.

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YouTube… Over Dial Up

September 29, 2025 by 25 Comments

In the days of yore, computers would scream strange sounds as they spoke with each other over phone lines. Of course, this is dial up, the predecessor to modern internet technology, offering laughable speeds compared to modern connections. But what if dial up had more to offer? Perhaps it could even stream a YouTube video. That’s what the folks over at The Serial Port set out to find out.

The key to YouTube over dial up is a little known part of the protocol added right around the time broadband was taking off called multilink PPP. This protocol allows for multiple modems connected to a PC in parallel for faster connections. With no theoretical limit in sight, and YouTube’s lowest quality requiring a mere 175 Kbps, the goal was clear: find if there is a limit to multilink PPP and watch YouTube over dialup in the process.

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Acoustic Coupling Like It’s 1985

August 27, 2025 by 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 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 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 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!