Try A PWMPot

[Stephen Woodward] is familiar with digital potentiometers but is also familiar with their limitations. That spurred him to create the PWMPot which performs a similar function, but with better features than a traditional digital pot. Of course, he admits that this design has some limitations of its own, so — as usual — you have to make your design choices according to what’s important to you.

Perhaps the biggest limitation is that the PWMPot isn’t useful at even moderately high frequencies. The circuit works by driving two CMOS switches into an RC circuit. The switches’ inverted phase tends to cancel out any ripple in the signal.

Continue reading “Try A PWMPot”

38C3: It’s TOSLINK, Over Long Distance Fibre

If you’ve owned a CD player or other piece of consumer digital audio gear manufactured since the 1980s, the chances are it has a TOSLINK port on the back. This is a fairly simple interface that sends I2S S/PDIF digital audio data down a short length of optical fibre, and it’s designed to run between something like a CD player and an external DAC. It’s ancient technology in optical fibre terms, with a lowish data rate and plastic fibre, but consider for a minute whether it could be adapted for modern ultra-high-speed conenctions. It’s what [Ben Cartwright-Cox] has done, and he delivered a talk about it at the recent 38C3 event in Germany.

if you’ve cast you eye over any fibre networking equipment recently, you’ll be familiar with SFP ports. These are a standard for plug-in fibre terminators, and they can be had in a wide variety of configurations for different speeds, topographies, and wavelengths. They’re often surprisingly simple inside, so he wondered if he could use them to carry TOSLINK instead of a more conventional network. And it worked, with the simple expedient of driving an SFP module with an LVDS driver to make a differential signal. There follows a series of experiments calling in favours from friends with data centre space in various locations around London, finally ending up with a 140 km round trip for CD-quality audio.

It’s an interesting experiment, but perhaps the most value here is in what it reveals to us about the way optical networking systems work. Most of us don’t spend our days in data centres, so that’s an interesting technology to learn about. The video of the talk itself is below the break.

Continue reading “38C3: It’s TOSLINK, Over Long Distance Fibre”

FLOSS Weekly Episode 815: You Win Some, You Lose Some

This week, Jonathan Bennett and Randal chat with Matija Å uklje about Open Source and the Law! How do Open Source projects handle liability, what should a Contributor License Agreement (CLA) look like, and where can an individual or project turn for legal help?

Continue reading “FLOSS Weekly Episode 815: You Win Some, You Lose Some”

Running AI Locally Without Spending All Day On Setup

There are many AI models out there that you can play with from companies like OpenAI, Google, and a host of others. But when you use them, you get the experience they want, and you run it on their computer. There are a variety of reasons you might not like this. You may not want your data or ideas sent through someone else’s computer. Maybe you want to tune and tweak in ways they aren’t going to let you.

There are many more or less open models, but setting up to run them can be quite a chore and — unless you are very patient — require a substantial-sized video card to use as a vector processor. There’s very little help for the last problem. You can farm out processing, but then you might as well use a hosted chatbot. But there are some very easy ways to load and run many AI models on Windows, Linux, or a Mac. One of the easiest we’ve found is Msty. The program is free for personal use and claims to be private, although if you are really paranoid, you’ll want to verify that yourself.

What is Msty?

Talkin’ about Hackaday!

Msty is a desktop application that lets you do several things. First, it can let you chat with an AI engine either locally or remotely. It knows about many popular options and can take your keys for paid services. For local options, it can download, install, and run the engines of your choice.

For services or engines that it doesn’t know about, you can do your own setup, which ranges from easy to moderately difficult, depending on what you are trying to do.

Of course, if you have a local model or even most remote ones, you can use Python or some basic interface (e.g., with ollama; there are plenty of examples). However, Msty lets you have a much richer experience. You can attach files, for example. You can export the results and look back at previous chats. If you don’t want them remembered, you can chat in “vapor” mode or delete them later.

Each chat lives in a folder, which can have helpful prompts to kick off the chat. So, a folder might say, “You are an 8th grade math teacher…” or whatever other instructions you want to load before engaging in chat.

Continue reading “Running AI Locally Without Spending All Day On Setup”

Tech In Plain Sight: Security Envelopes

You probably get a few of these things each week in the mail. And some of them actually do a good job of obscuring the contents inside, even if you hold the envelope up to the light. But have you ever taken the time to appreciate the beauty of security envelope patterns? Yeah, I didn’t think so.

The really interesting thing is just how many different patterns are out there when a dozen or so would probably cover it. But there are so, so many patterns in the world. In my experience, many utilities and higher-end companies create their own security patterns for mailing out statements and the like, so that right there adds up to some unknown abundance.

So, what did people do before security envelopes? When exactly did they come along? And how many patterns are out there? Let’s take a look beneath the flap.

Continue reading “Tech In Plain Sight: Security Envelopes”

Remotely Controlled Vehicles Over Starlink

Modern remote control (RC) radios are capable of incredible range, but they’re still only made for line-of-sight use. What if you want to control a vehicle that’s 100s of kilometers away, or even on the other side of the planet? Cellular is an option, but is obviously limited by available infrastructure — good luck getting a cell signal in the middle of the ocean.

But what if you could beam your commands down from space? That’s what [Thingify] was looking to test when they put together an experimental RC boat using a Starlink Mini for communications. Physically, there was no question it would work on the boat. After all, it was small, light, and power-efficient enough. But would the network connection be up to the task of controlling the vehicle in real-time?

Continue reading “Remotely Controlled Vehicles Over Starlink”

Making Sure Your Patch Cables Are Ready For RF Work

How do you know that your patch cables are good? For simple jumper wires, a multimeter is about all you need to know for sure. But things can get weird in the RF world, in which case you might want to keep these coaxial patch cable testing tips in mind.

Of course, no matter how high the frequency, the basics still apply, and [FesZ] points out in the video below that you can still get a lot of mileage out of the Mark 1 eyeball and a simple DMM. Visual inspection of the cable and terminations can reveal a lot, as can continuity measurements on both the inner and outer conductors. Checking for shorts between conductors is important, too. But just because the cable reads good at DC doesn’t mean that problems aren’t still lurking. That’s when [FesZ] recommends breaking out a vector network analyzer like the NanoVNA. This tool will allow you to measure the cable’s attenuation and return loss parameters across the frequency range over which the cable will be used.

For stubborn problems, or just for funsies, there’s also time-domain reflectometry, which can be done with a pulse generator and an oscilloscope to characterize impedance discontinuities in the cable. We’ve covered simple TDR measurement techniques before, but [FesZ] showed a neat trick called time-domain transformation, which uses VNA data to visualize the impedance profile of the whole cable assembly, including its terminations.

Continue reading “Making Sure Your Patch Cables Are Ready For RF Work”