A Wheatstone Bridge Matches Your Pots

Sometimes the simplest hacks can be the most useful or ingenious, and such is the case with [Keri Szafir]’s method of ensuring that potentiometers used in audio devices are matched. If you consider a typical stereo amplifier for a moment, you’ll see two amplifiers in one box with a single volume control. Two channels, one knob? Volume knobs are ganged stereo potentiometers.

All potentiometers are not created equal, and particularly in the cheaper devices they may not have a consistently matched resistance across both pots and across their travel. This messes up the stereo balance, so naturally it’s worth selecting a part with good matching. [Keri] selects them not with his golden ears, but by wiring both pots together as a Wheatstone bridge. A meter between the two wipers would detect any current due to a mismatch.

A Wheatstone bridge is one of those handy circuits that has plenty of uses in both AC and DC measurements. We probably see them most often in a strain gauge.

A EuroRack synthesizer module with an oscilloscope in the background showing a waveform

Recreating The Sounds Of The ’90s With A YM3812 Synthesizer

One reason the x86 PC became the dominant game platform in the early 1990s was the availability of affordable sound cards like the AdLib and Sound Blaster. These provided a quantum leap in sound quality compared to the PC speaker’s tinny beeps, thanks to Yamaha’s YM3812 chip, also known as OPL2. [Tyler] has made a detailed study of the various OPL series chips and wrote a comprehensive guide describing their operation.

[Tyler] begins by explaining the theory of FM synthesis. The basic idea is that you generate sine waves of different frequencies, combine them through mixing and modulation, and then adjust their strength over time. This way, a few simple operations on the chip’s nine sound channels can generate an astonishing variety of sounds from clear notes to chaotic noise. He then delves into the details of the YM3812 chip, including its 279 different register settings that enable all these operations.

The final goal of [Tyler]’s research is the design of a YM3812 EuroRack module that fits inside standard modular synthesizers. He’ll go into detail on the board’s design and construction in future blog posts, but he already shows the finished product and demonstrates its features in the video embedded below. It’s a great introduction if you’re new to FM synthesis and want to recreate those magic DOS game sounds.

Of course, you can also just connect the OPL2 chip to your DOS computer, whether through a classic sound card or through a parallel port. The related YM2612 from the Sega Genesis also makes a fine synthesizer.

Continue reading “Recreating The Sounds Of The ’90s With A YM3812 Synthesizer”

A Tiny RISC-V Emulator Runs Linux With No MMU. And Yes, It Runs DOOM!

It’s something of an article of faith, that to run Linux your computer must include a hardware memory management unit, or MMU. To an extent it’s true, in that for a Linux-based system to shine it must have that hardware, but in fact there has been support for MMU-less Linux for many years now. Prolific hacker [cnlohr] has created an emulated simple RISCV processor without an MMU, and not only does it run Linux, it also runs DOOM.

The videos below the break go into significant depth on writing and debugging an emulator not to mention the inner workings of DOOM, but fear not if it’s not your thing. Everything can be found in a GitHub repository, and there are straightforward instructions should you wish to try it yourself.

All this is entertaining stuff, but it becomes of much more interest when viewed as part of an ongoing chain of projects working on no-MMU Linux for low-end RISC-V microcontrollers. Imagine the prospect of running Linux on a CPU costing relative pennies, and you can see why that’s an interesting prospect. Even if it’s not the most unexpected way to run Linux without an MMU.

Continue reading “A Tiny RISC-V Emulator Runs Linux With No MMU. And Yes, It Runs DOOM!”

Transparent Metal (Hydroxide) Without Mr. Scott

There’s a famous scene in one of the Star Trek movies where Scotty, who has traveled to the past, teaches a metal company to create the transparent aluminum he needs to bring some whales back to the future. But [The Action Lab] shows that we already have see-through metal, just not aluminum. You can see a video about why metals are normally opaque.

The metal in question is sodium. Normally, it isn’t transparent, but molten sodium hydroxide does turn transparent after it — well, sort of explodes. Of course, sodium hydroxide isn’t really a metal, but then neither is the aluminum oxide that’s been touted as real transparent aluminum. Aluminum oxide also makes transparent gemstones like rubies. However, there is some — kind of — transparent aluminum at the end of the video.

Continue reading “Transparent Metal (Hydroxide) Without Mr. Scott”

Microscopic Metal 3D Printing With Gels

Everyone wants to 3D print with metals, but it is a difficult task. You need high temperatures and metals with high thermal conductivity make the problem even worse. Researchers at Caltech have a way of printing tiny metal structures. The trick? They don’t print metals at all. Instead, they 3D print a hydrogel and then use it as a scaffold to form metallic structures. You can read the full paper, if you are interested in the details.

Hydrogels are insoluble in water and made from flexible polymer chains. If you’ve ever handled a soft contact lens, that’s a hydrogel. Like resin printing, UV light triggers chemical reactions in the hydrogels, causing them to harden in the desired pattern.

What about the metal? They infuse the hydrogel with a metallic salt dissolved in water.  This saturates the hydrogel. Burning in a furnace causes the hydrogel to burn away but leaves the metal. The furnace also causes the structure to shrink, so this is a good method for very tiny pieces. The team has made prints with feature sizes around 40 microns.

By altering the metal salts, you can work with different metals or even mix different metals. The team has produced parts using copper, nickel, silver, and several alloys.

Printing small structures is a big research goal with many different approaches. We’ve even seen a tiny welder.

Love AI, But Don’t Love It Too Much

The up-and-coming Wonder of the World in software and  information circles , and particularly in those circles who talk about them, is AI. Give a magic machine a lot of stuff, ask it a question, and it will give you a meaningful and useful answer. It will create art, write books, compose music, and generally Change The World As We Know It. All this is genuinely impressive stuff, as anyone who has played with DALL-E will tell you. But it’s important to think about what the technology can and can’t do that’s new so as to not become caught up in the hype, and in doing that I’m immediately drawn to a previous career of mine. Continue reading “Love AI, But Don’t Love It Too Much”

The 10 Kinds Of Programmers That Use Calcutron-33

It is interesting how, if you observe long enough, things tend to be cyclical. Back in the old days, some computers didn’t use binary, they used decimal. This was especially true of made up educational computers like TUTAC or CARDIAC, but there was real decimal hardware out there, too. Then everyone decided that binary made much more sense and now it’s very hard to find a computer that doesn’t use it.

But [Erik] has written a simulator, assembler, and debugger for Calcutron-33, a “decimal RISC” CPU. Why? The idea is to provide a teaching platform to explain assembly language concepts to people who might stumble on binary numbers. Once they understand Calcutron, they can move on to more conventional CPUs with some measure of confidence.

To that end, there are several articles covering the basic architecture, the instruction set, and how to write assembly for the machine. The CPU has much in common with modern microprocessors other than the use of decimal throughout.

There have been several versions of the virtual machine with various improvements and bug fixes. We’ll be honest: we admire the work and its scope. However, if you already know about binary, this might not be your best bet. What’s more is, maybe you should understand binary before tackling assembly language programming, at least in modern times. Still, it does cover a lot of ground that applies regardless.

Made-up computers like TUTAC and CARDIAC were all the rage when computer time was too expensive to waste on mere students. There was also MIX from computer legend Donald Knuth.