A Hundred Year Old Solid State Amplifier

Conventional wisdom has it that the solid state era in electronics began in 1948 with the invention of the transistor, or if you wish to split hairs, with the 1930s invention by the Russian [Oleg Losev] of an early form of tunnel diode. But there’s an earlier amplifier technology that used a solid state circuit which is largely forgotten, and [AWA Communication Technologies Museum] has featured it in a new video. We’re talking of course about the carbon microphone amplifier, a piece of telephone technology which made its way into consumer electronics.

The carbon microphone is a container of loosely packed carbon granules acted upon by a diaphragm. Vibrations from sound compress and decompress the granules, changing the electrical resistance of the carbon. It was the standard microphone used in telephone handsets for most of the twentieth century. Being a resistor it can be placed in a potential divider circuit that produces some significant voltage swings, so when the vibrations come from a high-impedance earpiece it can make an amplifier. It’s not a very good amplifier, it has lousy bandwidth, distortion, and noise characteristics, but it was just about good enough to be paired with a 1920s crystal set. In the video below the break we see a variety of the devices, and even hear them in action sounding very tinny indeed. At the time it must have seemed miraculous to be at the forefront of the new technology though, and we can’t help admiring some of the construction intricacies.

Carbon microphone amplifiers may be rare today, but for all that we’ve touched on them before.

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PI Board chess board on a table in a room

Chess What: One More Pi-Powered Board

Chess is timeless, but automating it? That’s where the real magic begins. Enter [Tamerlan Goglichidze]’s Pi Board, an automated chess system that blends modern tech with age-old strategy. Inspired by Harry Potter’s moving chessboard and the commercial Square Off board, [Tamerlan] re-imagines the concept using a Raspberry Pi, stepper motors, and some clever engineering. It’s not just about moving pieces — it’s about doing so with precision and flair.

At its core, the Pi Board employs an XY stepper motor grid coupled with magnets to glide chess pieces across the board. While electromagnets seemed like a promising start, [Tamerlan] found them impractical due to overheating and polarity-switching issues. Enter servo linear actuators: efficient, precise, and perfect for the job.

But the innovation doesn’t stop there. A custom algorithm maps the 8×8 chess grid, allowing motors to track positions dynamically—no tedious resets required. Knight movements and castling? Handled with creative coding that keeps gameplay seamless. [Tamerlan] explains it all in his sleekly designed build log.

Though it hasn’t been long since we featured a Pi-powered LED chess board, we feel that [Tamerlan]’s build stands out for its ingenuity and optimization. For those still curious, we have a treasure trove of over fifty chess-themed articles from the last decade. So snuggle up during these cold winter months and read up on these evergreens!

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When Transistor Count Mattered

Many Hackaday readers have an interest in retro technology, but we are not the only group who scour the flea markets. Alongside us are the collectors, whose interest is as much cultural as it is technological, and who seek to preserve and amass as many interesting specimens as they can. From this world comes [colectornet], with a video that crosses the bridge between our two communities, examining the so-called transistor wars of the late 1950s and through the ’60s. Just as digital camera makers would with megapixels four or five decades later, makers of transistor radios would cram as many transistors as they could into their products in a game of one-upmanship.

A simple AM transistor radio can be made with surprisingly few components, but for a circuit with a reasonable performance they suggest six transistors to be the optimal number. If we think about it we come up with five and a diode, that’s one for the self-oscillating mixer, one for IF, an audio preamplifier, and two for the audio power amplifier, but it’s possible we’re not factoring in the relatively low gain of a 1950s transistor and they’d need that extra part. In the cut-throat world of late ’50s budget consumer electronics though, any marketing ploy was worth a go. As the price of transistors tumbled but their novelty remained undimmed, manufacturers started creating radios with superfluous extra transistors, even sometimes going as far as to fit transistors which served no purpose. Our curious minds wonder if they bought super-cheap out-of-spec parts to fill those footprints.

The video charts the transistor wars in detail, showing us a feast of tiny radios, and culminating in models which claim a barely credible sixteen transistors. In a time when far more capable radios use a fraction of the board space, the video below the break makes for a fascinating watch.

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Your Undocumented Project May Also Baffle People Someday

What’s life without a little mystery? There’s one less rolling around after historians finally identified a donated mystery machine that had been in storage for years.

Feeding dough through this machine may have been faster, but probably not safer.

The main pieces of the machine are about a century old and any staff who may have known more about the undocumented device were no longer around to ask. The historical society finally posted pictures and asked for any insights, which eventually led to solving the mystery.

The machine is in all likelihood a beaten biscuit maker, which was a type of dense baked good popular in the American south. Making them called for a long and labor-intensive process of pounding and working the dough, and the society says this machine was likely created by a fellow trying to help his aunt streamline her business, offloading the labor of working the dough to a machine.

The machine had no branding of any sort and lacked any identifying marks. Its purpose was doubtlessly obvious at the time, but no records remained and quite possibly none existed in the first place. Sound familiar? Perhaps someday our own undocumented projects and prototypes will mystify people. It’s certainly happened in the case of mysterious Roman dodecahedrons, which remain a head-scratching mystery.

Vintage telephone

World’s First Virtual Meeting: 5,100 Engineers Phoned In

Would you believe that the first large-scale virtual meeting happened as early as 1916? More than a century before Zoom meetings became just another weekday burden, the American Institute of Electrical Engineers (AIEE) pulled off an unprecedented feat: connecting 5,100 engineers across eight cities through an elaborate telephone network. Intrigued? The IEEE, the successor of the AIEE, just published an article about it.

This epic event stretched telephone lines over 6,500 km, using 150,000 poles and 5,000 switches, linking major hubs like Atlanta, Boston, Chicago, and San Francisco. John J. Carty banged the gavel at 8:30 p.m., kicking off a meeting in which engineers listened in through seat-mounted receivers—no buffering or “Can you hear me?” moments. Even President Woodrow Wilson joined, sending a congratulatory telegram. The meeting featured “breakout sessions” with local guest speakers, and attendees in muted cities like Denver sent telegrams, old-school Zoom chat style.

The event included musical interludes with phonograph recordings of patriotic tunes—imagine today’s hold music, but gloriously vintage. Despite its success, this wonder of early engineering vanished from regular practice until our modern virtual meetings.

We wonder if Isaac Asimov knew about this when he wrote about 3D teleconferencing in 1953. If you find yourself in many virtual meetings, consider a one-way mirror.

Retrogadgets: Oscilloscope Cameras

Today, if you want to get a picture from your oscilloscope — maybe to send to a collaborator or to stick in a document or blog post — it is super easy. You can push an image to a USB stick or sometimes even just use the scope’s PC or web interface to save the picture directly to your computer. Of course, if it is on the computer, you could use normal screen capture software. But that hasn’t always been the case. Back in the days when scopes were heavy and expensive, if you wanted to capture an image from the tube, you took a picture. While you might be able to hold up your camera to the screen, they made specific cameras just for this purpose.

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Building A DIY Nipkow Disk Display

Before flat screen technologies took over, we associate TV with the CRT. But there were other display technologies that worked, they just weren’t as practical. One scheme was the Nipkow disk, and [Bitluni] decided to build a working demonstration of how such a system works.

Essentially, there’s a spinning disk with a spiral pattern of holes in it. As the disk spins, a light behind it turns on or off. If you time everything right, you get an image that can move. This particular model uses stepper motors, which is a bit of a modern concession.

The result was actually much better than you might guess, but a far cry from a modern display device, of course. The screen material needed a little tweaking, but even the initial results were very impressive. If this were trying to be practical, it would probably require a bit more work on the light source and screen.

Interestingly, the Nipkow disk arrangement was just as suitable for scanning as displaying. Instead of a light behind the wheel, you simply used a light sensor. Of course, in practice, getting everything synchronized and mass-producing high-resolution sets would have been a tremendous challenge a century ago.

Not that people didn’t try. There were even color systems using mechanical wheels. In the 1930s, people were sure your TV would contain spinning disks.

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