Author: Jenny List

3081 Articles

Bringing A Current Dumping Amplifier Back To Life

February 27, 2025 by 9 Comments

Over the years there have been many different audio amplifier designs which have found favour for a while and then been supplanted by newer ideas. One of them has crossed the bench of [Jazzy Jane], it’s a current dumping amplifier from the mid-1980s. A nicely-done home-made project on stripboard mounted on a wooden base board, it sports a power supply, RIAA pre-amp board, and the amplifier itself.

The current dumping amplifier is one that combines a small class A amplifier with a hefty class B one, and through feedback trickery uses the combination to remove the crossover distortion of the class B stage. It’s a simple yet elegant circuit with fewer parts than an equivalent class AB amplifier, and there was a time back in the day when it was all the rage. This one has an op-amp providing the class A part and a complimentary pair of Darlington pairs as the class B.

The video below the break shows the process of bringing the amp back to life, a process mostly concerned with the power supply. There are a set of tantalum capacitors which have failed, and the replacements she’s using turn out to have problems too. They’re a period part for a project of this age, but we might have been tempted to go for another capacitor type here.

The result is an unusual amplifier, brought back to life. You may have seen [Jane] feature here before, with her 1950s signal generator.

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SHOUT For Smaller QR Codes

February 26, 2025 by 19 Comments

QR codes have been with us for a long time now, and after passing through their Gardenesque hype cycle of inappropriate usage, have now settled down to be an important and ubiquitous part of life. If you have ever made a QR code you’ll know all about trying to generate the most compact and easily-scannable one you can, and for that [Terence Eden] is here with an interesting quirk. Upper-case text produces smaller codes than lower-case.

His post takes us on a journey into the encoding of QR codes, not in terms of their optical pattern generation, but instead the bit stream they contain. There are different modes to denote different types of payload, and in his two examples of the same URL in upper- and lower- cases, the modes are different. Upper-case is encoded as alphanumeric, while lower-case, seemingly though also containing alphanumeric information, is encoded as bytes.

To understand why, it’s necessary to consider the QR codes’ need for efficiency, which led its designers to reduce their character set as far as possible and only define uppercase letters in their alphanumeric set. The upper-case payload is thus encoded using less bits per character than the lower-case one, which is encoded as 8-bit bytes. A satisfying explanation for a puzzle in plain sight.

Hungry for more QR hackery? This one contains more than one payload!

A Ten Band SDR Transceiver For Homebrewers

February 26, 2025 by 9 Comments

Making a multi-band amateur radio transceiver has always been a somewhat challenging project, and making one that also supported different modes would for many years have been of almost impossible complexity best reserved for expensive commercial projects. [Bob W7PUA] has tackled both in the form of a portable 10-band multi-mode unit, and we can honestly say he’s done a very good job indeed.

As you might expect in 2025 it’s a software defined radio (SDR), but to show how powerful the silicon available today is, it’s all implemented on a microcontroller. There’s a Teensy 4 with an audio codec board that does all the signal processing heavy lifting, and an RF board that takes care of the I/Q mixing and the analogue stuff.

Band switching is handled using a technique from the past; interchangeable plug-in coil and filter units, that do an effective job. The result is a modestly-powered but extremely portable rig that doesn’t look to have broken the bank, and since the write-up goes into detail on the software side we hope it might inform other SDR projects too. We might have gone for old-school embossed Dymo labels on that brushed aluminium case just for retro appeal, but we can’t fault it.

It’s not the first time we’ve looked at a small multi-band SDR here, but we think this one ups the game somewhat.

Thanks [Pete] for the tip!

BlackBerry Keyboard Makes This Handheld Pi Stand Out

February 25, 2025 by 14 Comments

In the decade or more since small inexpensive Linux-capable single board computers such as the Raspberry Pi came to the mainstream, many a hardware hacker has turned their attention to making a portable computer using one. With such a plethora of devices having been made one might think that the Pi handheld was a done deal, but every so often along comes a new one of such quality to re-ignite the genre. So it is with [Taylor Hay]’s BlackberryPi Handheld. As you might guess from the name, it uses a BlackBerry keyboard along with a square LCD screen to create a beautifully executed Pi handheld in an almost GameBoy-like form factor.

It starts with a beautifully designed and executed case that holds a Pi and a Pimoroni HyperPixel screen. Unexpectedly this is a full-size Pi, we think a Pi 4. The keyboard is a USB enhanced Blackberry module which also has the famous trackpad, and there’s a bezel on the front to protect the screen. The power meanwhile comes from three 18650 cells inside the back of the case, with a power bank PCB. The surprise here is how simple he’s made it by careful choice of modules, the usual rats-nest of wires is missing.

The files are available so you can make your own, and he’s actively encouraging people to remix and improve it. We like this project, a lot, and after you’ve seen the video below the break, we think you will too. Oddly, this isn’t the first time we’ve seen someone try this combination.

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3D Print An Instant Camera

February 24, 2025 by 8 Comments

Instant photography occupies a niche in film photography that has endured despite its relatively high cost and the ease of newer digital technologies. There are two main manufacturers, Polaroid and Fujifilm, as well as a few smaller boutique camera makers. Into this comes [Toast], with an entirely 3D printed instant camera, not a Polaroid as he calls it, but one for Fuji Instax Mini film.

Currently available instant film comes in cartridges in which each picture is a layered design with a sachet of developing chemicals at the end. Once the film part has been exposed it is developed by passing through a set of rollers which squeeze the chemicals evenly over the film, allowing it to develop. The camera in the video below the break is simple enough, a pinhole box camera design, but the huge challenge and the interesting part of the video comes in the developer attachment which has those rollers. It’s considerably more challenging than it might at first appear, and he goes through many iterations before getting it right with some steel rollers.

The 3D print files are available but only at a price, and despite that we think there’s enough in the video below for anyone who wants to experiment for themselves. For the rest of us it’s an insight into a technology we all know about, but maybe have never looked closely at.

Instax has appeared here before, usually as an instant back for older cameras, but sometimes for far tastier projects.

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Old IPad To New Screen

February 24, 2025 by 5 Comments

Turning surplus LCD panels into stand-alone monitors with the help of a driver board is an established hack, and a search of eBay or AliExpress will turn up boards for almost any widely available panel. [Drygol] has a couple of old iPad screens, and has done exactly this with them. What makes these two projects stand aside from the crowd is their attention to detail, instead of creating a hacky monitor this is almost something you might buy as a product.

For a start, both screens sit in very smart 3D printed cases. Behind them is the LCD driver, and perhaps this is where many people might leave it. But the point of an iPad is portability, so the first one receives a suitably large lithium polymer battery and its associated electronics. As such a thing is of limited use without a battery level monitor, so one is mounted flush with the case on the outside. The final touch is a Bluetooth audio board and speaker, making an all-in-one peripheral we’d be happy to carry with us.

The second screen is a slimmer version of the first case, with a different board that has an onboard audio channel. It’s mounted in a stand with a MiSter FPGA emulator, for a very neat and compact desktop set-up.

This project shows what can be done with these screens, and raises the bar. All the files are included, so it should be possible to make your own. We expect someone might stick a Raspberry Pi in there, to make… something like an iPad.

This isn’t the first time we’ve seen an iPad screen mod.

UNIX Archaeology Turns Up 1972 “V2 Beta”

February 20, 2025 by 20 Comments

In 1997 a set of DEC tapes were provided by Dennis Ritchie, as historical artifacts for those interested in the gestation of the UNIX operating system. The resulting archive files have recently been analysed by [Yfeng Gao], who has succeeded in recovering a working UNIX version from 1972. What makes it particularly interesting is that this is not a released version, instead it’s a work in progress sitting somewhere between versions 1 and 2. He’s therefore taken the liberty of naming it “V2 Beta”.

If you happen to have a PDP-11/20 you should be able to run this operating system for yourself, and for those of us without he’s provided information on which emulator will work. The interesting information for us comes in the README accompanying the tapes themselves, and in those accompanying the analysis. Aside from file fragments left over from previous users of the same tape, we learn about the state of UNIX time in 1972. This dates from the period when increments were in sixtieths of a second due to the ease of using the mains power frequency in a PDP, so with a 32-bit counter they were facing imminent roll-over. The 1970-01-01 epoch and one second increments would be adopted later in the year, but meanwhile this is an unusual curio.

If you manage to run this OS, and especially if you find anything further in the files, we’d love to hear. Meanwhile, this is not the oldest UNIX out there.

Featured image: “PDP-11/20 Rocker Switches” by Don DeBold