A Tube Tester Laid Bare

February 8, 2024 by Jenny List 13 Comments

There’s still a mystique around vacuum tubes long after they were rendered obsolete by solid state devices, and many continue to experiment with them. They can be bought new, but most of us still come to them through the countless old tubes that still litter our junk boxes. But how to know whether your find is any good? [Rob’s Fixit Shop] took a look at a tube tester, once a fairly ubiquitous item, but now a rare sight.

To look at it’s a box with an array of tube sockets, a meter, and a set of switches to set the pinout for the tube under test. We expected it to use a common-cathode circuit, but instead it measures leakage between the grid and the other electrodes, a measure of how good the vacuum in the device is. In a worrying turn this instrument can deliver an electric shock, something he traces to a faulty indicator light leading to the chassis. We are however still inclined to see it as anything but safe, because the lack of mains isolation still exposes the grid to unwary fingers.

All in all though it’s an interesting introduction to an unusual instrument, and given a suitable isolating transformer we wouldn’t mind the chance to have one ourselves. If you need to test a tube and don’t have one of these, don’t worry. It’s possible to roll your own.

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Revisiting A Z80 Game From 1990

February 8, 2024 by Jenny List 16 Comments

Back in the days of 8-bit computers, like no doubt many readers of similar age, we wrote little games. First in BASIC, then augmented with little machine code speed-ups. We didn’t come close to [Óscar Toledo Gutiérrez] though, who’s reverse engineering a 2K all-machine-code game he wrote back in 1990. As a tale of software archaeology it’s fascinating.

The game itself is an avoid-the-monsters platformer with plenty of ladders for the little sprite-based protagonist to run down. The computer was a Mexican homebrew educational machine with a TMS9118 display chip and an AY-3-8910 synthesizer, so the result had both color and music. His run through the code breaks it down neatly into individual sections, so it’s possible to see what’s going on without an in-depth knowledge of machine code.

He readily admits it bears all the hallmarks of an 11-year-old’s knowledge at the time, and that it has some parts less elegant, but nevertheless it’s something of an achievement at any age. It was out of date gameplay-wise in 1990 but in 1982 it could probably have been bought on a tape by eager kids. Here in 2024 he’s got it for download should you have a Colecovision or an MSX. There’s a gameplay video below the break, take a look.

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Schematics, For A Modern Flagship Phone

February 7, 2024 by Jenny List 36 Comments

The mobile phone is an expensive and often surprisingly fragile device, whose manufacturers are notorious for making them as difficult to repair as possible. Glued-together cases and unreplaceable batteries abound, and technical information is non-existent. But amongst all that there’s one manufacturer with a different approach — Fairphone. Case in point, they’ve released the full service guide including schematics for their flagship Fairphone 5.

Fairphone’s selling point is the repairability and internal accessibility of their products and of course they’ve made hay with this as a marketing opportunity. But aside from that, it’s a fascinating chance to look in-depth at a modern smartphone from the inside out. We see the next-level PCB layout and how everything is so neatly packed into the minimum space, all without resorting to a heat gun.

It’s great to have another hackable phone, and fair play to Fairphone for releasing all this stuff, but perhaps the most interesting part from where we’re sitting is how and where this phone is being sold. There have been hackable phones before, for many the Pinephone will spring to mind, but they have always been sold to an audience who buy to hack. Here in Europe where this is being written, the Fairphone is being sold as a consumer device. It won’t shake Apple or Samsung from their perches, but for a hackable device to be so generally available to those who wish to do things with it can never be a bad thing.

We took a quick look at Fairphone back in 2015, when they launched.

It Wasn’t DOOM That Killed The Amiga

February 6, 2024 by Jenny List 117 Comments

If you were the type of person who might have read Hackaday had we been around in the late 1980s or early 1990s, it’s a reasonable guess that you would have had a 16-bit home computer on your desk, and furthermore that it might have been a Commodore Amiga. These machines gave the best bang for the buck in those days with their impressive multimedia capabilities, and they gained a fervent following which persists to this day. [Carl Svensson] was one of them, and he’s penned a retrospective on the demise of the platform with the benefit of much hindsight.

The heyday of the Amiga from its 1985 launch until the days of the A1200 in the early-to-mid 1990s saw Moore’s Law show perhaps its fastest effects for the consumer. In that decade the PC world jumped from the 8088 to the Pentium, and from a PC speaker and CGA if you were lucky, to a Sound Blaster 16 and accelerated SVGA. By comparison the Amiga didn’t change much except in model numbers and a few extra graphics modes, and when a faster processor came it was far to little too late.

*Defender of the Crown*, released in 1986

There’s a well-worn path with some justification of blaming Commodore-s notoriously awful management for the debacle, but the piece goes beyond that into the mid ’90s. His conclusion is that what really killed the Amiga was that the CPU price reductions which defined the x86 world at that time never came to 68k or PowerPC lines, and that along with the architecture zealotry of the fan base meant that there would never be the much-longed-for revival.

He also takes a look at the other home computer platforms of the era, including the “all its killer architecture managed to kill was, sadly, Atari itself” Atari Falcon, and the Acorn Archimedes, which also lives on for enthusiasts and is perhaps the most accessible survivor. From here having also the benefit of hindsight we can’t disagree with him on his assessment, so perhaps it’s best to look at the Amiga not as the platform we should rightfully still be using, but the great stepping stone which provided us a useful computer back in t he day without breaking the bank.

An Apple ][ With A Pendulum

February 5, 2024 by Jenny List 6 Comments

Clocks are a favourite project here, and we can say we’ve seen all conceivable types over the years. Just a software clock on a retrocomputer perhaps isn’t the coolest among them, but [Willem van der Jagt ]’s Apple][ clock has a little bit extra. It takes its time reference from a real pendulum, on an antique wall clock.

A proximity sensor next to a metal pendulum gives an easy way to generate a digital pulse on each pass, but leaves the question of how to transfer it to the computer. With computers of this age the circuitry is surprisingly simple, and in this case he’s sending an interrupt to the machine which the software can pick up for its timing. There is a small logic circuit between the sensor and the interrupt allowing him to gate the pendulum line, triggered from one of the output lines exposed on the Apple’s game port.

The code is written in assembly, and counts the number of pendulum swings before incrementing the number of minutes. It’s an enjoyable reminder of the days when the architecture of a computer was this accessible, and for those of us whose past lies in the Sinclair world it’s also been a little peek into something of how the Apple works.

We think this is the first pendulum-driven retrocomputer clock we’ve seen here at Hackaday, as you might understand when a clock has a pendulum it’s usually a more traditional design.

A Crossbar Telephone Switch Explained

February 4, 2024 by Jenny List 14 Comments

There’s an old adage about waiting hours for a bus only for two to appear at once, and for Hackaday this month we’re pleased to have seen this in a run of analogue telephone projects. Latest among them is the video below the break from [Wim de Kinderen], who is demonstrating the workings of a mechanical crossbar switch with the help of a vintage Ericsson unit and an Arduino replacing the original’s bank of control relays.

It’s possible everyone has a hazy idea of a crossbar array, but it was fascinating from this video to learn that the relays are worked by metal fingers being inserted by the bars into relays with wider than normal gaps between electromagnet and armature. This extra metal provides a path for the magnetic flux to actuate the relay.

The machine itself then is an extremely simple and elegant electromechanical device with many fewer moving parts than its Strowger rotary equivalents, but surprisingly we seem to see less of it than its American competitor. The video below the break is definitely worth a watch, even if you don’t own any analogue phones.

We recently saw a similar exchange implemented electronically.

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Why Not Try A DIAC?

February 3, 2024 by Jenny List 31 Comments

There are plenty of electronic components which were once ubiquitous but once the niche which led to their existence has passed, they fade away to remain a junkbox curio. The DIAC is the subject of a recent ElectronicsNotes video, and while it might not quite yet have slid into total obscurity yet it’s definitely not the most common of parts in 2023.

If you’ve encountered one it will almost certainly be in the trigger circuit of a lighting dimmer or motor controller, where its bidirectional breakover makes for symmetrical control of a triac gate. This extremely simple circuit allows for perfect control of AC-powered devices, and could once be found everywhere. Its demise over recent years tells an interesting story of our changing use of electricity, as not only have other devices such as smart lights and brushless motors appeared which preclude traditional dimmers, but also we now demand better RF performance from our lighting controls.

The DIAC is still a handy part to know about, and you can take a look at the video below the break. We would normally try to link to another Hackaday story using a DIAC, but is it telling that we couldn’t find one? If you can, link it in the comments!

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