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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Resistor Color Code Clock Is A Bit Of Fun

February 3, 2024 by Jenny List 6 Comments

Younger electronic engineers may see resistors with old-style color codes to display their values a little less than those from previous years, but if there’s a shibboleth among those who wield a soldering iron it’s probably something similar to instinctively saying “1K” when asked “Brown-black-red?”. Colors as numbers can be used outside resistors, for example in a clock, as [Det Builds Stuff] shows us with an ESP32 TFT dev board.

It’s fair to say that this is more of a software project than a hardware one, but that’s not necessarily a bad thing as he takes us though the process of creating a Network Time Protocol (NTP) capable clock with the dev board. He claims it may be the world’s first resistor clock, something we’d have to disagree with, but beside that we can see this could make a neat little desk ornament with a 3D printed case.

Oddly though, we’d expect older engineers to face the same steep learning curve as younger ones when reading it, because it’s easier to recognize visual sequences of numbers as preferred resistor values than it is to visually decode each one every time.

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Your Surface RT Can Become Useful Again, With Raspberry Pi OS

February 2, 2024 by Jenny List 20 Comments

Over the years there have been so many times when Microsoft came up with a product that so nearly got it right, but which tanked in the market because the folks at Redmond had more of an eye to what fitted their strategy than what the customer wanted. The Surface RT was one of these: while the hardware was at least as good if not better than Apple’s iPad, its ARM CPU and an ill-advised signed-apps-only policy meant the tablet couldn’t access the huge existing library of Windows software.

Consumers didn’t want a tablet with next-to-no apps, so it failed miserably. Never mind though, because [Michael MJD] has a video showing how an RT can be given a new life from an unlikely source, with the installation of Raspberry Pi OS.

The video pretty closely follows this guide, and involves creating a Raspberry Pi OS install medium modified with RT-specific kernel modules and device tree. It’s possible because the 32-bit ARM architecture is one of those which Raspberry Pi OS targets, and while a few things such as graphics acceleration don’t work, it’s still successful (if a little slow).

Oddly this is a technique not unlike one from the earliest days of the Raspberry Pi, when we remember people in Raspberry Pi Jams showing off the ancestor of the modern OS running on cheap ARM-based netbooks. In those cases the hack relied on transplanting the Pi userland over the device’s existing kernel, we’d be interested in an explanation of how the RT can use the Pi kernel without the famous Broadcom BLOB intended for the Pi.

We have a soft spot for the RT, as we said a good product held back by a very bad software decision. Seeing it take a new life years later is thus pleasing to us.

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Will There Be Any Pi Left For Us?

February 2, 2024 by Jenny List 72 Comments

Our world has been abuzz with the news that Raspberry Pi are to float on the London Stock Exchange. It seems an obvious move for a successful and ambitious company, and as they seem to be in transition from a maker of small computers into a maker of chips which happen to also go on their small computers, they will no doubt be using the float to generate the required investment to complete that process.

New Silicon Needs Lots Of Cash

An RP1 chip on a Raspberry Pi 5. — The most important product Raspberry Pi have ever made.

When a tech startup with immense goodwill grows in this way, there’s always a worry that it could mark the start of the decline. You might for instance be concerned that a floated Raspberry Pi could bring in financial whiz-kids who let the hobbyist products wither on the vine as they license the brand here and there and perform all sorts of financial trickery in search of shareholder value and not much else. Fortunately we don’t think that this will be the case, and Eben Upton has gone to great lengths to reassure the world that his diminutive computers are safe. That is however not to say that there might be pitfalls ahead from a hobbyist Pi customer perspective, so it’s worth examining what this could mean.

As we remarked last year, the move into silicon is probably the most important part of the Pi strategy for the 2020s. The RP2040 microcontroller was the right chip with the right inventory to do well from the pandemic shortages, and on the SBCs the RP1 all-in-one peripheral gives them independence from a CPU house such as Broadcom. It’s not a difficult prediction that they will proceed further into silicon, and it wouldn’t surprise us to see a future RP chip containing a fully-fledged SoC and GPU. Compared to their many competitors who rely on phone and tablet SoCs, this would give the Pi boards a crucial edge in terms of supply chain, and control over the software.

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Multi-way Capacitor Replacement Without The Pain

February 1, 2024 by Jenny List 20 Comments

Anyone who’s worked with older tube-based equipment will be familiar with the type of vintage electrolytic capacitor which integrated several capacitors into one can. Long obsolete, they can be bought as reproduction, but unfortunately at an eye-watering price. [D-Lab Electronics] introduces us to a solution using a very useful kit, that it’s worth sharing.

The piece of equipment in the video below the break is a rather lovely Heathkit oscillator, following the familiar phase shift model with a light bulb in its feedback loop. It’s a piece of test equipment that produces a low-distortion sine wave output, and would still be of use to an audio engineer today. He replaces the capacitor with two modern ones on a multi-cap board from [W8AOR], who sells a variety of these kits for different configurations.

We’ve done this very repair more than once, and it has usually involved wiring, heatshrink sleeving, hot glue, and cable ties, looking very messy indeed. It’s not that often that a kit catches our eye as this one has, but we know we’ll be finding it useful here some time in the future. Meanwhile if you’d like to know why this oscillator has a light bulb, take a look at our piece on distortion.

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This Time It’s Toyota: Takata Airbag Recalls Continue

February 1, 2024 by Jenny List 22 Comments

The automotive industry is subject to frequent product recalls, as manufacturers correct defects in their vehicles that reveal themselves only after some use. While such events may be embarrassing for a marque, it’s not necessarily a bad thing — after all, we would rather put our trust in a carmaker prepared to own up and fix things rather than sweep their woes under the carpet.

There’s one recall that’s been going on for years which isn’t the vehicle manufacturer’s fault though, and now it seems Toyota are the latest to be hit, with some vehicles as old as two decades being part of it. Long time Hackaday readers will probably recognize where this is going as we’ve covered it before; at its centre are faulty airbag charges from Takata, and the result has been one of the largest safety related recalls in automotive history.

An automotive airbag is a fabric structure inflated at high speed by a small explosive charge when triggered by the sharp deceleration of an incident. It is intended to cushion any impact the occupant might make upon the car’s interior. The problem with the faulty Takata units is that moisture ingress could alter the properties of the charge, and this along with corrosion could increase its power and produce a hail of metal fragments on detonation.

Our colleague [Lewin Day] has penned a series of informative and insightful investigations of the technology behind the Takata scandal, going back quite a few years. With such relatively ancient vehicles now being recalled we can’t help wondering whether it would be easier for Toyota to run a buyback scheme and take the cars off the road rather than fix them in this case, but we’re curious as non automotive safety engineers why the automotive airbag has evolved in this manner. Why is one of very few consumer explosive devices not better regulated, why is it sold with an unlimited lifetime, and why are they not standardized for routine replacement on a regular schedule just like any other vehicle consumable?

2003-2004 Toyota Corolla: IFCAR, Public domain.