Custom Isolated Variac Is Truly One Of A Kind

It’s no surprise that many hardware hackers avoid working with AC, and frankly, we can’t blame them. The potential consequences of making a mistake when working with mains voltages are far greater than anything that can happen when you’re fiddling with a 3.3 V circuit. But if you do ever find yourself leaning towards the sparky side, you’d be wise to outfit your bench with the appropriate equipment.

Take for example this absolutely gorgeous variable isolation transformer built by [Lajt]. It might look like a  high-end piece of professional test equipment, but as the extensive write-up and build photographs can attest, this is a completely custom job. The downside is that this particular machine will probably never be duplicated, especially given the fact its isolation transformer was built on commission by a local company, but at least we can look at it and dream.

This device combines two functions which are particularly useful when repairing or testing AC hardware. As a variable transformer, often referred to as a variac, it lets [Lajt] select how much voltage is passed through to the output side. There’s a school of thought that says slowly ramping up the voltage when testing an older or potentially damaged device is better than simply plugging it into the wall and hoping for the best. Or if you’re like Eddie Van Halen, you can use it to control the volume of your over-sized Marshall amplifiers when playing in bars.

Image of the device's internal components.Secondly, the unit isolates the output side. That way if you manage to cross the wrong wire, you’re not going to pop a breaker and plunge your workshop into darkness. It also prevents you from accidentally blowing up any AC powered test equipment you might employ while poking around, such as that expensive oscilloscope, since the devices won’t share a common ground.

Additional safety features have been implemented using an Arduino Uno R3 clone, a current sensor, and several relays. The system will automatically cut off power to the device under test should the current hit a predetermined threshold, and will refuse to re-enable the main relay until the issue has been resolved. The code has been written in such a way that whenever the user makes a configuration change, power will be cut and must be reestablished manually; giving the user ample time to decide if its really what they want to do.

[Lajt] makes it clear that the write-up isn’t meant as a tutorial for building your own, but that shouldn’t stop you from reading through it and getting some ideas. Whether you’re in the market for custom variac tips or just want to get inspired by an impeccably well engineered piece of equipment, this project is a high-water mark for sure.

Vintage Test Equipment Addiction Justified

Recore 3D printer board developer [Elias Bakken] has posted about the automatic test procedure he developed using a stack-up of four (at least) pieces of vintage HP test equipment. In addition, his test jig and test philosophy is quite interesting.

Besides making a bed-of-nails test jig, he also designed a relay multiplexing board to that selects one of the 23 different voltages for measurement. We like his selection of mechanically latching relays in this application — not only does it save power, but it doesn’t subject the test board to any magnetic fields (except when switching state).

In [Elias]’s setup, the unit under test (UUT) actually orchestrates the testing process itself. This isn’t as crazy as it might sound. The processor is highly integrated in one package plus external DRAM. If the CPUs boot up at all, and pass simple self-test routines, there’s no reason not to utilize the on-board processor as the main test control computer. This might be a questionable decision if your processor was really small with constrained resources and connectivity. But in the case of Recore, the processor is a four-core ARM A53 SoC running Debian Linux — an arrangement that itself could well serve as an automated test computer in other projects.

In the video down below, [Elias] walks us through the basic tests, and then focuses on the heart of the Recore board tests: calibrating the input signal conditioning circuits. Instead of using very expensive precision resistors, [Elias] selected more economical 1% resistors to use in the preamp circuitry. The tradeoff here is the need to calibrate each channel, perhaps at multiple temperature points. This is a situation where using a test jig, automated test scripts, and and stack of programmable test equipment really shines.

[Elias] is still pondering some issues he found trying to calibrate thermocouples, so his adventure is not quite over yet. If you are wondering what Recore is, check out this article from back in June. Have you ever used the microprocessor on a circuit board to test itself, either standalone or in conjunction with an external jig? Let us know in the comments below.

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Boat Anchor Nixie Clock Plays The Cold Warrior Role Convincingly

The early Cold War years may have been suffused with existential dread thanks to the never-ending threat of nuclear obliteration, but at least it did have a great look. Think cars with a ton of chrome, sheet steel toys with razor-sharp edges, and pretty much the entire look of the Fallout franchise. And now you can add in this boat anchor of an electromechanical Nixie clock, too.

If [Teti]’s project looks familiar, perhaps it’s because the build was meant as an homage to the test equipment of yore, particularly some of the sturdier offerings from Hewlett-Packard. But this isn’t some thrift store find that has been repurposed; rather, the entire thing, from the electronics to the enclosure, is scratch built. The clock circuit is based on 4000-series CMOS chips and the display uses six IN-1 Nixies. Instead of transistors to drive the tubes, [Teti] chose to use relays, which in the video below prove to be satisfyingly clicky and relaxing. Not relaxing in any way is the obnoxious alarm, which would be enough to rouse a mission control officer dozing in his bunker. [Teti] has a blog with more details on the build, the gem of which is information on how he had the front panel so beautifully made.

We can’t say enough about the fit and finish of this one, as well as the functionality. What’s even more impressive is that this was reportedly [Teti]’s first project like this. It really puts us in mind of some of the great 6502 retrocomputer builds we’ve been seeing lately.

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Hackaday Links: March 7, 2021

It’s March, which means Keysight is back in the business of giving away a ton of test gear. Keysight University Live starts on March 15, with daily events the first week followed by a string of weekly live events through April. We always enjoy these Keysight events; sure, they’re clearly intended to sell more gear, but the demos and tutorials are great, and we always learn a lot. There’s also a feeling of community that feels similar to the Hackaday community; just a bunch of electronics nerds getting together to learn and share. If you’re interested in that community, or even if you’re just looking for a chance to win something from the $300,000 pile of goodies, you’ll need to register.

There’s another event coming up that you’ll want to know about: the 2021 Open Hardware Summit. Because 2021 is the new 2020, the summit is being held virtually again, this year on April 9. Tickets are on sale now, and we’re told there are still plenty of Ada Lovelace Fellowships available to those who consider themselves to be a minority in tech. The Fellowship covers the full cost of a ticket; it usually covers travels costs too, but sadly we’re still not there yet.

Once we do start traveling again, you might need to plan more carefully if cities start following the lead of Petaluma, California and start banning the construction of gas stations. The city, about 40 miles (64 km) north of San Francisco, is believed to be the first city in the United States to ban new gas station construction. The city council’s decision also prevents gas station owners from expanding, reconstructing, or relocating existing gas stations. The idea is to create incentives to move toward non-fossil fuel stations, like electric vehicle charging stations and hydrogen fueling. Time will tell how well that works out.

Go home Roomba — you’re drunk. That could be what Roomba owners are saying after an update semi-bricked certain models of the robotic vacuum cleaners. Owners noted a variety of behaviors, like wandering around in circles, bumping into furniture, and inability to make its way back to base for charging. There’s even a timelapse on reddit of a Roomba flailing about pathetically in a suspiciously large and empty room. The drunken analogy only goes so far, though, since we haven’t seen any reports of a Roomba barfing up the contents of its dust bin. But we’re still holding out hope.

And finally, if you’re not exactly astronaut material but still covet a trip to space, you might luck out courtesy of Japanese billionaire Yusaku Maezawa. He’s offering to pay the way for eight people from around the world on a planned flight to the Moon and back in 2023. Apparently, Maezawa bought up all the seats for the flight back in 2018 with the intention of flying a group of artists to space. His thinking has changed, though, and now he’s opening up the chance to serve as ballast join the crew to pretty much any rando on the planet. Giving away rides on Starship might be a harder sell after this week’s test, but we’re sure he’ll find plenty of takers. And to be honest, we wish the effort well — the age of routine civilian space travel can’t come soon enough for us.

Logic Meter Aims To Make Hobby Electronics Troubleshooting Easier

The basic test instrument suite — a bench power supply, a good multimeter and perhaps an oscilloscope — is extremely flexible, but not exactly “plug and play” when it comes to diagnosing problems with some common hardware setups. A problem with a servo driver, for example, might be easy enough to sort of with a scope, but setting everything up to see what’s going on with the PWM signal takes some time.

There’s got to be a better way to diagnose hobby electronics woes, and if [Bob Alexander] has his way, his “Logic Meter”, or something very close to it, will be the next must-have bench tool. The Logic Meter combines some of the functionality of an oscilloscope and a logic analyzer into a handy instrument that’s as easy to use as a multimeter. The Logic Meter’s probes connect to logic-level signals in a circuit and can be set up to capture or send serial data, either directly to or from a UART or via an SPI bus connection. There are also functions for testing servos and similar devices with a configurable PWM output. [Bob] rounds out the functionality with a GPS simulator and a simple logic analyzer, plus some utility functions.

The beauty part of the Logic Meter is that [Bob] has left where it goes next largely up to the community. He’s got a GitHub repo with details on the PIC32-based hardware, and the video below makes it clear that this is just a jumping-off point to further work that he hopes results in a commercial version of the Logic Meter. That’s a refreshing attitude, and we hope it pays off; from the look of a few of [Bob]’s retrocomputing makeovers, something like the Logic Meter could come in pretty handy.

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Blue Pill As A Nerdy Swiss Army Knife

Not everyone can afford an oscilloscope, and some of us can’t find a USB logic analyzer half the time. But we can usually get our hands on a microcontroller kit, which can be turned into a makeshift instrument if given the appropriate code. A perfect example is buck50 developed by [Mark Rubin], an open source firmware to turn a STM32 “Blue Pill” into a multi-purpose test and measurement instrument.

buck50 comes with a plethora of functionality built in which includes an oscilloscope, logic analyzer, and bus monitor. The device is a two way street and also comes with GPIO control as well as PWM output. There’s really a remarkable amount of functionality crammed into the project. [Mark] provides a Python application that exposes a text based UI for configuring and using the device though commands and lots of commands which makes this really nerdy. There are a number of options to visualize the data captured which includes gnuplot, gtk wave and PulseView to name a few.

[Mark] does a fantastic job not only with the firmware but also with the documentation, and we really think this makes the project stand out. Commands are well documented and everything is available on [GitHub] for your hacking pleasure. And if you are about to order a Blue Pill online, you might want to check out the nitty-gritty of the clones that are floating around.

Thanks [JohnU] for the tip!

Custom Electronic Load Makes Use Of Gaming PC Tech

At first glance, you might think the piece of hardware pictured here is a modern gaming computer. It’s got water cooling, RGB LED lighting, and an ATX power supply, all of which happen to be mounted inside a flashy computer case complete with a clear window. In truth, it’s hard to see it as anything but a gaming PC.

In actuality, it’s an incredible custom electronic load that [EE for Everyone] has been developing over the last four months that’s been specifically designed to take advantage of all the cheap hardware out there intended for high-performance computers. After all, why scratch build a water cooling system or enclosure when there’s such a wide array of ready-made ones available online?

The “motherboard” with single load module installed.

Inside that fancy case is a large PCB taking the place of the original motherboard, to which four electronic load modules slot into. Each of these loads is designed to accept a standard Intel CPU cooler, be it the traditional heatsink and fan, or a water block for liquid cooling. With the current system installed [EE for Everyone] can push the individual modules up to 275 watts before the temperatures rise to unacceptable levels, though he’s hoping to push that a little higher with some future tweaks.

So what’s the end game here? Are we all expected to have a massive RGB-lit electronic load hidden under the bench? Not exactly. All of this has been part of an effort to design a highly accurate electronic load for the hobbyist which [EE for Everyone] refers to as the “Community Edition” of the project. Those smaller loads will be derived from the individual modules being used in this larger testing rig.

We’ve actually seen DIY liquid cooled electronic loads in the past, though this one certainly sets the bar quite a bit higher. For those with more meager requirements, you might consider flashing a cheap imported electronic load with an open source firmware to wring out some extra functionality.

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