The Benefits Of Displacement Ventilation

The world has been shaken to its core by a respiratory virus pandemic. Humanity has been raiding the toolbox for every possible weapon in the fight, whether that be masks, vaccinations, or advanced antiviral treatments.

As far as medicine has come in tackling COVID-19 in the past two years, the ultimate solution would be to cut the number of people exposed to the pathogen in the first place. Improving our ventilation methods may just be a great way to cut down on the spread. After all, it’s what they did in the wake of the Spanish Flu.

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Tricking A Smart Meter Into Working On The Bench

When the widget you’re working on is powered by a battery or a USB charger, running it on the bench is probably pretty safe. But when the object of your reverse-engineering desire is a residential electrical meter, things can get a little dicey.

Not that this elevated danger level has kept [Hash] from exploring the mysteries presented by smart meters. Still, with a desire to make things a little safer, he came up with a neat trick for safely powering electrical meters on the bench. [Hash] found that the internal switch-mode power supply on the meter backplane was easy enough to back-feed with a 12-volt bench supply, rather than supplying the meter with the full 240-volt AC supply it normally gets when plugged into a meter base (these are meters for the North American market, where split-phase 240-volt is the norm for residential connections.) But that wasn’t enough for the meter — it powered up, but stayed in a reset state without fully booting. Something more was needed to bring the meter fully to life.

That something proved to be a small AC signal. Normally, a resistor network divides the 240-volt supply down to about 3 volts, which is used by the sensing circuit in the meter. [Hash] found that injecting a 60-Hz, 600-mV sine wave signal with about a 3-volt DC bias into the sensing circuit was enough to spoof the meter into thinking it’s plugged into the meter base. The video below has a walkthrough of the hack, and some nice shots of the insides of the meters he’s been working with.

[Hash] has been working with these meters for a while now, and some of the stuff he’s learned is pure gold. Be sure to check out his 2021 Remoticon talk on meter hacking for all the fascinating details.

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Building A Mechanical Oscillator, Tesla Style

Before Tesla devised beautifully simple rotary machinery, he explored other methods of generating alternating current. One of those was the mechanical oscillator, and [Integza] had a go at replicating the device himself. (Video, embedded below the break.)

Initial attempts to reproduce the technology using 3D-printed parts were a failure. The round cylinder had issues sealing, and using O-ring seals introduced too much friction to allow the device to oscillate properly. A redesign that used external valving and a square cylinder proved more successful.

Once the oscillator was complete, the output shaft was fitted with magnets and a coil to generate electricity. After generating a disappointing 0.14 volts, [Integza] went back and had a look at the Maxwell-Faraday equations. Using this to guide the design, a new coil was produced with more turns, and the magnetic flux was maximised. With this done, the setup could generate seven volts, enough to light several LEDs.

While it’s not a particularly efficient generator, it’s a great proof-of-concept. Yes, Tesla’s invention worked, but it’s easy to see why he moved on to rotary designs when it came to real-world applications. We’ve seen [Integza] take on other builds too, like the ever-popular Tesla turbine.

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Hackaday Links: July 28, 2019

It looks like Apple is interested in buying Intel’s modem chip business. Seriously interested; a deal worth $1 billion could be announced as early as this week. That might look like a small potato purchase to the world’s biggest company – at least by market capitalization – but since the technology it will be buying includes smartphone modems, it provides a look into Apple’s thinking about the near future with regard to 5G.

It turns out that Make Magazine isn’t quite dead yet. [Dale Dougherty], former CEO of Maker Media, which went under in June, has just announced that he and others have acquired the company’s assets and reformed under the name “Maker Community LLC.” Make: Magazine is set to resume publication, going back to its roots as a quarterly publication in the smaller journal format; sadly there’s no specific word about the fate of Maker Faire yet.

The hoopla over the 50th anniversary of Apollo 11 may be over, but we’d be remiss not to call out one truly epic hack related to the celebration: the full restoration of an actual Apollo Guidance Computer. The AGC was from a test model of the Lunar Module, and it ended up in the hands of a private collector. Since November of 2018 the AGC has been undergoing restoration and tests by [Ken Shirriff], [Mike Stewart], and [Carl Claunch]. The whole effort is documented in a playlist by [Marc “CuriousMarc” Verdiell] that’s worth watching to see what was needed to restore the AGC to working condition.

With the summer sun beating down on the northern hemisphere, and air conditioners at working extra hard to keep things comfortable. [How To Lou] has a quick tip to improve AC efficiency. Turns out that just spraying a fine mist of water on the condenser coils works wonders; [Lou] measured a 12% improvement in cooling. It may not be the best use of water, and it may not work as well in very humid climates, but it’s a good tip to keep in mind.

Be careful with this one; between the bent spoon, the syringe full of amber liquid, and the little candle to heat things up, this field-expedient reflow soldering setup might just get you in trouble with the local narcotics enforcement authorities. Even so, knowing that you can assemble a small SMD board without a reflow oven might prove useful someday, under admittedly bizarre circumstances.

From the “Considerably more than 8-bits music” file, check out the Hull Philharmonic Orchestra’s “8-Bit Symphony.” If your personal PC gaming history included a Commodore 64, chances are you’ll recognize songs from titles like “Monty on the Run”, “Firelord”, “Green Beret”, and “Forbidden Forest.” Sure, composers like [Ben Daglish] and [Paul Norman] worked wonders with the three-channel SID chip, but hearing those tunes rendered by a full orchestra is something else entirely. We found it to be particularly good background music to write by.

Scott Swaaley On High Voltage

If you were to invent a time machine and transport a typical hardware hacker of the 1970s into 2018 and sit them at a bench alongside their modern counterpart, you’d expect them to be faced with a pile of new things, novel experiences, and exciting possibilities. The Internet for all, desktop computing fulfilling its potential, cheap single-board computers, even ubiquitous surface-mount components.

What you might not expect though is that the 2018 hacker might discover a whole field of equivalent unfamiliarity while being very relevant from their grizzled guest. It’s something Scott Swaaley touches upon in his Superconference talk:  “Lessons Learned in Designing High Power Line Voltage Circuits” in which he describes his quest for an electronic motor brake, and how his experiences had left him with a gap in his knowledge when it came to working with AC mains voltage.

When Did You Last Handle AC Line voltages?

If you think about it, the AC supply has become something we rarely encounter for several reasons. Our 1970s hacker would have been used to wiring in mains transformers, to repairing tube-driven equipment or CRT televisions with live chassis’,  and to working with lighting that was almost exclusively provided by mains-driven incandescent bulbs. A common project of the day would have been a lighting dimmer with a triac, by contrast we work in a world of microcontroller-PWM-driven LEDs and off-the-shelf switch-mode power supplies in which we have no need to see the high voltages. It may be no bad thing that we are rarely exposed to high-voltage risk, but along the way we may have lost a part of our collective skillset.

Scott’s path to gaining his mains voltage experience started in a school workshop, with a bandsaw. Inertia in the saw kept the blade moving after the power had been withdrawn, and while that might be something many of us are used to it was inappropriate in that setting as kids are better remaining attached to their fingers. He looked at brakes and electrical loads as the solution to stopping the motor, but finally settled on something far simpler. An induction motor can be stopped very quickly indeed by applying a DC voltage to it, and his quest to achieve this led along the path of working with the AC supply. Eventually he had a working prototype, which he further developed to become the MakeSafe power tool brake.

Get Your AC Switching Right First Time

The full talk is embedded below the break, and gives a very good introduction to the topic of switching AC power. If you’ve never encountered a thryristor, a triac, or even a diac, these once-ubiquitous components make an entrance. We learn about relays and contactors, and how back EMF can destroy them, and about the different strategies to protect them. Our 1970s hacker would recognise some of these, but even here there are components that have reached the market since their time that they would probably give anything to have. We see the genesis of the MakeSafe brake as a panel with a bunch of relays and an electronic fan controller with a rectifier to produce the DC, and we hear about adequate safety precautions. This is music to our ears, as it’s a subject we’ve touched on before both in terms of handling mains on your bench and inside live equipment.

So if you’ve never dealt with AC line voltages, give this talk a look. The days of wiring up transformers to power projects might be largely behind us, but the skills and principles contained within it are still valid.

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Down The DIY Rabbit Hole With A Shop AC Installation

There’s a fine line between a successful DIY project and one that ends in heartbreak. It’s subjective too; aside from projects that end up with fire trucks or ambulances in the driveway, what one DIYer would consider a disaster might be considered a great learning opportunity to someone else.

We’re pretty sure [Cressel] looks at his recent DIY mini-split AC installation for his shop as a series of teachable moments. Most folks leave HVAC work to the pros, but when you run a popular YouTube channel where you make your own lathe from scratch, you might be persuaded to give anything a go. [Cressel] did everything possible to do this job like a pro, going so far as to get training in the safe handling of refrigerants and an EPA certification so he knew how to charge the system correctly. He also sunk quite a bit of money into tools; between the manifold gauge set, vacuum pump, and various plumbing bits, that was a hefty $300 bite alone.

The install went well until he started charging the refrigerant, when a mistake with a fitting caused him to contaminate his nice, new batch of R-410A. Rather than back out and call a pro to finish up, [Cressel] stuck with it, to the tune of $900 in extra tools and materials needed to recover the old refrigerant safely and replace it with virgin R-410A. The video below has a condensed version of the whole tale.

It all worked out in the end, but at a cost that probably meets or exceeds what an HVAC contractor would have charged. [Cressel] seems like a glass-half-full kind of guy, though, so we expect he’s happy to have learned something new, and to have a bunch of neat new tools to boot.

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A Dramatic Demo Of AC Versus DC Switching

Switches seem to be the simplest of electrical components – just two pieces of metal that can be positioned to either touch each other or not. As such it would seem that it shouldn’t matter whether a switch is used for AC or DC. While that’s an easy and understandable assumption, it can also be a dangerous one, as this demo of AC and DC switching dramatically reveals.

Using a very simple test setup, consisting of an electric heater for a load, a variac to control the voltage, and a homemade switch, [John Ward] walks us through the details of what happens when those contacts get together. With low-voltage AC, the switch contacts exhibit very little arcing, and even with the voltage cranked up all the way, little more than a brief spark can be seen on either make or break. Then [John] built a simple DC supply with a big rectifier and a couple of capacitors to smooth things out and went through the same tests. Even at a low DC voltage, the arc across the switch contacts was dramatic, particularly upon break. With the voltage cranked up to the full 240-volts of the UK mains, [John]’s switch was essentially a miniature arc welder, with predictable results as the plastic holding the contacts melted. Don your welding helmet and check out the video below.

As dramatic as the demo is, it doesn’t mean we won’t ever be seeing DC in the home. It just means that a little extra engineering is needed to make sure that all the components are up to snuff.

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