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74 Articles

Sailor Hat Adds Graceful Shutdown To Pis

September 18, 2023 by 45 Comments

Even though Windows and other operating systems constantly remind us to properly eject storage devices before removing them, plenty of people won’t heed those warnings until they finally corrupt a drive and cause all kinds of data loss and other catastrophes. It’s not just USB jump drives that can get corrupted, though. Any storage medium can become unusable if certain actions are being taken when the power is suddenly removed. That includes the SD cards on Raspberry Pis, too, and if your power isn’t reliable you might consider this hat to ensure they shut down properly during power losses.

The Raspberry Pi hat is centered around a series of supercapacitors which provide power for the Pi temporarily. The hat also communicates with the Pi to let it know there is a loss of power, so that the Pi can automatically shut itself down in that situation to prevent corrupting the memory card. The hat is more than just a set of backup capacitors, though. The device is capable of taking input power from a wide range of sources and filtering it for the power requirements of the Pi, especially in applications like boats and passenger vehicles where the input power might be somewhat noisy. There’s an optocoupled CAN bus interface as well for those looking to use this for automotive applications.

The entire project is also available on the project’s GitHub page for those wishing to build their own. Some sort of power backup is a good idea for any computer, though, not just Raspberry Pis. We’ve seen uninterruptible power supplies (UPS) with enough power to run an entire house including its computers, to smaller ones that’ll just keep your Internet online during a power outage.

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Clean Water, From A Plant-Based Filter

September 9, 2023 by 20 Comments

If you’re an outdoors person, one of the earliest things you learned was probably that in-field water sources can’t always be trusted as drinkable. A clear mountain stream could have a dead sheep in it just upstream, for example. Maybe you learned to boil it, or perhaps add chemical tablets. Up-to-date campers have a range of filters at their disposal thanks to nanotechnology, but such devices aren’t the only options to avoid sickness. [BeraAjan] has built one using plant xylem.

The inspiration for this filter came from an MIT paper, and the plant xylem in question isn’t the thin layer we were expecting but a far thicker one found in young conifer branches. In fact, the whole twig without its bark is placed in a tube, and the water filters through it.

It’s fair to say that this isn’t the fastest of filters though, as you can see in the video below the break. He’s combined a few individual filters, but maybe it’s not for the easily bored.

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Clean Up Your Resin-Printing Rinse With Dialysis

September 5, 2023 by 64 Comments

There’s a lot to like about resin 3D printing. The detail, the smooth surface finish, the mechanical simplicity of the printer itself compared to an FDM printer. But there are downsides, too, not least of which is the toxic waste that resin printing generates. What’s one to do with all that resin-tainted alcohol left over from curing prints?

How about sending it through this homebrew filtering apparatus to make it ready for reuse? [Involute] likens this process to dialysis, and while we see the similarities, what’s going on here is a lot simpler than the process used to filter wastes from the blood in patients with failing kidneys — there are no semipermeable membranes used here. Not that the idea suffers from its simplicity, mind you; it just removes unpolymerized resin from the isopropyl alcohol rinse using the same photopolymerization process used during printing. Continue reading “Clean Up Your Resin-Printing Rinse With Dialysis” →

Low-Frequency DC Block Lets You Measure Ripple Better

May 10, 2023 by 12 Comments

We all know how to block the DC offset of an AC signal — that just requires putting a capacitor in series, right? But what if the AC signal doesn’t alternate very often? In that case, things get a little more complicated.

Or at least that’s what [Limpkin] discovered, which led him to design this low-frequency DC block. Having found that commercially available DC blocks typically have a cutoff frequency of 100 kHz, which is far too high to measure power rail ripple in his low-noise amplifier, he hit the books in search of an appropriate design. What he came up with is a  non-polarized capacitor in series followed by a pair of PIN diodes shunted to ground. The diodes are in opposite polarities and serve to limit how much voltage passes out of the filter. The filter was designed for a cutoff frequency of 6.37 Hz, and [Limpkin]’s testing showed a 3-dB cutoff of 6.31 Hz — not bad. After some torture testing to make sure it wouldn’t blow up, he used it to measure the ripple on a bench power supply.

It’s a neat little circuit that ended up being a good learning experience, both for [Limpkin] and for us.

A Loving Look Inside Vacuum Fluorescent Displays

February 26, 2023 by 20 Comments

Everyone knows we’re big fans of displays that differ from the plain old flat-panel LCDs that seem to adorn most devices these days. It’s a bit boring when the front panel of your widget is the same thing you stare at hour after hour while using your phone. Give us the chunky, blocky goodness of a vacuum fluorescent display (VFD) any day of the week for visual interest and retro appeal.

From the video below, it seems like [Posy] certainly is in the VFD fandom too, rolling out as he does example after example of unique and complicated displays, mostly from audio equipment that had its heyday in the 1990s. In some ways, the video is just a love letter to the VFD, and that’s just fine with us. But the teardowns do provide some insights into how VFDs work, as well as suggest ways to tweak the overall look of a VFD.

For example, consider the classy white VFDs that graced a lot of home audio gear back in the day. It turns out, the phosphors used in those displays weren’t white, but closer to the blue-green color that VFDs are often associated with. But put a pink filter between the display and the world, and suddenly those turquoise phosphors look white. [Posy] does a lot of fiddling with the stock filters to change the look of his VFDs, some to good effect, others less so.

As for the internals of VFDs, [Posy]’s look at a damaged display reveals a lot about how they work. With a loose scrap of conductor shorting one of the cathodes inside the tube, the damaged VFD isn’t much to look at, and is beyond reasonable repair, but it’s kind of cool to examine the spring mechanisms that take up slack as the cathodes heat up and expand.

Thanks to [Posy] for this heartfelt look into the VFDs of yesterday. If you need more about how VFDs work, we’ve covered that before, too.

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How To Restore A Musical Amiga

December 24, 2022 by 21 Comments

Despite the huge strides in computing power and functionality that have been achieved in the past few decades, there are still some things that older computers can do which are basically impossible on modern machines. This doesn’t just include the ability to use older hardware that’s now obsolete, either, although that is certainly a perk. In this two-part restoration of an Amiga 500, [Jeremy] shows us some of these features like the ability to directly modify the audio capabilities of this retro machine.

The restoration starts by fixing some damage and cleaning up the rest of the machine so it could be powered up for the first time in 30 years. Since it was in fairly good shape he then started on the fun part, which was working with this computer’s audio capabilities. It includes a number of amplifiers and filters in hardware that can be switched on or off, so he rebuilt these with new op-amps and added some new controls so that while he is using his MIDI software he can easily change how it sounds. He also restored the floppy disk drives and cleaned up the yellowing on the plastic parts to improve the overall appearance, as well as some other general improvements.

These old Amigas have a lot going for them, but since [Jeremy] is a musician he mostly focused on bringing back some of the musical functionality of his childhood computer, although he did build up a lot of extra features in this machine as well. These types of audio circuits are not something found in modern computers, though, so to get a similar sound without using original hardware you’ll need to build something like this NES audio processing unit programmed in Verilog.

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Pie Stop For Emergency DNS Needs

November 24, 2022 by 37 Comments

The war on Internet ads rages on, as the arms race between ad blockers and ad creators continues to escalate. To make a modern Internet experience even remotely palatable, plenty of people are turning to DNS-level filters to stop the ads from coming into the network at all. This solution isn’t without its collateral damage though, as the black lists available sometimes filter out something that should have made it to the user. For those emergencies, [Kristopher] created the Pie Stop, a physical button to enact a temporary passthrough on his Pi-Hole.

While [Kristopher] is capable of recognizing a problem and creating the appropriate white list for any of these incidents, others in his household do not find this task as straighforward. When he isn’t around to fix the problems, this emergency stop can be pressed by anyone to temporarily halt the DNS filtering and allow all traffic to pass through the network. It’s based on the ESP-01S, a smaller ESP8266 board with only two GPIO pins. When pressed, it sends a custom command to the Pi-Hole to disable the ad blocking. A battery inside the case allows it to be placed conveniently anywhere near anyone who might need it.

With this button deployed, network snafus can be effectively prevented even with the most aggressive of DNS-level ad blocking. If you haven’t thought about deploying one of these on your own network, they’re hard to live without once you see how powerful they are. Take a look at this one which also catches spam.