The ISS Is Getting A New WC

Every home needs renovations after a few decades, and the International Space Station is no different. This fall, they’ll be getting a new Universal Waste Management System (UWMS), aka a new toilet.

Though the news coincides with increased traffic to the ISS, this move stems from a more serious issue with bacterial contamination during longer-term space travel. Today’s ISS toilets already recycle urine back into potable water and scrub the air reclaimed from solid waste as it gets compacted and stored. The new UWMS will act more like a food dehydrator, reducing the water content as much as possible to save on space, and petrifying the poo to inactivate the bacteria.

The current commode on the American side of the ISS was designed in the 1990s and is based on the Space Shuttle’s facilities. It has a funnel with a hose for urine and a bag-lined canister with a seat for solid waste, both of which are heavily vacuum-assisted.

Though the current toilet still does everything it’s supposed to do, there is room for improvement. For instance, women find it difficult to engage both parts of the system at the same time, and almost everyone prefers the toe bars on the Russian toilet to the more encumbering thigh bars on the American throne. Also, the current commode’s interface is more complicated than it needs to be, which takes up valuable crew time. Continue reading “The ISS Is Getting A New WC”

Adding PCIe To Your Raspberry Pi 4, The Easier Way

Ever since people figured out that the Raspberry Pi 4 has a PCIe bus, the race was on to be the first to connect a regular PCIe expansion card to a Raspberry Pi 4 SBC. Now [Zak Kemble] has created a new approach, using a bridge PCB that replaces the VL805 USB 3 controller IC. This was also how the original modification by [Tomasz Mloduchowski] worked, only now it comes in a handy (OSHPark) PCB format.

After removing the VL805 QFN package and soldering in the bridge PCB, [Zak] confirmed that everything was hooked up properly and attempted to use the Raspberry Pi 4 with a PCIe extender. This showed that the Raspberry Pi would happily talk with a VL805-based USB 3.0 PCIe expansion card, as well as a Realtek RTL8111-based Ethernet card, but not a number of other PCIe cards. Exactly why this is is still unclear at this point.

As a bonus, [Zak] also found that despite the removal of the VL805 IC from the Raspberry Pi rendering its USB 3 ports useless, one can still use the USB-C ‘power input’ on the SBC as a host controller. This way one can have both PCIe x1 and USB on a Raspberry Pi 4.

This is the third iteration we’ve seen for using PCIe with the Pi. If you’re building on the work of [Thomasz Mloduchowski], which inspired [Colin Riley] to add expanders, and now this excellent hack by [Zak], we want to hear about it!

(Thanks to Itay for the tip)

Unrolling The Mystery Inside An Aluminum Electrolytic Capacitor

When we remove the enclosure of modern electronics, we see a lot of little silvery cylinders wrapped with heat shrink plastic. These aluminum electrolytic capacitors are common residents on circuit boards. We may have cut one open to satisfy our curiosity of what’s inside, but that doesn’t necessarily mean we understood everything we saw. For a more detailed guided tour, follow [TubeTime]’s informative illustrated Twitter thread.

Electronics beginners are taught the basic canonical capacitor: two metal plates and an insulator separating them. This is enough to understand the theory of capacitor operation, but there were hints the real world is not quite that simple. We don’t even need to disassemble an electrolytic capacitor to get our first hint: these cylinders have markings to indicate polarity, differentiating them from the basic capacitor which is symmetric and indifferent to polarity. Once taken apart and unrolled, we would find two thin aluminum foils separated by a sheet of paper. It would be tempting to decide the foil were our two plates and the paper is our insulator, except for the fact those two metal plates are different sizes further deviating from the basic capacitor.

Electronics veterans know the conductor–insulator–conductor pattern is not foil–paper–foil, but actually foil–oxide–electrolyte. But there is more to [TubeTime]’s tour than this answer, which includes pictures of industrial machinery, a side adventure in electrolytic chemistry using a tiny glass beaker, concluding with links to more information. And once armed with knowledge, we can better understand why electrolytic capacitors don’t necessarily need to be replaced in old equipment and appreciate them within the larger history of capacitors context.