The Strange Metal Phase And Its Implications For Superconductivity

February 28, 2024 by 1 Comment

The behavior of electrons and the exact fundamentals underlying the phenomenon we call ‘electricity’ are still the subject of many competing theories and heated debates. This is most apparent in the area of superconducting research, where the Fermi liquid theory — which has has formed the foundation of much of what we thought we knew about interacting fermions and by extension electrons in a metal — was found to break down in cuprates as well as in other metals which feature a state that is a non-Fermi liquid, also called a ‘strange metal phase’.

This phase was the subject of a 2023 research article by [Liyang Chen] and colleagues in Science titled Shot Noise in a Strange Metal. As summarized in a Quanta Magazine article, the term ‘shot noise’ refers hereby to the quasiparticles that are postulated by the Fermi liquid theory to form part of the electrical current as electrons interact and ‘clump’ together, creating discrete ‘particles’ that can be measured like rain drops falling on a roof. [Liyang Chen] and colleagues created a 200 nm thin nanowire (pictured, top) out of ytterbium, rhodium and silicon, followed by cooling it down to a few Kelvin and measuring the current.

What the team found was no sign of these discrete quasiparticles, but rather non-Fermi liquid continuous current. Yet what is exactly the nature of this measured current? Quite a few attempts at explaining this phenomenon have been undertaken, e.g. Jianfan Wang et al. (2022) in rare-earth intermetallic compounds. More recently [Riccardo Arpaia] and colleagues explore charge density fluctuations (CDF) as a signature of the quantum critical point (QCP), which is a point in the phase diagram where a continuous phase transition takes place at absolute zero.

They studied the CDF using X-ray scattering in cuprate superconductors with a wide doping range, using the measured CDF as an indication of the QCP, indicating that the former may be a result of the latter. With these results mostly inspiring more discussion and research, it’ll probably be a while still before we risk replacing the Fermi liquid theory, or apply strange metal findings to produce high-temperature superconductors.

Ethernet For Hackers: Equipment Exploration

February 28, 2024 by 28 Comments

Last time, we talked about the surface-level details of Ethernet. They are fundamental to know for Ethernet hacking, but they’re also easy to pick up from bits and pieces online, or just from wiring up a few computers in your home network. Now, there’s also a bunch of equipment and standards that you will want to use with Ethernet – easy to find whether used or new, and typically as easy to work with. Let’s give you a few beacons!

Routers And Switches

Whenever you see a box with a few Ethernet ports, it’s either referred to as a router, or a switch, sometimes people will even use the word “hub”! Fortunately, it’s simpler than it may seem. A router is a smart device, typically with an OS, that ties two or more networks together – routing packers from one network to another, and typically taking care of things like handing out local IP addresses via DHCP. A switch merely helps Ethernet devices exchange packets between each other on the same level – it’s typically nowhere near as smart as a router gets. Oftentimes, a home router will contain a switch inside, so that you can plug in multiple of your home devices at once. That’s the main difference – a switch merely transmits packets between Ethernet-connected devices, while a router is a small computer taking care of packet forwarding between networks and possibly including an Ethernet switch on the side.
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The Photodiode You Never Knew You Had

February 28, 2024 by 34 Comments

Optoelectronics hold a range of possibilities for the hardware experimenter — indeed who among us hasn’t added LEDs aplenty to our work? What many of us may be unaware of though is that an LED is also a photodiode, and can even be persuaded to generate usable quantities of power. [Voltative] takes a look at this phenomenon with a series of experiments.

Lighting up an LED from a set of other LEDs is pretty cool, as is powering a calculator, or even the calculator powering itself from its on-board LED. But what caught our eye was using two LEDs as a data link, with both of them acting as transmitter and receiver (something on searching we find we’ve seen before). The possibilities there become interesting indeed.

Given that we are now surrounded by LEDs, from OLED screens to LED lighting, we can’t help wondering what the photodiode performance of some other types of part might be. Would the large area of a lighting LED give a better result for example, or would the phosphorescent coating of a white LED make it useless. We feel there’s more scope for experimentation here.

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Air Canada’s Chatbot: Why RAG Is Better Than An LLM For Facts

February 28, 2024 by 32 Comments

Recently Air Canada was in the news regarding the outcome of Moffatt v. Air Canada, in which Air Canada was forced to pay restitution to Mr. Moffatt after the latter had been disadvantaged by advice given by a chatbot on the Air Canada website regarding the latter’s bereavement fare policy. When Mr. Moffatt inquired whether he could apply for the bereavement fare after returning from the flight, the chatbot said that this was the case, even though the link which it provided to the official bereavement policy page said otherwise.

This latter aspect of the case is by far the most interesting aspect of this case, as it raises many questions about the technical details of this chatbot which Air Canada had deployed on its website. Since the basic idea behind such a chatbot is that it uses a curated source of (company) documentation and policies, the assumption made by many is that this particular chatbot instead used an LLM with more generic information in it, possibly sourced from many other public-facing policy pages.

Whatever the case may be, chatbots are increasingly used by companies, but instead of pure LLMs they use what is called RAG: retrieval augmented generation. This bypasses the language model and instead fetches factual information from a vetted source of documentation.

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A breadboard showing a tiny ESP32 board and two HMC5883L sensors connected to it on different pins

Avoid I2C Address Conflicts On ESP32 By Pin Muxing

February 28, 2024 by 20 Comments

Using hardware I2C on an ESP32? Do you need to connect multiple I2C devices with the same address? Normally, you wouldn’t be able to do that without extra parts, but on the ESP32, [BastelBaus] has found a nice hack — just connect your devices to different pins and slightly abuse the ESP32 GPIO muxing, no extra hardware required!

Initially, they tried separating SDA and SCL completely, and after a bit of tinkering, that’s worked out wonders! For this method, [BastelBaus] provides example Arduino code you could easily integrate into your project, and shows logic analyzer captures that demonstrate there’s barely any overhead. Later, they’ve also found out that you could multiplex only one of the pins, specifically, SDA, having the SCL line be common! As far as we see, this could also work out with split SCL, but do let us know if that doesn’t sound right.

Typically, such a problem is solved with an I2C multiplexer, and we’ve highlighted projects with them before. However, this simple method could also work on chips like the RP2040 or even the Raspberry Pi 4 — just a bit more limited, since the GPIO muxing for I2C has less available ports! Also, if you’re not using a chip with such a comfortable GPIO mux and you must use devices with overlapping addresses, check out the comment section under our I2C ecosystem article – there’s a fair few other methods you can use. And, if this method ever malfunctions for you, there’s a bunch of very straightforward ways you could debug your bus!

ESP32 Weather Station Looks Great With Color E-Paper Display

February 28, 2024 by 20 Comments

[educ8s.tv] has built weather stations before, but his latest is his best yet. It’s all thanks to its low-power design, enabled by its e-paper display.

The build is based around an ESP32 microcontroller, combined with a BMP180 sensor for measuring barometric pressure, and a DHT22 sensor for measuring temperature and humidity. By taking these values and feeding them into the Zambretti algorithm, it’s possible to generate a rudimentary weather forecast.

The weather station looks particularly impressive thanks to its six-color e-paper display. It’s brightly colored and easy to read, and displays graphs of temperature, pressure, and humidity over time. Plus, by virtue of the fact that it only draws power when updating, it allows the project to last a long time running solely on battery power.

As far as DIY weather stations go, this is an attractive and clean design that offers plenty of useful data to the user. We’ve seen some other neat builds in this vein before, too.

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Wire Wrap Odyssey: A 7400-series Homebrew 8-bit Computer

February 27, 2024 by 15 Comments
The Wire Wrap Odyssey's first Hello World from the CPU module, here hooked up to a logic analyzer in July of 2020. (Credit: Paul Krizak)
The Wire Wrap Odyssey’s first Hello World from the CPU module, here hooked up to a logic analyzer in July of 2020. (Credit: Paul Krizak)

As part of his computer science curriculum at Texas A&M University in the early 2000s, [Paul Krizak] took a computer architecture course on the basics of their functioning. This and being exposed to dozens of homebuilt computer projects inspired him to begin building his own 8-bit computer in 2010, which eventually grew into the Wire Wrap Odyssey. This name covers both the primary construction method chosen around 2019 in the form of wire-wrapped connections, as well the harrowing journey to reach this point with a functioning computer system despite many choices and setbacks.

The Odyssey CPU is an 8-bit microcoded design with 16-bit address bus, using mostly 74HC-series logic. A VGA graphics card is also part of the design, which can output a 640×480 text display, with character glyphs read from the system ROM (32 kB AT28C256). As for the RAM, this is an extravagant 32 kB dual-port SRAM (Renesas 7007), which also allows both the CPU and video card to use the same SRAM. Currently the system has four peripherals: a PS/2 keyboard controller, an RTC and timer (DS1511Y+), 82C52 UART and 1 MB of extended RAM, but an ATA port and parallel port are in development.

Perhaps the most impressive part about this product is the level of documentation, from the early stages including paper doodles to the current state of the system, including the GitHub repository for the software. [Paul] was also an exhibitor at the Vintage Computing Festival (VCF) SoCal recently with his Wire Wrap Odyssey, where he was able to show off the progress so far. Next year he hopes to visit VCF SoCal again, with the remaining planned peripherals implemented.