The Stern-Gerlach Experiment Misunderstood

Two guys — Stern and Gerlach — did an experiment in 1922. They wanted to measure magnetism caused by electron orbits. At the time, they didn’t know about particles having angular momentum due to spin. So — as explained by [The Science Asylum] in the video below — they clearly showed quantum spin, they just didn’t know it and Physics didn’t catch on for many years.

The experiment was fairly simple. They heated a piece of silver foil to cause atoms to stream out through a tiny pinhole. The choice of silver was because it was a simple material that had a single electron in its outer shell. An external magnet then pulls silver atoms into a different position before it hits some film and that position depends on its magnetic field.

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The Disappearing Capacitor

As part of a phosphorescence detector, [lcamtuf] has been working with photodiodes. The components, like all diodes, have some capacitance at the junction, and this can limit performance. That’s why [lcamtuf] turned to bootstrapping to make that parasitic capacitance almost disappear.

The technique appears in several Analog Devices datasheets that presents a mystery. An op amp circuit that would normally limit changes to about 52 kHz has an unusually-placed JFET and claims to boost the bandwidth to 350 kHz.

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The 6GHz Band Opens In The US

On December 11th, the FCC announced that the band around 6GHz would be open to “very low-power devices.” The new allocation shares space with other devices already using these frequencies. The release mentions a few limitations over the 350 MHz band (broken into two segments). First, the devices must use a contention-based protocol and implement transmit power control. The low-power devices may not be part of a fixed outdoor infrastructure.

The frequencies are 6.425-6.525 GHz, 6.875-7.125 GHz and the requirements are similar to those imposed on 802.11ax in the nearby U-NII-5 and U-NII-7 bands.

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Pico Logic Analyzer Gets New Version

[Happy Little Diodes] built a Pi Pico logic analyzer designed by [El Dr. Gusman] using the original design. But he recently had a chance to test the newest version of the design, which is a big upgrade. You can see his take on the new design in the video below.

The original design could sample 24 channels at 100 MHz and required two different PCBs. The new version uses a single board and can operate up to 400 MHz. There’s also a provision for chaining multiple boards together to get more channels. You can set the level shifters to use 5 V, 3.3 V, or an external voltage. Since [Happy] is working on a ZX Spectrum, the 5 V conversion is a necessity.

The code is on GitHub, although it warns you that version six — the one seen in the video — isn’t stable, so you might have to wait to make one on your own. The software looks impressive and there may be some effort to integrate with Sigrok.

If you missed our coverage of the earlier version, you can still catch up. Dead set on Sigrok support? [Pico-Coder] can help you out.

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It’s Remotely Ham Radio

Have you ever considered running your ham radio remotely? It has been feasible for years but not always easy. Recently, I realized that most of the pieces you need to get on the air remotely are commonplace, so I decided to take the plunge. I won’t give step-by-step instructions because your radio, computer setup, and goals are probably different from mine. But I will give you a general outline of what you can do.

I’m fortunate enough to have a sizeable freestanding shop in my backyard. When I had it built, I thought it was huge. Now, not so much. The little space is crammed with test equipment, soldering gear, laser cutters, drill presses, and 3D printers. I’ve been a ham for decades, but I didn’t have room for the radios, nor did I have an antenna up. But a few months ago, I made space, set some radios up, strung out a piece of wire, and got back on the air. I had so much fun I decided it was time to buy a new radio. But I didn’t want to have to go out to the shop (or the lab, as I like to call it) just to relax with some radio time.

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Cheap FPGA PCIe Development

Typically, if you want to build an FPGA project inside a PC, you’d need a fairly expensive development board that plugs into the bus. However, [CircuitValley] found some IBM RS-485 boards that are little more than a PCIe board with an Intel FPGA onboard. These are widely avaiable on the surplus market for around $20 shipped. He’s been documenting how to use them.

The FPGA onboard is a Cyclone IV with about 21,000 logic elements and a little over 750 kbits of memory. The board itself has configuration memory, power management, and a few connectors. The JTAG header is unpopulated, but the footprint is there. You simply need to supply a surface-mount pin header and an external JTAG probe, and you can program. Even if you aren’t interested in using an FPGA board, the reverse engineer steps are fun to watch.

The situation reminds us a little of the RTL-SDR — when a device uses a programmable device to perform nearly all of its functions, it is subject to your reprogramming. What would you do with a custom PCIe card? You tell us. Need a refresher on the bus? We can help. Thinking of building some sort of FPGA accelerator? Maybe try RIFFA.

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Microchess Remembered

Playing chess has always been a bellwether for computers. The game isn’t trivial, but the rules are managably simple. However, the game is too complex to be easily solved entirely, so you have to use tricky software to play a credible game. Big computers do have an advantage, of course. But Microchess — arguably the first commercial game for home computers — was able to play on tiny machines like the Kim-1. [Joachim Froholt] interviewed [Peter Jennings] — the man behind Microchess to learn the whole story of its creation.

In 1960, [Jennings] was ten years old and had to persuade the local librarian to let him read adult books on electronics and computers. Five years later, a ham radio teletype and some circuitry helped him practice chess openings and was the first of many chess-playing machines he’d build or program.

Microchess itself took six months of painstaking programming, entering hex codes into the computer. Word leaked out from a user’s group meeting (where Microchess beat a human player), and [Jennings] was swamped with requests for the program. In late 1976, the program was offered for sale as a teletype listing or, for an extra $3, a cassette tape.

The program went on to be very successful and moved to other platforms. Commodore even made a special dedicated device based on the Kim-1 to play Microchess, a piece of hardware unique enough that [Michael Gardi] honored it with one of his phenomenal replicas.