Inside A Mystery 1980s Filter IC Featuring Switched Capacitors

October 11, 2026 by 2 Comments

Recently [Ken Shirriff] got handed a mystery IC by [CuriousMarc] who had found said IC in a box of various old chips. Labelled only with a date code of the 47th week of 1985 and a mysterious F1-10-5 alongside a logo that didn’t lead to any hits in the typical IC databases, it was up to [Ken] to figure out what lurks inside this CDIP chip.

As it turns out, it’s actually a pretty interesting IC with an easy to identify die once the ceramic package had been cracked open with a surgical hammer-and-chisel strike.

With the die under a microscope it was identified as a Harris HF10, itself a variant of the National Semiconductor MF10. This is a dual switched capacitor filter, with the modern version being e.g. the TI MF10-N in both PDIP and SOIC, but sadly no CDIP any more. Availability seems scarce, so the MF10 may not be long for this world.

These filter ICs can tune their capacitors to act as a low-, band- or high-pass filter. How this works is explained by [Ken], with switched capacitors replacing the resistors of a typical filter circuit. The main reasons for doing this over just using a resistor include how large resistors can get compared to the relatively small capacitor, not to mention their fixed value versus the adjustable resistance from the switchable capacitor.

The remainder of the circuit is mostly there to enable the switching and overall operation, providing a fascinating glimpse at a chip that would have been incredibly useful in the 1980s, including in synthesizers where this adjustable filter feature was most convenient.

A PCB layout is superimposed on a grey grid of hexagonal cells. The PCB traces mostly bend at 120-degree angles, and an integrated circuit's footprint is tilted at an angle matching the grid.

Improving An Autorouter With A Hexagonal Grid

October 11, 2026 by 4 Comments

Despite the recent leaps forward in other forms of computer-driven design, the reliability of PCB autorouters remains questionable; on the positive side, though, the lack of massive training data makes them plausible for a determined programmer to implement. For anyone contemplating this undertaking, [James Bowman] recommends a slightly unusual choice: use a hexagonal layout grid.

[James] built his own autorouter in his CuFlow PCB layout program. It takes a fairly straightforward approach: it represents the board as a grid of cells, and uses Lee’s algorithm to find the shortest routes between connected cells. The program initially used a square grid, but a hexagonal grid had a few advantages: in particular, each cell has six equidistant neighbors, rather than four (or eight, if you accept diagonal neighbors at a different distance), which allows denser routing. Because a hexagon more closely approximates a circle than a square, the same minimum-distance rules allow smaller cells, allowing the autorouter to pack more traces into the same space.

While we have previously seen a self-built autorouter, it’s much more common to interface with an external tool. If you start to get into high-speed PCB routing, though, building an autorouter becomes much harder.

Mars Pathfinder: What Really Happened?

October 11, 2026 by 8 Comments

You’ve probably heard of Mars Pathfinder, the NASA lander and its Sojourner rover that took up residence on Mars in 1997. At first, all was well, but after a few days, the lander suffered a series of total system resets. A watchdog timer detected a problem and forced reboots. [Vivek Bhageria’s] recent post looks into what happened and the eventual solution.

The root cause was priority inversion. This happens when a lower-priority task holds a resource needed by a higher-priority task and prevents the higher-priority task from executing. In this case, the operating system was VxWorks, but this can happen on any kind of priority scheduling system.

The simplified version is that there were two tasks that each used the same mutex to avoid stepping on each other. The highest priority was a data distribution task. The lowest priority task dealt with meteorology data processing. There was also a medium-priority task that handled bus maintenance.

The failure would occur when the low-priority task had the mutex and lost its time slot before releasing it. The high-priority task would then find it couldn’t take the mutex. However, the low-priority task didn’t get control again because of the medium-priority tasks waiting to run.

In effect, the high-priority task was now waiting on something that couldn’t become available until the lowest-priority task was able to run. That’s priority inversion.

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Slim Type For Small Screens, With PixelFonts

October 10, 2026 by 7 Comments

Small displays are affordable and easy to use, but their size can present a challenge. To help address this, [mcer12] created PixelFonts, a family of condensed fonts designed specifically for low-resolution displays, making sure every line holds as much text as it can fit.

PixelFonts works alongside either the AdafruitGFX or U8g2 libraries; one writes to the display using the common syntax of the chosen library, and the font itself comes from PixelFonts. Text can be displayed in regular and 3D shadowed versions, as well as in a wide variety of heights and weights. There’s support for accented letters, albeit only in lowercase due to space constraints. Want to make some changes? Every font comes with a BDF file to make alterations as widely accessible as possible.

Making the most of every pixel is important with small displays, but there’s more than one way to do so. For example, when it comes to color LCDs, subpixel rendering can improve legibility of small fonts; another way to get the most out of limited display sizes.

Unique Archeological Discovery Sheds Light On Neanderthal Wooden Tool Usage

October 10, 2026 by 2 Comments

The Abric Romaní site in Spain is rather unique in archeology for one simple reason: the caves in its limestone-rich cliff have seen humanoid occupation for thousands of years. A thick layer of calcium carbonate-based travertine deposit has, over time, covered and largely preserved tools and other implements, including those made of wood. Over many decades of archeological exploration, 597 wooden imprints have been uncovered, with a recent research article by [Palmira Saladié] et al. detailing these findings.

Wood is one of those archaeological artefacts that are very elusive due to their fragility, even though we know that wood has been used pretty much everywhere from the first day that a humanoid critter discovered that branches make great clubs and spears, and can also easily be shaped to make them even more useful.

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Poking At The Radxa Dragon Q8B Raspberry Pi 5 Killer

October 10, 2026 by 14 Comments

Although the asking price of $209 plus shipping seems high for the Radxa Dragon Q8B, featuring the Qualcomm SC8280XP and 8 GB of LPDDR4X, this is 2026, and amid the RAMpocalypse, even the 8 GB LPDDR4X-equipped Raspberry Pi 5 now costs $175. This, to [Jeff Geerling], makes it fair to directly compare the two to see whether you may want to consider this board for more intense computing purposes.

There’s also a written summary of the results and details in a GitHub issue, though the direct comparison with the Raspberry Pi 5 is in the video.

Although this Qualcomm SoC isn’t new, its primary use is for Windows laptops, which gives somewhat of a hint as to what its performance may be like, tempered by the fact that it was announced in 2021.

The Dragon QXB offers about 2x everything over the RPi5, plus Windows and UEFI support. For Linux, it appears that you still need customized images, which seems perplexing in light of the UEFI aspect. You also have to pick between different Linux images from Radxa and use their Rsetup update tool, making it a less than newbie-friendly offering.

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Valve Releases Hardware And CAD Reference For New VR Headset

October 10, 2026 by 7 Comments

Valve recently began shipping its long-awaited VR headset, the Steam Frame. Now, there is a hardware reference repository that includes everything a budding modder might need, and then some.

No need to 3D scan or break out the calipers if one wants to design their own add-ons.

Want to design and 3D print some add-ons, or a carrying case, or some other doodad? There’s no need to break out the calipers or 3D scan the hardware. The repository contains STEP format models of the VR core module, head strap, and controllers, so it’s as easy as possible to design things that’ll fit. The location of the IR tracking LEDs embedded in the controllers is also documented, so one can ensure their design doesn’t occlude them.

That’s not all. The Frame has a user-accessible hardware expansion port at its front. This port exposes two interfaces: high-speed MIPI camera and PCI Express. This expansion port is documented in the repository, and even has a simple reference design built in both KiCad and Altium.

We’re glad to see Valve maintain their hacker-friendly hardware design with the Steam Frame. Demand for The Frame outstrips supply so far, so if you’re on the waitlist, you might want to browse the repository and get an early start on whatever customizations you have in mind while you wait for your confirmation. And when you get something working, drop us a note on the tips line!