Build Your Own 16 MB 30-Pin SIMMs For Vintage PCs

July 9, 2024 by Lewin Day 28 Comments

Today’s memory sticks have hundreds of pins and many gigabytes of RAM on board. Decades ago, though, the humble 30-pin SIMM was the state of the art where memory was concerned. If you’ve got vintage gear, you can try and hunt down old RAM, or you can copy [Bits und Bolts] and make your own.

Previously, [Bits und Bolts] built a 4 MB SIMM, but he’s now ramped up to building 16 MB RAM sticks — the largest size supported by the 30-pin standard. That’s a ton compared to most 30-pin sticks from the 1980s, which topped out at a feeble 1 MB.

We get to see four of his 16 MB sticks installed in a 386 motherboard, set up to operate in the appropriate Fast Page Mode. He was able to get the system operating with 64 MB of RAM, an amount still considered acceptable in the early Pentium 3 era. Hilariously, memtest took a full ten hours to complete a single pass with this configuration. [Bits and Bolts] also tried to push the motherboard further, but wasn’t able to get it to POST with over 64 MB of RAM.

As [Bits und Bolts] demonstrates, if you can read a schematic and design a PCB, it’s not that hard to design RAM sticks for many vintage computers. We’ve seen some other RAM hacks in this vein before, too.

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Putting Some Numbers On Your NEMAs

July 2, 2024 by Dan Maloney 13 Comments

It’s official: [Engineer Bo] wins the internet with a video titled “Finding NEMA 17,” wherein he builds a dynamometer to find the best stepper motor in the popular NEMA 17 frame size.

Like a lot of subjective questions, the only correct answer to which stepper is best is, “It depends,” and [Bo] certainly has that in mind while gathering the data needed to construct torque-speed curves for five samples of NEMA 17 motors using his homebrew dyno. The dyno itself is pretty cool, with a bicycle disc brake to provide drag, a load cell to measure braking force, and an optical encoder to measure the rotation of the motor under test. The selected motors represent a cross-section of what’s commonly available today, some of which appear in big-name 3D printers and other common applications.

[Bo] tested each motor with two different drivers: the TMC2209 silent driver to start with, and because he released the Magic Smoke from those, the higher current TB6600 module. The difference between the two drivers was striking, with lower torque and top speeds for the same settings on each motor using the TB6600, as well as more variability in the data. Motors did better across the board with the TBC6600 at 24 volts, showing improved torque at higher speeds, and slightly higher top speeds. He also tested the effect of microstepping on torque using the TBC6600 and found that using full steps resulted in higher torque across a greater speed range.

At the end of the day, it seems as if these tests say more about the driver than they do about any of the motors tested. Perhaps the lesson here is to match the motor to the driver in light of what the application will be. Regardless, it’s a nice piece of work, and we really appreciate the dyno design to boot — reminds us of a scaled-down version of the one [Jeremey Fielding] demonstrated a few years back.

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A Previously Unknown Supplier For A Classic Chip

June 27, 2024 by Jenny List 7 Comments

It’s common enough for integrated circuits to be available from a range of different suppliers, either as licensed clones, or as reverse-engineered proprietary silicon. In the case of a generic circuit such as a cheap op-amp it matters little whose logo adorns the plastic, but when the part in question is an application processor it assumes much more importance. In the era of the 486 and Pentium there were a host of well-known manufacturers producing those chips, so it’s a surprise decades later to find that there was another, previously unknown. That’s just what [Doc TB] has done though, finding a 486 microprocessor from Shenzhen State Micro. That’s not a brand we ever saw in our desktop computers back in the 1990s.

Analysis of a couple of these chips, a DX33 and a DX2-66, shows them to have very similar micro-architecture but surprisingly a lower power consumption suggesting a smaller fabrication process. There’s the fascinating possibility that these might have been manufactured to serve an ongoing demand for 486 processors in some as-yet-unknown Chinese industrial application, but before any retrocomputer enthusiasts get their hopes up, the chips can’t be found anywhere from Shenzhen State Micro’s successor company. So for now they’re a fascinating oddity for CPU collectors, but who knows, perhaps more information on these unusual chips will surface.

Meanwhile we’ve looked at the 486’s legacy in detail before, even finding there could still just be 486-compatible SoCs out there.

As Cheap As Chips: The MiFare Ultra Light Gets A Closer Look

June 26, 2024 by Jenny List 7 Comments

If you take public transport in many of the world’s cities, your ticket will be an NFC card which you scan to gain access to the train or bus. These cards are disposable, so whatever technology they use must be astonishingly cheap. It’s one of these which [Ken Shirriff] has turned his microscope upon, a Montreal Métro ticket, and his examination of the MiFare Ultra Light it contains is well worth a read.

The cardboard surface can be stripped away from the card to reveal a plastic layer with a foil tuned circuit antenna. The chip itself is a barely-discernible dot in one corner. For those who like folksy measurements, smaller than a grain of salt. On it is an EEPROM to store its payload data, but perhaps the most interest lies in the support circuitry. As an NFC chip this has a lot of RF circuitry, as well as a charge pump to generate the extra voltages to charge the EEPROM. In both cases the use of switched capacitors plays a part in their construction, in the RF section to vary the load on the reader in order to transmit data.

He does a calculation on the cost of each chip, these are sold by the wafer with each wafer having around 100000 chips, and comes up with a cost-per-chip of about nine cents. Truly cheap as chips!

If NFC technology interests you, we’ve taken a deep dive into their antennas in the past.

Injection Molding Using A 3D Printer

June 25, 2024 by Maya Posch 15 Comments

Recently [Stefan] of CNC Kitchen took a gander at using his gaggle of 3D printers to try injection molding (IM). Although the IM process generally requires metal molds and specialized machinery, 3D printers can be used for low-volume IM runs which is enough for limited production runs and prototyping before committing to producing expensive IM molds. In the case of [Stefan], he followed Form Labs’ guidance to produce molds from glass-infused Rigid 10K resin (heat deflection temperature of 218 °C). These molds are very rigid, as the ceramic-like noise when [Stefan] taps two together attests to.

Injection molded bolt, with imperfections on the head. (Credit: Stefan, CNC Kitchen)

The actual injection process is where things get more hairy for [Stefan], as he attempts to push the clamped-shut mold against the nozzle of the FDM printer to inject the molten plastic, rather than using an IM press. With PLA at standard extrusion temperature the plastic barely gets into the mold before solidifying, however. Following this, higher temperatures, different materials (PETG, TPU) and high flow-rate extruders are attempted, with varying results.

Many of the struggles would seem to be due to poor mold design, rather than fundamental issues with using an FDM. The Form Labs document details some of the basics, such as opening up the injection gate (to decrease pressure inside the mold), adding air vents to improve flow and so on. Commentators to the video with professional experience point out many of these issues as well, along with the benefits of preheating the mold.

With the caveat that most of the challenge is in making a good mold, we’ve even injection molding done with nothing more exotic than a hot glue gun. If you’ve got a friend, or a long enough lever, you can even inject the plastic by hand.

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Bit Of OpenSCAD Code Caps Off Wiremold

June 23, 2024 by Tom Nardi 13 Comments

Wiremold is great stuff — it’s relatively cheap, easy to work with, and offers all sorts of adapters and angle pieces which take the hassle out of running (and hiding) wires. But [Dr. Gerg] found a shortcoming of this otherwise very flexible product: since each run is intended to start and end in a surface mounted box, he couldn’t find an end cap that would let him close off a section.

The solution? A desktop 3D printer and a chunk of OpenSCAD code telling it what to extrude. When you break it down, the Wiremold profile is fairly straightforward, and can be easily described with geometric primitives. A handful of cylinders, a cube or two, tie it all together with the hull() function, and you’re there.

We’d say this would be a fantastic project to cut your OpenSCAD teeth on, but since [Dr. Gerg] was kind enough to share the source code, you don’t have to figure it out on your own. Though there’s still benefit in reading over it if you’re looking for some practical examples of how the “Programmers Solid 3D CAD Modeller” gets things done.

So why would you want a Wiremold endcap? In the case of [Dr. Gerg], it sounds like he was trying to cover up a short run of wire that was running vertically. But we could imagine other applications for this basic design now that it’s out in the wild. For example, a short length of Wiremold outfitted with a pair of printed caps could make for a nice little enclosure if you’ve got a small project that needs protecting.

Thumb Nuts For Not A Lot

June 22, 2024 by Jenny List 11 Comments

Sometimes it’s the most straightforward of hacks which are also the most satisfying, and so it is that we’d like to draw your attention to [mikeandmertle]’s PVC thumb nuts. They provide a cheap an easy to make way to create thumb-tightenable nuts for your projects.

Starting with a PVC sheet, a series of discs can be cut from it with a hole saw. The hole in the centre of the disc is chosen such that it’s a bit smaller than the required nut, so that it can be pressed into the space with a bolt and a washer. Then a second PVC disc is glued over one side of the first before being sanded to a regular shape, resulting in a captive nut at the centre of a finger-sized and easily turnable handle.

We like this project, and we think that quite a few of you will too. We wonder how much torque it will take, but we’re guessing that a threaded insert could easily be substituted for the nut in more demanding applications. And of course, for more demanding applications you could always try knurling.