That Handheld 386SX Gets A Teardown

June 6, 2023 by Jenny List 18 Comments

A few weeks ago our community was abuzz with the news of a couple of new portable computers available through AliExpress. Their special feature was that they are brand new 2023-produced retrocomputers, one with an 8088, and the other with a 386SX. Curious to know more? [Yeo Kheng Meng] has one of the 386 machines, and he’s taken it apart for our viewing pleasure.

What he found is a well-designed machine that does exactly what it claims, and which runs Windows 95 from a CF card. It’s slow because it’s an embedded version of the 386 variant with a 16-bit bus originally brought to market as a chip that could work with 16-bit 286-era chipsets. But the designer has done a good job of melding old and new parts to extract the most from this vintage chip, and has included some decidedly modern features unheard of in the 386 era such as a CH375B USB mass storage interface.

If we had this device we’d ditch ’95 and run DOS for speed with Windows 3.1 where needed. Back in the day with eight megabytes of RAM it would have been considered a powerhouse before users had even considered its form factor, so there’s an interesting exercise for someone to get a vintage Linux build running on it.

One way to look at it is as a novelty machine with a rather high price tag, but he makes the point that considering the hardware design work that’s gone into it, the 200+ dollar price isn’t so bad. With luck we’ll get to experience one hands-on in due course, and can make up our own minds. Our original coverage is here.

Want Lower Power? Add More Cores!

June 6, 2023 by Al Williams 35 Comments

[Jacob Beningo] over at Embedded.com recently posted his thoughts on how to do a low-power microcontroller design. On the surface, some of his advice seems a little counter-intuitive. Even he admits, “…I’m suggesting adding more cores! I must be crazy!” There are a few tips, but the part he’s talking about is that you can save power by using CPUs with multiple cores and optimizing for speed.

This seems strange since you think of additional cores and speed to consume more power. But the idea is that the faster you get your work done, the faster you can go to sleep. We’ve seen that in our own projects — faster work means more napping, and that’s good for power consumption.

Of course, it isn’t just that simple. Multiple cores don’t help you if you don’t use them. The overarching goal is to get done quickly so you can get back to sleep. You know, kind of like work. The other advice in the post is generally good, too. Measure your power consumption, respond to events, and — maybe slightly surprising — with modern CPUs, variations within the CPU family, according to [Jacob], isn’t very significant. Instead, he reports that the big changes are switching to the least-capable processor family.

Naturally, Hackaday readers are no strangers to low-power design. If you get your power consumption low enough, you can consider a low-tech battery or even a potato.

Linear Power Supply’s Current Limiter Is A Lesson In Simplicity

June 5, 2023 by Dan Maloney 5 Comments

Here at Hackaday we really like to feature projects that push the limits of what’s possible, or ones that feature some new and exciting technology that nobody has ever seen before. So what’s so exciting about this single-voltage linear power supply? Honestly, nothing — until you start looking at its thermally compensated current limiting circuit.

This one is by [DiodeGoneWild], who you’ve really got to hand it to in terms of both the empirical effort he went through to optimize the circuit, as well as the quality of his explanation. The basic circuit is dead simple: a transformer, a full-wave rectifier, an LD1085 adjustable regulator — a low-dropout version of the venerable LM317 — and associated filter caps and trimmer pot to adjust the output between 2.2 and 5.5 volts.

The current limiting circuit, though, is where things get interesting. Rather than use an op-amp, [DiodeGoneWild] chose a simple discrete transistor current-sense circuit. To make it less susceptible to thermal drift, he experimented with multiple configurations of resistors and Schottky diodes over a wide range of temperatures, from deep-freeze cold to hair-dryer-in-a-box hot. His data table and the resulting graph of current versus temperature are works of art, and they allowed him to make sensible component selections for a fixed 250-mA current limit with a reasonably flat thermal response.

As for construction, it’s all classic [DiodeGoneWild], including a PCB with traces ground out with a Dremel and a recycled heat sink. He also dropped a couple of interesting build techniques, like adding leads to turn SMD tantalum caps into through-hole components. The video below shows all the build details along with the exhaustive breadboard testing.

From taking on a potentially risky magnetron teardown to harvesting lasers from headlights, there’s always something to learn from a [DiodeGoneWild] video.

Continue reading “Linear Power Supply’s Current Limiter Is A Lesson In Simplicity” →

The Printing Of Pi

June 5, 2023 by Al Williams 15 Comments

It really isn’t necessary, but there is some geek cred to learning pi to some bizarre number of digits. One way to do that is via a piem — a mnemonic device that is easy to remember and gives you the digits. Don’t know any? [Roni Bandini] has you covered with the PiemPi machine. It prints a random piem on a thermal printer and calculates each digit on the fly. You can watch the machine in action in the video below.

Unfortunately, the Raspberry Pi Zero inside doesn’t have enough language skills to ensure the thing makes sense, so you get word salad that may or may not have any real meaning. For example, [Roni] quotes astronomer [Sir James Jeans’] phrase: “How I want a drink, alcoholic, of course, after the heavy lectures involving quantum mechanics.” Before the advent of calculators, we always used: “May I have a large container of coffee today?” In each case, you count the number of letters in each word to get the digits. However, some of the piems you can see from the machine start off with phrases like: “# leon a yahoo execution im actual total pit eagle detector christmas…”

Continue reading “The Printing Of Pi” →

Front and back views of a square, purple PCB with op amps and BNC outputs

Op Amp Contest: Generate Spirograph Shapes Using Only Op Amps And Math

June 5, 2023 by Robin Kearey 13 Comments

If you’re a child of the ’80s or ’90s, chances are you’ve spent hours tracing out intricate patterns using the pens and gears of a Spirograph kit. Simple as those parts may be, they’re actually a very clever technique for plotting mathematical functions called hypotrochoids and epitrochoids. [Craig] has spent some time analyzing these functions, and realized you can also implement them with analog circuits. He used this knowledge to design a device called Op Art which generates Spirograph shapes on your oscilloscope using just a handful of op amps.

To draw either a hypotrochoid or an epitrochoid, you need to generate sine and cosine waves of various frequencies, and then add them with a certain scaling factor. Generating sines and cosines is not so hard to do with op amps, but making an adjustable oscillator that reliably churns out matching sine and cosine waves over a large frequency range turned out to be tricky. After a bit of experimentation, [Craig] discovered that a phase-shift oscillator was the right topology, not only for its adjustability but also because it generates sine, cosine and inverted sine terms that all come in handy when drawing various Spirograph shapes. Continue reading “Op Amp Contest: Generate Spirograph Shapes Using Only Op Amps And Math” →

This Vending Machine Is For The Birds

June 5, 2023 by Al Williams 13 Comments

The early bird may get the worm, but [Stephen Chasey’s] birds only get to eat if they are smart. He’s created a vending machine for bird feeding. While this is a classic and simple exercise for a microcontroller, [Stephen’s] design is all op amps and 555 timers. The feeder comes on when it detects a warm body and waits for something to drop through a hole. Birds don’t have coins, so the hole will accept anything that will trigger the IR sensor within. In response, it dispenses a few peanuts. Rodents and squirrels won’t figure out the machinery, and so they can’t pilfer the peanuts meant for the pigeons — or other birds, even if they don’t start with the letter P.

A PIR sensor detects a warm body. A 555 keeps the system going for about 24 seconds after the last PIR event. Pairs of IR LEDs and phototransistors act as sensors that look through heat shrink tubing, which is, apparently, IR transparent. When a virtual coin drops through the hole, one of the sensors picks it up and starts another 555, which turns on a vibration motor. Another sensor watches for a nut to drop, which stops the motor. It also will time out after 11 seconds.

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Increasing System Memory With The Flick Of A Switch

June 5, 2023 by Bryan Cockfield 17 Comments

There’s an apocryphal quote floating around the internet that “640K ought to be enough memory for anybody” but it does seem unlikely that this was ever actually said by any famous computer moguls of the 1980s. What is true, however, is that in general more computer memory tends to be better than less. In fact, this was the basis for the Macintosh 512k in the 1980s, whose main feature was that it was essentially the same machine as the Macintosh 128k, but with quadruple the memory as its predecessor. If you have yet to upgrade to the 512k, though, it might be best to take a look at this memory upgrade instead.

The Fat Mac Switcher, as it is called by its creator [Kay Koba], can upgrade the memory capability of these retro Apple machines with the simple push of a switch. The switch and controller logic sit on a separate PCB that needs to be installed into the computer’s motherboard in place of some of the existing circuitry. The computer itself needs its 16 memory modules replaced with 41256 DRAM modules for this to work properly though, but once its installed it can switch seamlessly between 512k and 128k modes.

Another interesting quirk of the retro Macintosh scene is that the technically inferior 128k models tend to be valued higher than the more capable 512k versions, despite being nearly identical otherwise. There are also some other interesting discussions on one of the forum posts about this build as well. This module can also be used in reverse; by installing it in a Macintosh 512k the computer can be downgraded to the original Macintosh 128k. For this the memory modules won’t need to be upgraded but a different change to the motherboard is required.

A product like this certainly would have been a welcome addition in the mid 80s when these machines were first introduced, since the 512k was released only months after the 128k machines were, but the retrocomputing enthusiasts should still get some use out of this device and be more able to explore the differences between the two computers. If you never were able to experience one of these “original” Macintosh computers in their heyday, check out this fully-functional one-third scale replica.