Author: Al Williams

4264 Articles

That’s No Moon, Er, Selectric

August 12, 2025 by 5 Comments

If you learned to type anytime in the mid-part of the 20th century, you probably either had or wanted an IBM Selectric. These were workhorses and changed typing by moving from typebars to a replaceable element. They were expensive, though worth it since many of them still work (including mine). But few of us could afford the $1,000 or more that these machines cost back in the day, especially when you consider that $1,000 was enough to buy a nice car for most of that time. [Tech Tangents] looks at something different: a clone Selectric from the sewing machine and printer company Juki.

The typewriter was the brainchild of [Thomas O’Reilly]. He sold typewriters and knew that a $500 compatible machine would sell. He took the prototype to Juki, which was manufacturing typewriters for Olivetti at the time.

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Current Source Mixes Old School And New

August 12, 2025 by 4 Comments

At first glance, [RobBest]’s constant current source looks old school. The box is somewhat old-fashioned, featuring switches and binding posts. Most importantly, there’s a large analog meter dominating the front panel. Then you notice the OLED display, and you know something’s up.

The device can source or sink a constant current. In addition, it features a timer that calculates milliamp-hours and automatically turns off when not in use. The brain is a PIC 16F1765, which controls the screen, the buttons, and a few relays. While that might seem an odd choice for the processor, it is actually smart. The device has both a DAC and an ADC, plus an internal op amp. The analog output and a single pass transistor control the current flow, while the two relays flip it between a source and a sink.

Without that op amp, the DAC can’t produce much current. However, by passing it through the onboard amplifier, the output can drive about 100 mA, which is sufficient for this project.

This is a classic circuit, but the addition of a CPU and a display gives it capabilities that would have been very difficult to build back in the day. Want to dive into the theory behind constant current sources?  Or just the practical use of a voltage regulator to make one?

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Calipers: Do You Get What You Pay For?

August 11, 2025 by 53 Comments

Generally, you think that if you pay more for something, it must be better, right? But that’s not always true. Even if it is true at the lower end, sometimes premium brands are just barely better than the midrange. [Project Farm] looks at a bunch of different calipers — a constant fixture around the shop if you do any machining, 3D printing, or PCB layout. The price range spans from less than $10 for some Harbor Freight specials to brands like Mitutoyo, which cost well over $100. Where’s the sweet spot? See the video below to find out.

The first part of the video covers how much the units weigh, how smooth the action is, and how much force it takes to push it down. However, those are not what you probably care most about. The real questions are how accurate and repeatable they are.

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Neon Bulbs? They’re A Gas!

August 11, 2025 by 39 Comments

When you think of neon, you might think of neon signs or the tenth element, a noble gas. But there was a time when neon bulbs like the venerable NE-2 were the 555 of their day, with a seemingly endless number of clever circuits. What made this little device so versatile? And why do we see so few of them today?

Neon’s brilliant glow was noted when William Ramsay and Morris Travers discovered it in 1898. It would be 1910 before a practical lighting device using neon appeared. It was 1915 when the developer, Georges Claude, of Air Liquide fame, received a patent on the unique electrodes suitable for lighting and, thus, had a monopoly on the technology he sold through his company Claude Neon Lights.

However, Daniel Moore in 1917 developed a different kind of neon bulb while working for General Electric. These bulbs used coronal discharge to produce a red glow or, with argon, a blue glow. This was different enough to earn another patent, and neon bulbs found use primarily as indicator lamps before the advent of the LED. However, it would also find many other uses.

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Cheap Thermal Camera Fits The Bill

August 10, 2025 by 14 Comments

If you want to save a little money on a thermal camera, or if you just enjoy making your own, you should have a look at [Evan Yu’s] GitHub repository, which has a well thought out project built around the MLX90640 and an ESP32. The cost is well under $100. You can watch it do its thing in the video below.

There’s a PCB layout, a 3D-printed case, and — of course — all the firmware files.  The code uses the Arduino IDE and libraries. It leverages off-the-shelf libraries for the display and the image sensor.

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SparcStation 1+ Finally Gets Attention

August 9, 2025 by 12 Comments

We can’t throw stones. [Leaded Solder] picked up a SparcStation 1+ in 2018 and found it only produced illegal instruction errors. We’re sure he’s like us and meant to get back to it, and, instead, it sat on the bench, taking up space. You eventually have to move it, though, so seven years later, it was time for another go at it.

The first pass back in 2018 revealed that the machine had an interesting life. The full-sized hard drive was salvaged from an Apple computer. Removing the drive resolved the illegal instruction error. The drive seemed to work, but there was still nothing that suggested the machine would fully boot up. The next step was to try booting from a floppy, but that didn’t work either. The floppy cable had been surgically altered, again hinting this machine had seen some tough love.

Fast forward to 2025. This time, a Pi Pico-based SCSI emulator would stand in for the aging and suspect hard drive. Unfortunately, as noted, this machine has undergone some extensive and strange surgery. The power cable feeding the emulator had been rewired backwards, exposing the poor Pi Pico to 12 V, with predictable results. Luckily, it didn’t seem to phase the SparcStation.

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Learn C With A Lisp

August 9, 2025 by 19 Comments

One reason Forth remains popular is that it is very simple to create, but also very powerful. But there’s an even older language that can make the same claim: LISP. Sure, some people think that’s an acronym for “lots of irritating spurious parenthesis,” but if you can get past the strange syntax, the language is elegant and deceptively simple, at least at its core. Now, [Daniel Holden] challenges you to build your own Lisp as a way to learn C programming.

It shouldn’t be surprising that LISP is fairly simple. It was the second-oldest language, showing up in the late 1950s with implementations in the early 1960s. The old hardware couldn’t do much by today’s standards, so it is reasonable that LISP has to be somewhat economical.

With LISP, everything is a list, which means you can freely treat code as data and manipulate it. Lists can contain items like symbols, numbers, and other lists. This is somewhat annoying to C, which likes things to have particular types, so that’s one challenge to writing the code.

While we know a little LISP, we aren’t completely sold that building your own is a good way to learn C. But if you like LISP, it might be good motivation. We might be more inclined to suggest Jones on Forth as a good language project, but, then again, it is good to have choices. Of course, you could choose not to choose and try Forsp.