Commodore Datasette Does Its Own Calibration

Ah, the beloved Commodore 64. The “best-selling computer system of all time”. And hobbyists are keeping the dream alive, still producing software for it today. Which leads us to a problem with using such old equipment. When you get your copy of Petscii Robots on cassette, and try to fastload it, your machine might just consistently fail to load the program. That’s fine, time to pull out the cue-tips and rubbing alcohol, and give the read heads a good cleaning. But what if that doesn’t do the job? You may just have another problem, like tape speed drift.

There are several different ways to measure the current tape speed, to dial it in properly. The best is probably a reference cassette with a known tone. Just connect your frequency counter or digital oscilloscope, and dial in the adjustment pot until your Datasette is producing the expected tone. Oh, you don’t have a frequency counter? Well good news, [Jan Derogee] has a solution for you. See, you already have your Datasette connected to a perfectly serviceable frequency counter — your Commodore computer. He’s put out a free program that counts the pulses coming from the Datasette in a second. So play a reference cassette, run the program, and dial in your Datasette deck. Simple! Stick around after the break for a very tongue-in-cheek demonstration of the problem and solution.

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3D Printable Bearings That Actually Work, No CAD Tweaking Required

3D printing bearings with an FDM printer can be an iffy endeavor, but it doesn’t have to be that way. [Matvey Kukuy]’s Ultimate 608 Bearing with Calibration Kit is everything you’ll need to dial in and print functional 608-style print-in-place bearings on your 3D printer.

Calibration pieces have a handy label attached for identification.

[Matvey] found that there are two key tolerances to get right. And by “get right” he means “empirically determine which works best with your filament and printer”. But don’t worry, there’s no need to get into CAD work to make that happen. [Matvey] has exported a staggering 64 slightly different calibration models (and their matching production versions) along with a printable testing tool. With the help of a step-by-step process that resembles a sort of binary search, one can take the Goldilocks approach to find just the right model for one’s filament and printer in a minimum of steps.

There’s one more tip as well: [Matvey] says that once you determine the best model to use, don’t fill the print bed with copies, unless you want a bed full of possibly non-working bearings! Why is this? A 3D printer prints a bed full of objects slightly differently than it prints a single one, and since the margin for error on the perfectly-selected bearing is so small, that can be enough to keep it from working. To print more than one bearing at a time, position them far from each other and use something like PrusaSlicer’s sequential printing, which is an option to print each object completely before starting the next one.

[Matvey]’s own best results came from printing with PLA at a layer height of 0.16 mm. He also used grease in the bearing to improve performance and extend its life. He doesn’t specify what kind of grease he used, but we’d recommend a plastic-safe grease like PTFE-based Super Lube.

Have you used 3D printed bearings in a project? Would [Matvey]’s design be helpful to you? Let us know all about it in the comments.

Programmable Resistance Box

For prototype electronics projects, most of us have a pile of resistors of various values stored somewhere on our tool bench. There are different methods of organizing them for easy access and identification, but for true efficiency a resistance substitution box can be used on the breadboard to quickly change resistance values at a single point in a circuit. Until now it seemed this would be the pinnacle of quickly selecting differently-sized resistors, but thanks to this programmable resistor bank there’s an even better option available now.

Unlike a traditional substitution box or decade box, which uses switches or dials to select different valued resistors across a set of terminals, this one is programmable and uses a series of sealed relays instead. That’s not where the features stop, though. It also comes equipped with internal calibration circuitry which take into account the resistance of the relay contacts and internal wiring to provide a very precise resistance value across its terminals. It’s also able to be calibrated manually to account for temperature or other factors.

For an often-overlooked piece of test equipment, this one surely fits the bill of something we didn’t know we needed until now. Even though digital resistor substitution boxes are things we have featured in the past, the connectivity and calibration capabilities of this one make it intriguing.

Pressure Gauge Built In A Vacuum

Necessity might be the mother of all invention, but we often find that inventions around here are just as often driven by expensive off-the-shelf parts and a lack of willingness to spend top dollar for them. More often than not, we find people building their own tools or parts as if these high prices are a challenge instead of simply shrugging and ordering them from a supplier. The latest in those accepting the challenge of building their own parts is [Advanced Tinkering] who needed a specialty pressure gauge for a vacuum chamber.

In this specific case, the sensor itself is not too highly priced but the controller for it was the deal-breaker, so with a trusty Arduino in hand a custom gauge was fashioned once the sensor was acquired. This one uses an external analog-to-digital converter to interface with the sensor with 16-bit resolution, along with some circuitry to bring the ~8 V output of the sensor down to the 5 V required by the microcontroller. [Advanced Tinkering] wanted a custom live readout as well, so a 3D printed enclosure was built that includes both an LCD readout of the pressure and a screen with a graph of the pressure over time.

For anyone else making sensitive pressure measurements in a vacuum chamber, [Advanced Tinkering] made the project code available on a GitHub page. It’s a great solution to an otherwise overpriced part provided you have the time to build something custom. If you’re looking for something a little less delicate, though, take a look at this no-battery pressure sensor meant to ride along on a bicycle wheel.

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Fluke DMM Hack Adds One Digit To Model Number

Among his many interests, [Dave Jones] likes test and measurement equipment. He recently posted a few videos on his EEVblog exploring the reasons why Fluke voltmeters are so expensive. In the process, he stumbled upon an interesting hack for the Fluke 77.

The Fluke 77 was introduced in 1983, and is an average responding meter in the AC modes. This model has become a de-facto standard for use in maintenance depots and labs for equipment which has very long lifespans — think military and industrial gear, for example. Many test procedures and training materials have been designed around the use of the the Fluke 77. The cost to change them when a new and better meter comes along is usually so prohibitive they might as well be cast in stone — or at least hammered into 20 pound fanfold paper by a WordStar-driven daisy-wheel printer. But for those unburdened by such legacy requirements, Fluke has the 17x series of True RMS reading meters from since the beginning of this century. These meters bear a strong visual resemblance to their siblings in the 7x family and are substantially interchangeable but for their AC measurement methods. Continue reading “Fluke DMM Hack Adds One Digit To Model Number”

Laser Z-Axis Table Comes Into Focus

Laser cutters and 3D printers are game-changing tools to have in the workshop. They make rapid prototyping or repairs to existing projects a breeze as they can churn out new parts with high precision in a very short amount of time. The flip side of that, though, is that they can require quite a bit of maintenance. [Timo] has learned this lesson over his years-long saga owning a laser cutter, although he has attempted to remedy most of the problems on his own, this time by building a Z-axis table on his own rather than buying an expensive commercial offering.

The Z-axis table is especially important for lasers because a precise distance from the lens to the workpiece is needed to ensure the beams’s focal point is correctly positioned. Ensuring this distance is uniform over the entire bed can be a project all on its own. For this build, [Timo] started by building a simple table that allowed all four corners to be adjusted, but quickly moved on to a belt-driven solution that uses a stepper motor in order to adjust the entire workspace. The key to the build was learning about his specific laser’s focal distance which he found experimentally by cutting a slot in an angled piece of wood and measuring the height where the cut was the cleanest.

After everything was built, [Timo] ended up with a Z-axis table that is easily adjustable to the specific height required by his laser. Having a laser cutter on hand to bootstrap this project definitely helped, and it also seems to be an improvement on any of the commercial offerings as well. This also illustrates a specific example of how a laser cutter may be among the best tools for prototyping parts and building one-off or custom tools of any sort.

Precise Sundial Tells Time To The Minute

We’re always a fan of an interesting or unique clock build around here, which often use intricate pieces of technology to keep time such as weights and gears, crystal oscillators, or even a global network of satellites in the case of GPS. While these are all interesting methods of timekeeping, the original method of tracking the sun is often forgotten. With this clock, the sun is the main method of keeping track of time, but unlike traditional sundials it has a number of advancements that let it keep surprisingly accurate time. (Google Translate from German)

While most sundials can only show hours, this one from [leon andré], a retired physicist, has a method for displaying minutes as well. It uses pinholes instead of shadows to keep track of the position of the sun, with the pinhole casting a bright spot of sunlight onto a diagram below. The diagram keeps track of the minutes, and consists of curved lines which help account for the sun’s changing path throughout a typical year. The dial keeps track of local solar time, as any sundial would, but by rotating it along its vertical axis it can be calibrated for the timezone that it’s in regardless of its position.

As far as clock builds go, one that is completely passive like this semi-digital sundial is fairly unique, especially for its accuracy. And, when set to local solar time, it will be the most reliable method of keeping time long-term than possibly any other clock we’ve seen before, as long as it’s not too cloudy outside. On the other hand, it is possible to augment a sundial with some modern technology as well.

Thanks to [Adrian] for the tip!