Here’s The Norwegian Tape Deck Teardown You’ve Been Waiting For

May 15, 2024 by 37 Comments

“They just don’t build ’em like they used to” is a truer statement every year. Whether your vice is CRTs, film cameras, or tape decks, you’ll know that the very best gear simply isn’t manufactured anymore. Even the day-to-day stuff from 60 years ago is often a cut above a lot of today’s equipment. [Anthony Kouttron] shows us this with his teardown of a Tandberg TCD301 from many decades ago.

The Tandberg unit is beautifully finished in wood and metal, a style of construction that’s fairly rare these days. It’s got big, chunky controls, and a certain level of heft that is out of vogue in modern electronics. Heavy used to mean good — these days, it means old. That’s not to say it’s indestructible, though. It’s full of lots of old plastic pulleys and fasteners that have aged over the decades, so it’s a little fragile inside.

Still, [Anthony] gives us a great look at the aluminium chassis and buttons and the electromechanical parts inside. It’s a rats-nest design with lots of discrete components and wires flying between boards. You couldn’t economically produce this and sell it to anyone today, but this is how it was done so many years ago.

This non-functional unit ended up being little more than a salvage job, but we’re still glad that [Anthony] gave us a look inside. Still, if you long for more cassette-themed teardowns, we’ve got the goodness you’re looking for!

A Slice Of Simulation, Google Sheets Style

May 15, 2024 by 6 Comments

Have you ever tried to eat one jelly bean or one potato chip? It is nearly impossible. Some of us have the same problem with hardware projects. It all started when I wrote about the old bitslice chips people used to build computers before you could easily get a whole CPU on a chip. Bitslice is basically Lego blocks that build CPUs. I have always wanted to play with technology, so when I wrote that piece, I looked on eBay to see if I could find any leftovers from this 1970-era tech. It turns out that the chips are easy to find, but I found something even better. A mint condition AM2900 evaluation board. These aren’t easy to find, so the chances that you can try one out yourself are pretty low. But I’m going to fix that, virtually speaking.

This was just the second potato chip. Programming the board, as you can see in the video below, is tedious, with lots of binary switch-flipping. To simplify things, I took another potato chip — a Google Sheet that generates the binary from a quasi-assembly language. That should have been enough, but I had to take another chip from the bag. I extended the spreadsheet to actually emulate the system. It is a terrible hack, and Google Sheets’ performance for this sort of thing could be better. But it works.

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Introduction To MOSFET Switching Losses

May 15, 2024 by 17 Comments

Metal-oxide semiconductor field-effect transistors (MOSFETs) see common use in applications ranging from the very small (like CPU transistors) to very large (power) switching applications. Although its main advantage is its high power efficiency, MOSFETs are not ideal switches with a perfect on or off state. Understanding the three main sources of switching losses is crucial when designing with MOSFETs, with a recent All About Circuits article by [Robert Keim] providing a primer on the subject.

As it’s a primer, the subthreshold mode of MOSFET modes of operation is omitted, leaving the focus on the linear (ohmic) mode where the MOSFET’s drain-source is conducting, but with a resistance that’s determined by the gate voltage. In the saturated mode the drain-source resistance is relatively minor (though still relevant), but the turn-on time (RDS(on)) before this mode is reached is where major switching losses occur. Simply switching faster is not a solution, as driving the gate incurs its own losses, leaving the circuit designer to carefully balance the properties of the MOSFET.

For those interested in a more in-depth study of MOSFETs in e.g. power supplies, there are many articles on the subject, such as this article (PDF) from Texas Instruments.

Custom Polyurethane Belts Made Easy

May 15, 2024 by 11 Comments

If you need to make polyurethane belts in custom lengths, it’s not too hard. You just need to take lengths of flexible polyurethane filament, heat the ends, and join them together. In practice, it’s difficult to get it right by hand. That’s why [JBVCreative] built a 3D printed jig to make it easy. 

The jig consists of two printed sliders that mount on a pair of steel rods. Each slider has a screw-down clamp on top. The clamps are used to hold down each end of the polyurethane filament to be joined. Once installed in the jig, the ends of the filament can be heated with a soldering iron or other element. and then gently pushed together. The steel rods simply enable the filament to be constrained linearly so the ends don’t shift during the joining process.

The jig doesn’t produce perfect belts. There’s still a small seam at the join that is larger than the filament’s base diameter. A second jig for trimming the belt to size could be helpful in this regard. Still, it’s a super useful technique for making custom belts. This could be super useful to anyone needing to restore old cassette decks or similar mechanical hardware.

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BreadboardOS, A Command Line Interface For The Pico

May 14, 2024 by 22 Comments

Operating systems! They’re everywhere these days, from your smart TV to your smartphone. And even in your microcontrollers! Enter BreadboardOS for the Raspberry Pi Pico.

BreadboardOS is built on top of FreeRTOS. It’s aim is to enable quick prototyping with the Pi Pico. Don’t confuse operating system with a graphical environment — BreadboardOS is command-line based. You’d typically interface with it via a serial terminal emulator, but joy of joys, it does support color!

Using BreadboardOS is a little different than typical microcontroller development. Creating an application involves adding a “service” which is basically a task in FreeRTOS parlance. The OS handles running your service for you. Via the text interface, you can query running services, and start or kill them at will.

Meanwhile, running df will happily give you stats on the flash usage of the Pi Pico, and free will tell you how full the memory is doing. If you really want to get raw, you can make calls to control GPIO pins, the SPI hardware, or other peripherals, and do it right on the command line.

BreadboardOS isn’t for everyone, but it could prove a useful tool if you like that way of doing things. It’s not the only OS out there for the Pi Pico, either!

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The Perfect Desktop Kit For Experimenting With Self Driving Cars

May 14, 2024 by 1 Comment

When we think about self-driving cars, we normally think about big projects measured in billions of dollars, all funded by major automakers. But you can still dive into this world on a smaller scale, as [jmoreno555] demonstrates.

The build consists of a small RC car—an HSP 94123, in fact. It’s got a simple brushed motor inside, driven by a conventional speed controller, and servo-driven steering. A Raspberry Pi 4 is charged with driving the car, but it’s not alone. It’s outfitted with a Google Coral USB stick, which is a machine learning accelerator card capable of 4 trillion operations per second. The car also has a Wemos D1 onboard, charged with interfacing distance sensors to give the car a sense of its environment. Vision is courtesy of a 1.2-megapixel camera with a 160-degree lens, and a stereoscopic camera with twin 75-degree lenses. Software-wise, it’s early days yet. [jmoreno555] is exploring the use of Python and OpenCV to implement basic lane detection and other self driving routines, while using Blender as a simulator.

The real magic idea, though, is the treadmill. [jmoreno555] realized that one of the frustrations of working in this space is in having to chase a car around a test track. Instead, the use of a desktop treadmill allows the car to be programmed and debugged with less fuss in the early stages of development.

If you’re looking for a platform to experiment with AI and self-driving, this could be an project to dive in to. We’ve covered some other great builds in this space, too. Meanwhile, if you’ve cracked driving autonomy and want to let us know, our tipsline is always standing by!

Vibrating Braille Display Is Portable

May 14, 2024 by 5 Comments

Smartphones are an integral part of life, but what if you can’t see the screen? There is text-to-speech available, but that’s not always handy and can be slow. It also doesn’t help users who can’t hear or see. Refreshable braille devices are also available, but they are expensive and not very convenient to use. [Bmajorspin] proposed a different method and built a prototype braille device that worked directly with a cell phone. The post admits that as the device stands today, it isn’t a practical alternative, but it does work and is ripe for future development to make it more practical.

The device saves costs and increases reliability by using six vibration motors to represent the six dots of a braille cell. However, this leads to an important issue. The motor can’t directly mount to the case because you have to feel each one vibrating individually. A spring mounting system ensures that each motor only vibrates the tactile actuator it is supposed to. However, the system isn’t perfect, and fast output is difficult to read due to the spread of vibrations.

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