A Practical Look At Chokes For EMI Control

March 15, 2020 by 6 Comments

Radio frequency electronics can seem like a black art even to those who intentionally delve into the field. But woe betide the poor soul who only incidentally has to deal with it, such as when seeking to minimize electromagnetic interference. This primer on how RF chokes work to reduce EMI is a great way to get explain the theory from a practical, results-oriented standpoint.

As a hobby machinist and builder of machine tools, [James Clough] has come across plenty of cases where EMI has reared its ugly head. Variable frequency drives are one place where EMI can cause problems, and chokes on the motor phase outputs are generally prescribed. He used an expensive choke marketed as specific for VFD applications on one of his machines, but wondered if a cheap ferrite core would do the job just as well, and set to find out.

A sweep of some ferrite cores with a borrowed vector network analyzer proved unsatisfying, so [James] set up a simple experiment with a function generator and an oscilloscope. His demo shows how the impedance of a choke increases with the frequency of the test signal, which is exactly the behavior that you’d want in a VFD – pass the relatively low-frequency phase signals while blocking the high-frequency EMI. For good measure, he throws a capacitor in parallel to the choke and shows how much better a low-pass filter that makes.

We love demos like this that don’t just scratch an intellectual itch but also have a practical goal. [James] not only showed that (at least in some cases) a $13 ferrite can do the same job as a $130 VFD choke, but he showed how they work. It’s basic stuff, but it’s what you need to know to move on to more advanced RF filter designs.

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Rover Runs Slow And Steady On Solar Power

March 15, 2020 by 11 Comments

The solar panel technology we have available today doesn’t really lend itself to practical everyday transport. But when speed isn’t a concern, it can make for some very interesting autonomous rovers. One example of this is [Daniel Riley] aka [rctestflight]’s solar powered rover, which he built to live autonomously at his flight testing field, crawling around whenever it has gathered enough juice from the sun.

[Daniel] has thing for autonomous craft of all types, with quite a few aircraft and boats to his name. This rover is built around a welded steel frame, with each wheel driven by a brushless geared motors via a chain. While it’s technically a skid steer, the electronic speed controls are from a quadcopter and can’t reverse, so it doesn’t turn quite on the spot.

With the rigid steel frame, any small bump in the ground would cause one wheel to lose traction. To fix this, the frame was cut in two and a pivot added in the center, allowing all four wheels to always remain on the ground. Another problem is that the wheels would sometimes dig themselves into the soft wet ground, so this, [Daniel] attached a 3D printed “hump” to each drive wheel, which helps them to climb out of any soft spots. For the next version of this rover, [Daniel] plans to use cheap DC geared motors from a Barbie jeep. They’re a bit too fast though, so he’ll be adding 3D printed cycloidal reduction gearboxes. We’re definitely looking forward to seeing here this project goes from here.

There have been a number of projects to test solar powered robots for agricultural use. We really like the idea, with its potential for long duration missions. Imagine something like this roaming the Black Rock playa in the US, the Makgadikgadi Pan in Botswana, or even the Sahara Desert, while gathering environmental data and making awesome time-lapse videos.

Digital Designer Teaches High School

March 15, 2020 by 6 Comments

We wish we had met [Mr. Mueller] when we were in high school. After 20 years as a digital design engineer, he decided to teach a digital electronics class at the high school level at LASA high school in Austin, Texas. He’s been doing it for seven years and has made his course material available via Google Docs.

Don’t let the high school level fool you. Topics range from simple electronics to Spice. There’s coverage of discrete devices, oscilloscopes, and Arduinos. There’s plenty of digital logic, of course, and a simple 16-bit microprocessor, too. There are labs for FPGAs using Verilog and talks about ARM. It’s pretty comprehensive and we wonder if they can really cram all this into a single school year. One thing we saw that caught our eye was the simulation of a transistor using Play-Doh. Turns out it isn’t an electrical simulation, but a simulation of how photolithography creates transistors. Still good stuff.

This would be great for teaching students of pretty much any age, even if you took only parts of it. It would also be worthwhile for self-study. We know how much work it takes to put something like this together, and we can’t commend [Mr. Mueller] and the LASA high school enough for making it available to everyone.

There is more and more course material out there at all levels and we think that’s a great thing. If you need something for a younger set, try a blindfold.

Powering Neon With A Joule Thief

March 14, 2020 by 10 Comments

Joule thief are small, fun circuits which exploit a few characteristics of electronics and LEDs in order to “steal” virtually all of the energy stored in a battery. They can operate at incredibly small voltages and are fairly simple to make. With a few modifications to this basic circuit it’s possible to drive other things than an LED, though, like this joule thief that lights up a neon bulb.

The circuit from [suedbunker] aka [fuselage] is based on a pin from the Chaos Communication Camp which had a standard LED. To get a neon light to illuminate a few modifications to the standard joule thief are needed.

First, the windings have to be changed from 10:10 to 10:80 to increase the voltage across the bulb. Second, a transistor with slightly different characteristics was used than the original design. The capacitor was also replaced with a larger one.

While it might seem simple, the physics of how a joule thief works are anything but, and modifying the delicate circuit to work with something other than an LED is commendable. It also has a steampunk vibe which is a cool look even in projects that don’t involve steam at all.

Get Your Weather Images Straight From The Satellite

March 14, 2020 by 15 Comments

[Josh] has a series called Ham Radio Crash Course and a recent installment covers how you can grab satellite images directly from weather satellites. This used to be more of a production than it is now thanks to software defined radio (SDR). Josh also has another project using a 3D printer to make an antenna suitable for the job. You can see the video below.

The software is the venerable WXtoImg program. This is abandonware, but the community has kept the software available. The program works on Linux, Windows, and Mac. The satellites in question operate around 137 MHz, but that’s easily in the range of even the cheap SDR dongles. [Josh] shows how to use a virtual audio cable on Windows to connect the output of the radio to the input of the WXtoImg program. Under Linux, you can do this with Pulse or Jack very easily without any extra hardware.

There’s some setup and calibration necessary for the software. You’ll also need the current orbital data and the program will tell you when you can find the next satellite passing overhead. Generally speaking you’ll want your antenna outside, which [Josh] solved by taking everything outdoors and having some lunch during the pass. It also takes some time to post-process the data into images and audio.

We know this isn’t new. But we did like [Josh’s] clear and up-to-date guide. We remember watching NOAA 15 as it started to lose its electronic mind.

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Manual To Hydraulic Press, With A Paint Sprayer

March 14, 2020 by 11 Comments

A press can be one of the most useful additions to a workshop, once you have one you will wonder how you ever coped beforehand when it came to all manner of pressing in and pushing out tasks. An arbor press with a big lever and ratchet is very quick to use, while a hydraulic press  gives much higher pressure but is extremely slow. [The Buildist] missed out on an arbor press, so turned his eye to improving the speed of his hydraulic one. The solution came from an unexpected source, an airless paint sprayer that had come his way because its valves were gummed up with paint.

An airless paint sprayer is simply a high pressure pump that supplies paint to a nozzle, and that pump is easily repurposed to pump oil instead of paint. Testing revealed it could produce a pressure of 3000 PSI, which would be plenty to move the hydraulic jack even if the hand pump would be needed to finish the job when higher force was required.

What follows over two videos is a masterclass in hydraulic jacks, as he strips down the jack from his press, and modifies it not only to take an input from the pump, but also to run inverted by the addition of an oil reservoir pick-up pipe. Along the way we learn a few useful gems such as the fact that a grease gun pipe is the same as a hydraulic pipe, but much cheaper.

The result is a jack that extends quickly, and has the pressure to do most pressing tasks without the hand assistance. He crushes a drinks can for effect, then pinches the end of a piece of pipe, because given a press, why wouldn’t you! Take a look at both videos below the break.

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The Ultimate Game Boy Talk

March 14, 2020 by 3 Comments

It is absolutely no exaggeration to say that [Michael Steil] gave the Ultimate Game Boy talk at the 33rd Chaos Communication Congress back in 2016. Watch it, and if you think that there’s been a better talk since then, post up in the comments and we’ll give you the hour back. (As soon as we get this time machine working…)

We were looking into the audio subsystem of the Game Boy a while back, and scouring the Internet for resources, when we ran across this talk. Not only does [Michael] do a perfect job of demonstrating the entire audio system, allowing you to write custom chiptunes at the register level if that’s your thing, but he also gets deep into the graphics engine. You’ll never look at a low-bit Pole Position clone the same again. The talk even includes some new (in 2016, anyway) hacks on the pixel pipeline in the last 15 minutes, and a quick review of the hacking tools and even the Game Boy camera.

Why do you care about the Game Boy? It’s probably the last/best 8-bit game machine that was made in mass production. You can get your hands on one, or a clone, for dirt cheap. And if you build a microcontroller-based cartridge, you can hack the whole thing non-destructively live, and in Python! Or emulate the whole shebang. Either way, when you’re done, you’ve got a portable demo of your hard work thanks to the Nintendo hardware. It makes the perfect retro project.

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