Buttery Smooth Fades With The Power Of HSV

June 18, 2018 by Kerry Scharfglass 20 Comments

In firmware-land we usually refer to colors using RGB. This is intuitively pleasing with a little background on color theory and an understanding of how multicolor LEDs work. Most of the colorful LEDs we are use not actually a single diode. They are red, green, and blue diodes shoved together in tight quarters. (Though interestingly very high end LEDs use even more colors than that, but that’s a topic for another article.) When all three light up at once the emitted light munges together into a single color which your brain perceives. Appropriately the schematic symbol for an RGB LED without an onboard controller typically depicts three discrete LEDs all together. So it’s clear why representing an RGB LED in code as three individual values {R, G, B} makes sense. But binding our representation of color in firmware to the physical system we accidentally limit ourselves.

Last time we talked about color spaces, we learned about different ways to represent color spatially. The key insight was that these models called color spaces could be used to represent the same colors using different groups of values. And in fact that the grouped values themselves could be used to describe multidimensional spacial coordinates. But that post was missing the punchline. “So what if you can represent colors in a cylinder!” I hear you cry. “Why do I care?” Well, it turns out that using colorspace can make some common firmware tasks easier. Follow on to learn how!

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Getting Good At FPGAs: Real World Pipelining

June 12, 2018 by Al Williams 16 Comments

Parallelism is your friend when working with FPGAs. In fact, it’s often the biggest benefit of choosing an FPGA. The dragons hiding in programmable logic usually involve timing — chaining together numerous logic gates certainly affects clock timing. Earlier, I looked at how to split up logic to take better advantage of parallelism inside an FPGA. Now I’m going to walk through a practical example by modeling some functions. Using Verilog with some fake delays we can show how it all works. You should follow along with a Verilog simulator, I’m using EDAPlayground which runs in your browser. The code for this entire article is been pre-loaded into the simulator.

If you’re used to C syntax, chances are good you’ll be able to read simple Verilog. If you already use Verilog mostly for synthesis, you may not be familiar with using it to model delays. That’s important here because the delay through gates is what motivates us to break up a lot of gates into a pipeline to start with. You use delays in test benches, but in that context they mostly just cause the simulator to pause a bit before introducing more stimulus. So it makes sense to start with a bit of background on delays.

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Pipelining Digital Logic In FPGAs

June 5, 2018 by Al Williams 11 Comments

When you first learn about digital logic, it probably seems like it is easy. You learn about AND and OR gates and figure that’s not very hard. However, going from a few basic gates to something like a CPU or another complex system is a whole different story. It is like going from “Hello World!” to writing an operating system. There’s a lot to understand before you can make that leap. In this set of articles, I want to talk about a way to organize more complex FPGA designs like CPUs using a technique called pipelining.

These days a complex digital logic system is likely to be on an FPGA. And part of the reason we can get fooled into thinking digital is simple is because of the modern FPGA tools. They hide a lot of complexity from you, which is great until they can’t do what you want and then you are stuck. A good example of that is where you are trying to hit a certain clock frequency. If you aren’t careful, you’ll get a complaint from the tool that you can’t meet timing constraints.

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Optocouplers: Defending Your Microcontroller, MIDI, And A Hot Tip For Speed

May 9, 2018 by Elliot Williams 65 Comments

Deep in the heart of your latest project lies a little silicon brain. Much like the brain inside your own bone-plated noggin, your microcontroller needs protection from the outside world from time to time. When it comes to isolating your microcontroller’s sensitive little pins from high voltages, ground loops, or general noise, nothing beats an optocoupler. And while simple on-off control of a device through an optocoupler can be as simple as hooking up an LED, they are not perfect digital devices.

But first a step back. What is an optocoupler anyway? The prototype is an LED and a light-sensitive transistor stuck together in a lightproof case. But there are many choices for the receiver side: photodiodes, BJT phototransistors, MOSFETs, photo-triacs, photo-Darlingtons, and more.

So while implementation details vary, the crux is that your microcontroller turns on an LED, and it’s the light from that LED that activates the other side of the circuit. The only connection between the LED side and the transistor side is non-electrical — light across a small gap — and that provides the rock-solid, one-way isolation.

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How To Build Anything Out Of Aluminum Extrusion And 3D Printed Brackets

May 8, 2018 by Roger Cheng 42 Comments

The real power of 3D printing is in infinite customization of parts. This becomes especially powerful when you combine 3D printing with existing materials. I have been developing a few simple tricks to make generic fasteners and printed connectors a perfect match for aluminum extrusion, via a novel twist or two on top of techniques you may already know.

Work long enough with 3D printers, and our ideas inevitably grow beyond our print volume. Depending on the nature of the project, it may be possible to divide into pieces then glue them together. But usually a larger project also places higher structural demands ill-suited to plastic.

Those of us lucky enough to have nice workshops can turn to woodworking, welding, or metal machining for larger projects. Whether you have that option or not, aluminum extrusion beams provide the structure we need to go bigger and to do it quickly. And as an added bonus, 3D printing can make using aluminum extrusion easier and cheaper.

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Printed It: Toolbag Essentials

May 7, 2018 by Tom Nardi 26 Comments

While complex devices assembled from 3D printed components are certainly impressive, it’s the simple prints that have always held the most appeal to me personally. Being able to pick an object up off the bed of your printer and immediately put it to use with little to no additional work is about as close as we can get to Star Trek style replicators. It’s a great demonstration to show off the utility of your 3D printer, but more importantly, having immediate access to some of these tools and gadgets might get you out of a jam one day.

With that in mind, I thought we’d do things a little differently for this installment of Printed It. Rather than focusing on a single 3D model, we’ll be taking a look at a handful of prints which you can put to practical work immediately. I started by selecting models based on the idea that they should be useful to the average electronic hobbyist in some way or another, and relatively quick to print. Each one was then printed and evaluated to determine its real-world utility. Not all made the grade.

Each model presented here is well designed, easy to print, and most critically, legitimately useful. I can confidently say that each one has entered into my standard “bag of tricks” in some capacity, and I’m willing to bet a few will find their way into yours as well.

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Biasing That Transistor: The Common Emitter Amplifier

May 4, 2018 by Jenny List 84 Comments

If you open up the perennial favourite electronics textbook The Art Of Electronics and turn to the section on transistors, you will see a little cartoon. A transistor is shown as a room in which “transistor man” stands watching a dial showing the base current, while adjusting a potentiometer that limits the collector current. If you apply a little more base current, he pushes up the collector a bit. If you wind back the base current, he drops it back. It’s a simple but effective way of explaining the basic operation of a transistor, but it stops short of some of the nuances of how a transistor works.

Of course the base-emitter junction is a diode and it is not a simple potentiometer that sits between collector and emitter. The “better” description of these aspects of the device fills the heads of first-year electronic engineering students until they never want to hear about an h-paramater or the Ebers-Moll model of transistor function again in their entire lives. Fortunately it is possible to work with transistors without such an in-depth understanding of their operation, but before selecting the components surrounding a device it is still necessary to go a little way beyond transistor man.

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