Author: Al Williams

4502 Articles

PLCs In Your Browser

December 6, 2017 by 31 Comments

If your usual tools are the Arduino and the Raspberry Pi, you might find it surprising that the industrial world tends to run on Programmable Logic Controllers, or PLCs. You can think of a PLC as a very rugged industrial Arduino, but it’s best not to take that analogy too far. Some PLCs are very simple and some are quite complex, but one thing they do have in common is they are usually programmed using ladder logic. If you’ve ever wanted to learn how to program PLCs — a very marketable job skills in some places — you can now build and simulate ladder logic in your browser. [Garry Shortt] has a video walkthrough of the tool, that you can see below.

If you are used to conventional programming, you may find ladder logic a little frustrating. Originally, it was a documentation tool for relay logic but has grown to handle modern cases. It may actually help you to not think of it so much as a programming language, instead as a tool for drawing relay schematics. Contacts can be normally open or closed and in series or parallel to form AND and OR gates, for example, while coils can activate contacts.

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When Is A 10-bit A/D An 8-bit A/D?

December 6, 2017 by 25 Comments

Marketing guys love bigger numbers. Bigger is better, right? After all, Subway called it a “footlong” not an 11-incher. So when it comes to analog to digital (A/D) conversion, more bits are better, right? Well, that depends. It is easy to understand that an A/D will have a low and high measurement and the low will be zero counts and the high will result in the maximum count for the number of bits. That is, an 8-bit device will top out at 255, a 10-bit at 1023, and so on.

The question is: are those bits meaningful? The answer depends on a few factors. Like most components we deal with, our ideal model isn’t reality, but maybe it is close enough.

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EasyEDA Two Years Later

December 5, 2017 by 47 Comments

Some people want everything on the cloud, while others refuse to put even the smallest scrap of data on the Internet. Most of us fall somewhere in between. A few years ago, we talked about a few cloud-based PCB layout programs including one called EasyEDA. We were impressed because it was a full package: schematic capture, simulation, and PCB layout. It was free to use, although they would give you a quote for producing your boards, though you were under no obligation to buy them. Of course things change in two years, so if you are curious how EasyEDA is doing, [Yahya Tawil] posted an in-depth review.

Some of the new features include an autorouter and the ability to order parts from a BOM directly, not just PCBs. The cloud aspect is handy, not only because you don’t have to install and update software to use it anywhere, but because it is very natural to collaborate with others on projects. We did notice, though, that the autorouter can run in the cloud, or you can download and run it local because it apparently loads the server significantly.

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Current Measurement With Oscilloscopes

December 4, 2017 by 19 Comments

What do a Rogowski coil, a magnetic core, and a hall effect sensor have in common? They are all ways you can make oscilloscope probes that measure current. If you think of a scope as a voltage measurement device, you ought to watch the recent video from Keysight Technology (see below). It is true that Keysight would love to sell you a probe, but the video is not a sales pitch, just general technical information about making current measurements with an oscilloscope.

Of course, you can always measure the voltage across a shunt resistor — either one that is naturally in the circuit or one you’ve put inline just for measuring purposes. But if you add a resistor it will change the circuit subtly and it may have to handle a lot of power.

The Keysight video points out that there are different probes for different current measurement regimes. High current, medium current, and low current all use different probes with different technologies. The video is only about 6 minutes long and if you’ve never thought about measuring current with a scope, it is worth watching.

The video shares some high-level details of how the current probes work — that’s where the Rogowski coil comes in, for example. Of course, you can’t expect a vendor to tell you how to build your own current probes. That’s OK, though, because we will. Current probes are often expensive, but you can sometimes pick up a deal on a used one.

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Gesture Control For Lunch Money

December 3, 2017 by 16 Comments

[Dimitris Platis] wanted to add gesture control to his PC. You’d think that would be expensive, but by combining a diminutive Arduino, a breakout board with a gesture controller, and an interconnect PCB, he managed to pull it off for about $7. That doesn’t include the optional 3D-printed case and we think you could omit the interconnect board if you don’t mind some wires and further cut costs. [Dimitris] calls it Nevma, and you can see how the device works in the video below.

The heart of the project is a sensor that measures light and motion. The chip and the breakout board are just a couple of bucks if you order them from China. You can find them in the US if you don’t mind spending a little bit more. The device has an I2C interface, and [Dimitris] uses a tiny Mini SS Micro for the USB interface and the CPU.

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Just In Time For The Holidays: Give The Gift Of Cray

December 2, 2017 by 24 Comments

The name Cray, as in [Seymour Cray] is synonymous with supercomputing. If you hurry, you can bid on a Cray J90/J916 on eBay. You might want to think about where to put it though. It is mounted on a trailer, requires 480V, and the shipping is $3,000!

First introduced in 1994, the J90 was an “entry level” machine. This particular machine supported up to 16 CPUs (each CPU was actually two chips) running at a blazing 100 MHz. The memory system was more impressive, achieving 48 GB/s.

The Cray T90 computer was much faster (and more expensive) but none of these computers had the performance of a typical PC’s graphics card these days. Even your phone may have more raw computing power, depending on how you choose to measure. Don’t fear, though. Cray Research still makes supercomputers that can eat your phone for lunch.

Still, at the time, this was big iron. The I/O system used SPARC processors that would have been entire workstations in that era. The eBay listing says it might need a little work — we weren’t clear if the seller meant in general or just the cooling system, but you can assume this is a fixer-upper. Apparently, the Retro-Computing Society of Rhode Island restored a similar beast so it can be done.

If your holiday budget doesn’t have room for a real supercomputer, here’s one that is 1/10 the size and much less expensive. Or, you could just pretend.

Lisp In 200 Lines

December 2, 2017 by 16 Comments

Contrary to popular belief, LISP does not stand for “lots of irritating spurious parenthesis.” However, it is true that people tend to love or hate this venerable programming language. Whichever side of the fence you’re on, many of the ideas it launched decades ago have become staples of other newer languages. How much C code do you think it takes to make a functional LISP system? If you guessed more than 200, you’ll want to go look at this GitHub repository.

Actually, the code isn’t as good as the (sort of) literate programming white paper on the program, but it gives a good overview of how 200 lines of C code can produce a working LISP-like language good enough to create its own eval loop. It does lack memory handling and error detection, so if you really wanted to use it, you’d probably need to spruce it up a bit.

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