The Negative Rail Explained

November 9, 2018 by Tom Nardi 45 Comments

With the high availability of modular components and incredible wealth of information and tutorials online, it’s now easier than ever for hackers and makers to assemble complex electronic projects without getting bogged down with the theory behind it all. But the downside is that the modern electronic hobbyist often doesn’t have as deep an understanding of the low-level concepts that they would have if they had to build everything from scratch. This can be a problem when they try diagnosing and repairing faults, or when they start to branch out into reverse engineering.

Which makes “Building Blocks” by [David Christensen] a very compelling series. Every week he will be demonstrating a new circuit on his blog, complete with a plain English explanation of how and why it’s used. In this first installment of the series, he’s tackling a concept most of us have seen when poking around in more complex electronic devices, but maybe never really gave much thought to: the negative rail.

What exactly is the negative rail, anyway? It’s pretty easy to understand the positive rail in a circuit and its relation to ground; even multiple positive rails, such as in devices which use both 5 V and 3.3 V, are simple enough to wrap your head around. Unfortunately when something drops below that logical 0V reference, it isn’t quite as intuitive. But as [David] explains, the negative rail in a circuit is critical for dealing with bipolar signals, such as audio, which ride above and below the 0 V center point.

[David] goes over a few methods used to create the negative rail, from the classic center-tap transformer to using a buck-boost converter. But not content with just describing how these circuits work, he walks the reader through the creation of a charge pump circuit that you can drop into your next project if you find yourself in need of the elusive voltage. After explaining and diagramming it, he builds the circuit on a scrap piece of copper clad board and puts it through some benchmarks to prove it matches the theory he laid out.

If you’re in the mood for more negative talk, check out the battle our very own [Steven Dufresne] had with voltages of varying polarity when building his BB-8 robot.

Lightsaber Uses Pogo Pins To Make Assembly A Breeze

November 7, 2018 by Kerry Scharfglass 9 Comments

There was an endless supply of fantastic projects at Supercon this year, but one whose fit and finish really stood out was [Scott]’s lightsaber. If you were walking around and saw someone with a very bright RGB device with a chromed-out handle hanging off their belt it was probably this, though it may have been hard to look at directly. On the outside, the saber looks like a well-polished cosplay prop, and it is! But when Scott quickly broke down the device into component pieces it was apparent that extra care had been put into the assembly of the electronics.

Like any good lightsaber replica the blade is lit, and wow is it bright. The construction is fairly simple, it’s a triplet of WS2812B LED strips back to back on a triangular core, mounted inside a translucent polycarbonate tube with a diffuser. Not especially unusual. But the blade can be popped off the hilt at a moments notice for easy transport and storage, so the strips can’t be soldered in. Connectors would have worked, but who wants flying wires when they’re disconnecting their lightsaber blade. The answer? Pogo pins! Scott runs the power, ground, and data lines out of the strips and into a small board with slip ring-style plated rings. On the hilt, there is a matching array of pogo pins to pass along power and data. The data lines from all the strips are tied together minimizing the number of connections to make, and the outer two power rings have more than one pin for better current-carrying capacity. A handy side effect is that there is nowhere on the blade where there aren’t LEDs; the strips go down to the very end of the blade where it meets the main board inside the hilt.

The hilt is filled with an assembly of 18650’s and a Teensy mounted with a custom shield, all fit inside a printed midframe. The whole build is all about robust design that’s easy to assemble. The main board is book-ended by perpendicular PCBs mounted to the ends, one at the top to connect to the blade and one at the bottom to connect to a speaker. Towards the bottom there is space for an optional Bluetooth radio to allow remote RGB control.

Scott is selling this as a product but also provides detailed instructions and parts lists for each component. Assembly instructions for the blade are here. The hilt is here. And pogo adapters are on OSH Park here. An overview of the firmware with links to GitHub is here. Check out a walkthrough of the handle assembly and blade attachment after the break!

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Making PCBs With A Cutting Plotter

October 28, 2018 by Maya Posch 26 Comments

[LudwigLabs] is creating PCBs using copper foil and a cutting plotter (vinyl cutter). In this approach, it’s an additive process where instead of removing copper from a copper-clad board, the traces are cut out of copper foil and transferred to a solid backing surface (cardboard, fiberglass, etc.).

While similar to the use of copper tape laid out by hand, as covered by us last year, the big advantage of using a cutting plotter is that it allows one to create much more complicated traces similar to those you would expect to see on a factory-made PCB. Since cutting plotters translate a 2D design into very precise movements of the cutting blade, this allows for sharp angles and significantly thinner traces, allows designs from EDA software like KiCad or Altium to be quickly translated to physical boards.

Enterprising hackers might consider the possibility of using this approach to make two-sided, and even multi-layered boards. The copper is produced separately from the substrate which opens up the potential for using uncommon materials like glass or paper to host the circuits. The main limitations are the transferring of (very delicate) copper structures and creating vias without damaging the traces.

As a comparison with traditional PCB fab processes, the photo exposure and etching (or laser exposure and etching) process requires the creation of masks, UV exposing a board, etching, cleaning and so on. The simplicity of copper foil traces has led to many experimenting with this approach. Would you want to use this additive process, or are there refinements or alterations you would make?

Transistor Fundamentals Animated

September 2, 2018 by Al Williams 5 Comments

When we were in school, every description of how transistors work was pretty dry and had a lot of math involved. We suppose you might have had a great instructor who was able to explain things more intuitively, but that was luck of the draw and statistically unlikely. These days, there are so many great videos on the Internet that explain things that even if you know the subject matter, it is fun to watch and see some of the great animations. For example [Sabin] has this beautifully animated explanation of how MOSFETs work that you can see below.

It uses the same basic graphics and style as his earlier video on bipolar transistors (second video, below) which is a great one to watch, too. In all fairness to your electronics teacher, the kind of graphics in these videos would have cost a fortune to do back in the 20th century — just watch some of the videos we talk about in some of our historical posts.

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OpenSCAD Handles The Math In 3D Printed Holder For Magnetic Spheres

August 28, 2018 by Donald Papp 35 Comments

3D printed holder mounted to bike wheel, fitting precisely 38 magnetic spheres around its perimeter. Tedious math? Not if you make OpenSCAD do it.

Off-the-shelf components are great; the world and our work simply wouldn’t be the same without. But one of the constraints is that one has to design around them, and that’s what led [Antonio Ospite] to create a parametric design in OpenSCAD for a 3D printed holder which snugly fits a number of magnetic spheres around its diameter.

If that sounds a bit esoteric, it will become much clearer in the context of [Antonio]’s earlier work in making a DIY rotary encoder out of a ring of magnetic spheres. He found that such a ring in front of two Hall effect sensors was low in cost, high in precision, and thanks to 3D printing it also had a lot of potential for customizing. But hampering easy design changes was the need for the spheres to fit snugly around whatever shape was chosen for the hardware, which meant constraints on the encoder diameter.

In this case, [Antonio] wished to create an encoder that could be attached to a bicycle wheel but needed to know what outer diameter would best fit a ring of magnetic balls perfectly, given that the balls were each 5 mm. OpenSCAD did the trick, yielding a design that fit the bike wheel and spokes while perfectly nestling 38 magnetic balls around the outside edge with a minimum of wasted space.

OpenSCAD is a CAD program that’s really more like a programming language than anything else. For those who are not familiar with it, [Brian Benchoff] walked through how to make a simple object in OpenSCAD, and [Elliot] has sung the praises of a few advanced functions. Now that this project makes DIY encoders easier, perhaps they could be used to add intuitive new controls to OpenSCAD itself.

How To Mash Up BLE, NodeJS, And MQTT To Get Internet Of Things

August 24, 2018 by Inderpreet Singh 10 Comments

We’re living in the world of connected devices. It has never been easier to roll your own and implement the functionality you actually want, rather than live with the lowest common denominator that the manufacture chose.

In a previous article I walked though a small python script to talk to a BLE light and used it to cycle through some colors. Now I want to delve deeper into the world of Internet Connected BLE devices and how to set up a simple Internet-Of-Things light. With this example in hand the sky’s the limit on what you can build and what it will be able to do.

Join me after the break as I demonstrate how to use NodeJS to bridge the digital world with the physical world.

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Simple ESP8266 Weather Station Using Blynk

August 20, 2018 by Tom Nardi 11 Comments

Today’s hacker finds themself in a very interesting moment in time. The availability of powerful microcontrollers and standardized sensor modules is such that assembling the hardware for something like an Internet-connected environmental monitor is about as complex as building with LEGO. Hardware has become elementary in many cases, leaving software as the weak link. It’s easy to build the sensor node to collect the data, but how do you display it in a useful and appealing way?

This simple indoor temperature and humidity sensor put together by [Shyam Ravi] shows one possible solution to the problem using Blynk. In the video after the break, he first walks you through wiring the demonstration hardware, and then moves on to creating the Blynk interface. While it might not be the ideal solution for all applications, it does show you how quickly you can go from a handful of components on the bench to displaying useful data.

In addition to the NodeMCU board, [Shyam] adds a DHT11 sensor and SSD1306 OLED display. He’s provided a wiring diagram in the repository along with the Arduino code for the ESP8266, but the hardware side of this demonstration really isn’t that important. You could omit the OLED or switch over to something like a BME280 sensor if you wanted to. The real trick is in the software.

For readers who haven’t played with it before, Blynk is a service that allows you to create GUIs to interact with microcontrollers from anywhere in the world. The code provided by [Shyam] reads the humidity and temperature data from the DHT11 sensor, and “writes” it to the Blynk service. From within the application, you can then visualize that data in a number of ways using the simple drag-and-drop interface.

We’ve seen Blynk and ESP8266 used to control everything from mood lighting to clearance-rack robotic toys. It’s a powerful combination, and something to keep in mind next time you need to knock something together in short order.

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