Weekly Elektor Wrap Up: An Innovative ECG Patch, an Affordable Linux Computer, & an AVR Software-Defined Radio Event

It’s time for our weekly wrap up of Elektor news and content for Circuit Cellar members. As usual, our colleagues in Europe and beyond are always covering some cool embedded-related topics.

Let’s start with an interesting post about an innovative processor-based healthcare system: an intelligent patch capable of continuously monitoring heart activity. The design combines embedded and wireless technologies to measure, record, and transmit electrocardiogram signals:

The patch developed by the research labs Imec and Holst Centre and the Danish company Delta measures 3 ECG signals while a 3D accelerometer monitors physical activity. The captured data is processed by a microprocessor integrated in the patch and relevant information is transmitted wirelessly using the new Bluetooth Low Energy technology. Energy consumption is low enough to allow continuous operation during one week.

Click here to read the entire post.

Have you been reading Circuit Cellar columnist Bob Japenga’s articles on embedded Linux? If so, you’ll check out Elektor’s post about Raspberry Pi:

The board is based on a Broadcom BCM2835 SoC, which includes an ARM1176JZF-S 700 MHz processor, a VideoCore IV GPU and 128 or 256 MB of RAM is intended to run Linux kernel based operating systems. Selling for only 28 Euros the distributors’ websites have been overwhelmed by the demand and the first batch of 10,000 pieces was sold out in less than an hour.

The foundation plans to release two versions: Model A & Model B. Model A will have 128 MB RAM, one USB port and no Ethernet controller, while model B will contain 256 MB RAM, two USB ports and a 10/100 Ethernet controller.

Click here for the entire article. You can also read my recent post on Raspberry Pi. Check it out!

Lastly, consider attending the upcoming Elektor Academy webinar “AVR Software Defined Radio.” The webinar is scheduled for 3/29/12. Click here for more information. If you attend, be sure to let us know what you think!

Circuit Cellar and CircuitCellar.com are part of the Elektor group.

Issue 261: Renesas RL78, Cap Touch, Synapse SNAP, & More!

Here’s a sneak peek at the projects and topics slated for the April issue of Circuit Cellar: Linux software development tools, DIY cap-touch, gain-controlled amplifier; color classification reader; start designing with the Renesas RL78 microcontroller; an introduction to sigma-delta modulators; RFI bypassing, with a focus on parallel capacitors; mesh networking simplified with SNAP technology; and more.


Clemens Valens introduces the Renesas Electronics RL78:

Click the image to link to the Renesas product page

Jeff Bachiochi takes a close look at Synapse Wireless SNAP technology:

Click the image to link to the Synapse-Wireless Kit webpage

Ed Nisley presents Part 2 of his article series “RFI Bypassing”:

The tracking generator output and spectrum analyzer input connect to adjacent PCB pads on the left of the SMD capacitor. Connecting the spectrum analyzer to the pad on the right side changes the measured self-resonant frequency.

The April issue will hit newsstands in late March.

Fundamental Amplifier Techniques with Electron Tubes

Want tips on designing electron tube amplifiers? Fundamental Amplifier Techniques with Electron Tubes might be the book for you. The author, Rudolf Moers carefully details the science of hollow-state design as applied to amplifiers and power supplies.

The book is an Elektor group publication. So, I asked tube amp aficionado Richard Honeycutt to provide an unbiased review the book. (I asked him to do this prior to taking him on as a columnist for audioXpress magazine.) He agreed, and here’s the review, which is also available in audioXpress April 2012:

Back in the 1950s and 1960s, if you wanted to learn about vacuum tube amplifiers, you could read the Radiotron Designer’s Handbook, a 1,500-page behemoth that covered all kinds of vacuum tube circuits that were known at the time, and also included abundant information on passive components as well. Or you could use the introductory material and example schematics in the RCA Receiving Tube Manual—much shorter and less expensive, and also far less comprehensive. Of course, it did include data on most tubes then being manufactured by RCA. If you just wanted to build your own amplifiers, but were not interested in designing, there was the Mullard  Circuits for Audio Amplifiers. For a more scholarly approach, you could check out an electrical engineering textbook such as Analysis and Design of Electronic Circuits by Paul Chirlian.

Now, however, things are different. Although some of these references can be found on the Internet, they are no longer up-to-date. Happily, however, Elektor recently published Fundamental Amplifier Techniques with Electron Tubes by Rudolf Moers, which presents a 21st-century perspective on the science of hollow-state design as applied to amplifiers and power supplies. Beginning with the principles of electron emission, the book progresses through standard vacuum tube varieties: diodes, triodes, tetrodes, and pentodes, after which it covers such general principles as frequency dependent behavior, non-linear distortion, noise, and negative feedback. The book concludes with a chapter on the construction of electron tube amplifiers. Unlike many of the earlier authors of books on electron tubes, Moers is not constrained by a need to cover such specialized tubes as pentagrid converters, or circuits specifically used in radio and TV receivers. Instead, he uses his 800 pages to discuss the physics underlying electron tube operation far more comprehensively than did any of his predecessors. He does this in a way that maximizes presentation of principles while minimizing unnecessary mathematics. In many cases, the physical explanations can be skipped over by those whose only interest is design methods. For the reader who does take advantage of the physical explanations, Moers’s inclusion of an eight-page listing/definition of mathematical symbols makes the explanations easy to follow.

The focus is by no means primarily on physics, however. None of the classic texts provides anything like so comprehensive coverage of the design and operation of half- and full-wave rectifier/filter circuits, or vacuum tube phase shifters, to mention a couple of examples.

Moers’s book assumes that the reader is familiar with basic DC and AC circuit theory, and therefore does not undertake the task of educating those who lack this understanding. The book is written from a scientific perspective in that, while mentioning the disconnect between measured and perceptual performance of an amplifier, the author makes no dogmatic claims about the relationship between the two, other than to opine that most of the “tube sound” results from harmonic distortion components that some people find pleasing to the ear. (Having followed this discussion for about four decades, your reviewer partially concurs, but believes that there are other elements involved as well.) The author lightheartedly introduces the quantity “cm2 of gooseskin/watt” as an example of a measurement of perceptual phenomena.

A consequence of Moers’ scientific approach is that specific catch phrases found in many amateur-oriented publications on tube technology are conspicuously absent. For example, it is difficult to read much about tube power amplifiers without noticing mention of the “Williamson amplifier.” This circuit was developed by D. T. N. Williamson and described in articles in Wireless World in April and May, 1947. It was unique in that it applied negative feedback around the entire amplifier, including the output transformer, thus reducing nonlinear distortion. Doing this required very careful design to ensure stability, including the elimination of interstage transformers such as the phase splitter transformer used in many prior designs.

Moers does not mention the Williamson amplifier by name, but the vacuum tube phase splitter design Williamson used is discussed in detail in the book, as is the method of designing a negative feedback loop encompassing the entire amplifier. Moers also gives a unique explanation of another pivotal power amplifier circuit: the ultralinear circuit invented in 1951 by Hafler and Keroes. It’s a case of content versus jargon.

In his otherwise excellent discussion of damping factor, Moers unfortunately makes the all-too-common error of ignoring the effects of voice coil  and lead wire resistance. He gives the common equation for damping factor: DF = (loudspeaker impedance)/(amplifier output impedance). Since the amplifier (modeled as an AC generator or Thevenin source), voice coil resistance, lead wire resistance, voice coil inductance, and reflected mechanical impedance form a series circuit whose actual damping is influenced by all elements, the lead wire resistance and voice coil resistance cannot be ignored. In fact, they can easily swamp the effects of the amplifier output impedance, at least for a pentode stage using negative feedback. However, Moers does not make the further error of insisting that the damping factor be a minimum of 100 as have some earlier authors. Using an 8-Ω speaker having about  6-Ω DC resistance, the effect of a combined output impedance and lead wire resistance less than 0.5 Ω is negligible.

Two shortcomings of Fundamental Amplifier Techniques with Electron Tubes are more or less linguistic. English may well be the only Germanic language in which the verb in a sentence is not at the end of the sentence required to come. Thus syntactical intrusions from the author’s native language sometimes make the text difficult for native English speakers. Also, Moers has chosen to use terminology that is probably not standard in English (at least American English) books on electronics. For example, he uses the term “ anode static steepness” to denote “transconductance” (also commonly called “mutual conductance.”) A common-cathode (or “grounded-cathode”) amplifier stage is called a “basic cathode” stage in Moers’ book.

These three small complaints pale in the face of the outstanding job the author has done in bringing together the theory, design, and practice of vacuum tube amplifiers in a single volume. Anyone who wants to go beyond the Heathkit level of tube amplifier understanding owes it to him/herself to buy and study this excellent volume.

If you’re interested purchasing the book or learning more about it, click here to visit the book’s webpage in the CC Webshop.

Fundamental Amplifier Techniques (by Rudolf Moers), audioXpress, and CircuitCellar.com are Elektor group publications.


Q&A: Per Lundahl (Transformer Design)

Per Lundahl is a multitalented designer who runs one of world’s leading high-performance audio transformer manufacturing outfits, Lundahl Transformers, which is based in Norrtalje, Sweden. After graduating from the School of Physics at the Royal Institute of Technology in Stockholm, he worked as a computer consultant for Ericsson. It wasn’t until he decided to move out of the city that he joined his family’s business, which his parents started in 1958.

Per Lundahl, CEO of Lundahl Transformers

In the April 2012 issue of audioXpress magazine, Lundahl shares stories about the company’s focus and products. He states:

I design all our new transformers. Our audio market is divided into two segments, Pro Audio and Audiophile. The Pro Audio segment includes transformers for microphones, mic pre-amps, splitters, distribution amplifiers, and other studio equipment. The Audiophile segment is transformers for MC phono cartridge step-up and for tube and solid state amplifiers.

Our biggest selling products are two types of transformers for microphone preamplifier inputs. In the Audiophile domain, our tube amplifier interstage and line output transformers are popular.

We constantly develop new transformers based on the requests of our customers. Presently we are developing an auto-transformer for a Chinese company and an interstage/line output transformer for some European customers. The latter will probably be added to our range of standard transformers, available to everyone.

For the very fastidious audiophile, we are also introducing silver wire in some of our transformer types. Initially, the wire will mainly be in our high-end MC transformers, but depending on the response, it is possible that we will extend the silver wire product range.

You can read the entire interview in audioXpressApril, which is currently available on newsstands.

Tube amp transformers

audioXpress is an Elektor group publication.

Raspberry Pi: Is It for You?

Unless you’ve been locked in your lab or design studio for the past several weeks, you’ve likely heard about Raspberry Pi, which is a compact, affordable computer that has been creating a buzz on the ‘Net for some time now. The group behind the computer is the Raspberry Pi Foundation, which is a UK-based charity that has an ever-growing following of more than 52,000 followers on Twitter!

(Source: TechTheFuture.com and The Raspberry Pi Foundation)

According to the Raspberry Pi Foundation, “The Raspberry Pi is a credit-card sized computer that plugs into your TV and a keyboard. It’s a capable little PC which can be used for many of the things that your desktop PC does, like spreadsheets, word-processing and games. It also plays high-definition video. We want to see it being used by kids all over the world to learn programming.”

The 85.60 mm × 53.98 mm × 17 mm Raspberry Pi weighs in at 45 g. It features a Broadcom BCM2835, including an ARM1176JZFS and a Videocore 4 GPU.

So, how can Circuit Cellar members use Raspberry Pi? Well, look at it in three ways. One, you can use it in a design of your own. Grab one and start building as soon as you can get your hands on one. Two, you can learn from the “story” of the Raspberry Pi Foundation—how it formed, how it works as a charity—and consider launching a tech foundation of your own. Three, you can design a low-cost embedded design platform or rapid prototyping solution—something distinguishable from the usual suspects of Arduino and mbed—and bring it to market.

In a recent post titled “What Are You Doing!?” at TechTheFuture.com, Tessel Renzenbrink detailed an interview with Eben Upton, a founder and trustee of the Raspberry Pi Foundation. Tessel writes:

Raspberry Pi is grabbing the attention with a $25 computer ($35 for a networked model). In the middle of the storm is Eben Upton. Why is he convinced that a computer which has no casing, no keyboard, no HD and no screen, will be successful? It is time to put the question to him: ‘what are you doing?’

‘We wanted to have a computer especially for Python, and there is a great tradition of naming computers after fruit: like Apricot, Acorn and even today there are computers named after fruit. So Raspberry is following the line of a rich tradition with the Pi, and yes, we wanted this connection with Python. That is where the Pi comes in’, explains Eben when asked for the name Raspberry Pi. And why is it a charity that brings this computer to the market? ‘That all has to do with value creation’, Eben continues. ‘I’ve been involved in several start-ups and then you always end up with the question; how will this create value?’. ‘In this case I do not have to worry about creating value. I can concentrate on designing and producing the board. The Raspberry Pi can be seen as a ‘white label’ product. If there are people out there with a commercial idea for this product, they are more then welcome’.

The Raspberry Pi is a bare PCB board; no keyboard, no HD, no screen.. how will this product become successful? ‘Basically, there is no reason why a computer has to cost more than $50. The peripherals like a screen and keyboard and storage will create a higher price, but with the Raspberry Pi we have taken another route – a normal TV can be used as a screen’, comments Eben. ‘Combine that with a ‘charity shop’ keyboard for a few dollars and you have a full working system’. He further emphazises that ‘the Raspberry is specifically aiming at youngsters learning to program’.

And how about the Raspberry Pi being ‘the next big thing’ after Arduino? There are many hints in that direction on the Internet? ‘The Raspberry Pi is different from the Arduino. The Arduino is great for direct applications and there are dozens of programs available. The Raspberry Pi is a computer system – designed to work with a screen and keyboard, a completely different idea. You can even watch videos with this thing. What might be interesting is the possibility to use the Raspberry Pi as a host for the Arduino board – the combination of these two, resulting in low priced systems can be very interesting and useful’.

‘There is also a difference the flexibility and usability, adds Eben. We have chosen for Broadcom chips and they are not easy to get in the market, making it very difficult to call the Raspberry Pi an ‘open source’ project. We are hoping to take this development into the open source direction, but that will require a new design’.

Can designers use the Raspberry Pi for different applications? ‘Yes, no problem. There is plenty of I/O (I2C and UART) to start using it for whatever challenges you’.

The first batch of 10,000 Pi’s has now arrived from the factory – what will be the next step? ‘Another 10,000 we hope and that is all just the start of it…’

You can read the entire post at TechTheFuture.com.

If you want to check out other kits and modules, visit the CC Webshop.

TechTheFuture.com is part of the Elektor group.