-November 2009-
-iMCUW7100: Embedded
Networking Made Simple
iMCUW7100: Embedded Networking Made Simple
The WIZnet iMCU Design
Contest is well underway. Be sure you read Dave Tweed’s contest primer article iMCUW7100: Embedded Networking Made Simple.
In the article, Dave describes how the hardware TCP/IP stack of the W5100 has been
enhanced in the W7100 with the addition of an on-chip 8051 application
processor core, eliminating the need for a separate processor chip in many
applications. He provides an introduction to the new chip and an evaluation
module that’s based on it. Read it now!
Note from the publisher:
As you may already
know, unlike with previous Circuit Cellar design contests, there isn’t a large
supply of free evaluation boards associated with the iMCU Design Contest.
Boards that contain the W7100 device are available at a discounted price at FutureElectronics.com for a limited time. That said, I have been
able to set aside 15 iMCU7100EVBs for those with demonstrated capabilities who
really wish to participate in the design contest.
Normally, I wouldn’t use
a large venue like News Notes to talk about samples in quantities so small.
Certainly, your chances of receiving the free kit are small and depend on how
many others make similar requests and provide detailed information about their
background, capabilities, and contest intentions. Basically, complete the form,
but please keep in mind that only a few will be able to receive the free kit.
To be fair to you, note that I will personally notify you via e-mail within one
week if your sample request has been approved or denied.
To make your request, click here and complete the
request form.
Sincerely,
Sean Donnelly, Publisher
EQ Interactive
Problem—A 4- to 20-mA sensor used in
an industrial process needs to have galvanic isolation between its current loop
and both the power source and the equipment reading the sensor. The following
circuit is proposed as a solution. A 1-kHz square wave oscillator feeds a
MOSFET H-Bridge that is used to drive the primary of a small audio transformer.
A resistor at the bottom of the H-Bridge samples the synchronously rectified
primary current of the transformer. The secondary of the transformer is
full-wave rectified and filtered to drive the isolated current loop.
.
What
are some of the potential problems with this design?
Think You Have a
Great EQ Challenge of Your Own?
E-mail your best EQ question and answer to eq@circuitcellar.com
for a chance to be recognized by Circuit Cellar as an EQ guru.
Answer—The
design works by creating an isolated DC-DC converter to drive the sensor, and
measuring the current on the primary side of the isolation transformer, which
should be proportional to the sensor current. The square wave drive minimizes
the ripple current in the capacitor on the secondary side, so it should be
insignificant relative to the DC current of the sensor. In any case, it should be
a constant offset. There will be some losses in the transformer itself. The
magnetizing current will cause a fixed offset, and the resistive losses in the
coils and the core will require a scaling factor.
Author Q&A: Miguel Sanchez
Editor’s
note: Miguel Sanchez holds a B.S., an M.S., and a PhD in Computer Science. He
has taught computer networking courses at the Universidad Politécnica de
Valencia, Spain, since 1989. Circuit Cellar has published four of Miguel’s articles: (i) “Build a Digital Video
Recorder,” Issue 174, 2005; (ii) “Beam Up That Serial Port: Send
Serial Communications Via the ’Net,” Issue
193, 2006; (iii) “Reverse-Engineered ECP Bus,” Issue 201, 2007;
and (iv) “Vertical Plotter System,” Issue
212, 2008. His fifth article, “Three-Axis Stepper Controller,” is scheduled
to appear in a 2010 issue of Circuit Cellar.
CIRCUIT
CELLAR:
Many of our readers are familiar with your work, but don’t know much about you.
Where do you live and work?
MIGUEL: I live in
Valencia, Spain. It’s a lovely city by the Mediterranean Sea with mild winters
and hot summers. I’m been a tenured associate professor at Universidad Politécnica
de Valencia since 1992. I’ve been teaching about computer networks for the last
20 years.
CIRCUIT
CELLAR:
You have BS, MS, and PhD degrees in Computer Science. Does most of your
consulting work these days focus on IT and programming projects, or do you do
work on MCU-based projects and embedded programming apps?
MIGUEL: I’m a
systems guy. I like projects that have a direct interaction with the physical
world. My latest consulting work was around embedded systems for the
solar energy industry. ARM-powered embedded computers running µClinux have been
used. I try not to get involved in big IT projects, but often I’m asked to
interact with existing server platforms.
When I was a teenager the kind of development
I did was for isolated systems. Nowadays everything is connected. You need to
know how to chat using any possible protocol, and monitoring tasks can be much
tighter and ubiquitous. People love to check the performance of their solar
farm from the pool.
CIRCUIT
CELLAR: How
long have you been following Steve Ciarcia and reading Circuit Cellar?
MIGUEL: I started
reading borrowed copies of Byte magazine in the early 1980s. I was a teenager
then. I was going to a computer shop in my city that allowed me to use their
computers. The Apple II was the most used home computer at that moment, but
there was no way I could afford one. Going there I could use it for free and I
could read some computer magazines. Byte magazine was one of them.
At that time, I was mostly interested in
electronics, and all that combined experience sparked my career in computer
science. A few years later, I decided to study computer science, but I’ve
always kept my solder at hand.
I’ve been reading Circuit Cellar from day one, though I might have missed some
of the early issues. I was aware of the new path Steve was following after he
left Byte, and I’ve always enjoying reading his column. I’ve learned a lot
reading Circuit Cellar and Steve’s columns, and I still do.
CIRCUIT
CELLAR:
How long have you been designing MCU-based systems?
MIGUEL: I’ve never
been a professional designer in the real sense, as I’ve been working as a
university lecturer for a long time. But I’ve been designing MCU-powered
systems since I got my first computer in 1979. In case you're wondering, it was
an Ohio Scientific Superboard II http://oldcomputers.net/osi-600.html).
I knew other people had built systems around Motorola’s 6800, but I was looking
for something I could program using BASIC and that was kind of affordable. And
by the way, that was Microsoft BASIC Interpreter.
CIRCUIT
CELLAR:
What was your first MCU-based design, and why did you build it?
MIGUEL: My first MCU-based design
was a clone of Intel’s SDK-85. We were using these boards at the university
labs. I was not very happy having to program things using a hexadecimal
keyboard and display. Boards were not very reliable, and I realized that Intel
firmware included a serial terminal on the monitor software. I built my
own board, but without any keyboard or display, just a serial communication. I
interfaced it to a computer running CP/M. I used CP/M assembler to write my
programs, and then I dumped the binary code to my board to run the lab’s
exercises. It worked great, and I got an “A” grade on the subject. Using a
timer to the WAIT signal, I created a dumb EPROM programmer in the same system.
I just needed to dump the data content I wanted to write and have my own home
programmer.
CIRCUIT
CELLAR:
We published your first Circuit Cellar article titled “Build a Digital Video
Recorder” in 2005. Tell us about that project. Why did you design the system?
Do you still use it today?
MIGUEL: At that
time, digital video recorders were not available in Spain. The systems started
to appear in the USA (e.g., TiVo) and it just seemed right. Hard drives started
to have large capacities to hold tens of hours of video. Even more, some
satellite providers just switched to the use of digital video broadcasting
(DVB), as it was a more bandwidth-efficient way of broadcasting TV channels.
DVB computer boards were available too, so it was just a question of
putting everything together.
Merit, however, is not always given to the right person, so I would like to set
the record straight: The software I used was written by the German programmer
Klaus Schmidinger. He in turn was using Linux video interface to make his
VDR software possible. I think he did a brilliant job of getting a stable
system with a good user interface. All I did was to put everything together.
What has changed over the years is that broadcasters have been updating their
conditional access systems (i.e., DRM). While this was not a problem for
regular subscribers that use the broadcaster-provided receiver, it was at times
a show-stopper for those receiving the signal and doing the processing on a
different hardware.
Eventually, I discontinued the use of the system, but not because it was not
working OK—but because I switched to a cable TV provider. Now I miss some of
the features I had in the past with my old digital video recorder. Unfortunately,
my cable TV provider does not offer a DVR-enabled decoder.
CIRCUIT
CELLAR:
Two of your most recent projects are a vertical plotter system and the
three-axis stepper controller. Is motor control your main area of interest
right now?
MIGUEL: Not really.
As I’ve said, I like to build things that have a practical use. In that sense,
motors may help you to act in the real world. But my work on these two projects
has been fairly limited from a motor control point of view. I know that
electrical engineers have a much deeper understanding of electric motors.
The reason for some of my articles has been my willingness to share my findings
with others. I’m not trying to impress anyone. I just want to show how things
can be achieved, sometimes with more ingenuity than boring details.
And, once again, I would like to mention that the vertical plotter idea, while
a very fun project, was not my own idea. I saw a similar design on the
Internet. Again, there was a practical need behind the project: I wanted to help
my wife get several canvases painted with the same charcoal outline for a
personal project. The three-axis steeper controller project came from the need
of getting a multi-platform solution for the vertical plotter.
CIRCUIT
CELLAR:
We’re publishing your article “Three-Axis Stepper Controller” in early 2010.
Why did you decide to build a
platform-independent driver board rather than just purchase one on the
Internet?
MIGUEL: Sometimes
you find things that are great. I was amazed when I learned about the Dallas
Semiconductor DS5000 MCU. It was an 8051 MCU with battery-backed RAM that could
be programmed using a serial interface. For me, that was a nice discovery
because it made the development process much faster, convenient, and cheaper.
I experience a similar level of
excitement when I learned about the Arduino platform. I recognized the
huge potential it had, so I started using it for some pet projects (i.e., a
mood lamp based on an Arduino and a 3-W RGB LED).
Because the Arduino platform delivers a
simple way to connect the MCU to a USB port, I thought it was a good way to
break my dependency on a Windows host for the vertical plotter project. There
was nothing wrong with the other USB stepper motor driver, but it was fun to
create a new one. Besides, I figured other people might benefit from having a
three-axis stepper motor driver for the Arduino platform.
CIRCUIT
CELLAR:
Would you use it again?
MIGUEL: Arduino allows me to relax.
I do not have to dig into the MCU datasheet to figure things out. Several
simple libraries and a simple multi-platform development environment are
provided. I can concentrate on writing a small program. I then click a button
and it’s compiled, uploaded to the target, and then run.
All of it is powered via the USB port on my computer, so I don’t even need an
external power supply. Or course, you will need an external power supply for an
autonomous system, or when you need to draw more current than what’s available
via the USB port (more than 500 mA).
I will definitely use it again. But I’m not always looking for super-high
performance. If you want that, there are special integrated circuits from
companies like Allegro. Those can do micro-stepping with current-sensing and
use high-voltage power supplies.
CIRCUIT
CELLAR:
Do you have any advice for Circuit Cellar readers who are considering building
their own platform-independent driver board?
MIGUEL: Yes, I
think that the more you know about the process, the more freedom you have to
make changes. While there are great commercial boards that can do the job, the
feeling of achievement you get when you accomplish something on your own is
worth it. But, if you are wearing your engineer hat and you’re on a tight
deadline, an off-the-shelf controller may be a better fit. You’ll need a decent
budget though.
CIRCUIT
CELLAR:
What projects are you planning for the near future?
MIGUEL: One of my
students has developed a multi-hop wireless sensor network based on micro
Arduino boards and XBee wireless modules. We are planning to use that platform
for environmental monitoring in campus buildings.
When I was living in Berkeley during California power crisis, I met a group at UC Berkeley that was trying to develop
control strategies to ease the demand on power grid. Even today, I still think
we can make better use energy if we are able to monitor energy consumption.
Right at this moment, I have a window open because I am trying to cool down my
office. The room temperature is 81°F, which I
feel it is too warm. As I do this, the heating plant is heating up the
building. This sort of situation reminds me that we all can definitely do
better in terms of our energy usage patterns.
NEW PRODUCT ADVERTISEMENTS
ETRX3 ZigBee Module
Available From Lemos International
The ETRX3 series is the 3rd
generation of advanced ZigBee modules from Lemos/Telegesis and the first
module family on the market to feature the EM357 and EM351- the latest ARM®
Cortex M-3 SOC's from Ember.
ETRX3 series modules have a footprint of just 19mm x 25mm for both standard and
PA/LNA versions which represents a 40%reduction in size compared to the ETRX2
module. They will be available with either an on board antennae or a Hirose
U.FL connector to allow connection of external antennae.
A link budget of 105dB on the
standard ETRX3 module gives excellent performance and RF power can be further
boosted by use of the ETRX3-LR which adds an extra LNA+PA boosting the link
budget to 123dB.
The ETRX3 series are low
power 2.4GHz ZigBee modules integrating a 2.4 GHz, IEEE 802.15.4 compliant
transceiver with up to 192k of flash, 12k of RAM, and many advanced
peripherals.
The EM357 and EM351 utilize
an efficient architecture that exceeds the dynamic range requirements imposed
by the IEEE 802.15.4-2003 standard by over 15 dB. The integrated receive
channel filtering allows for robust co-existence with other communication
standards in the 2.4 GHz spectrum, such as IEEE 802.11 and Bluetooth.
The ARM® Cortex M3
microprocessor is optimized for high performance, low power consumption, and
efficient memory utilization making it ideal for use in ZigBee applications. To
maintain the strict timing requirements imposed by the ZigBee and IEEE
802.15.4-2003 standards, the EM357and EM351 integrate a number of MAC functions
into the hardware handling automatic ACK transmission and reception, automatic
backoff delay, and clear channel assessment for transmission, as well as
automatic filtering of received packets.
ETRX3 series modules work
from a 2.1v to 3.6v supply and active power consumption is reduced by over 20%
compared to the ETRX2. In deep sleep mode, current consumption is reduced to
800nA and further reduced to 400na if the self wakeup feature is not enabled.
ETRX3 series modules features
all the advanced software already present on other Lemos/Telegesis ZigBee
modules such as the Lemos/Telegesis AT command set which allows the
designer to use the functionality of the EmberZNet stack without the need for
complex embedded code. Development is also made easier by the addition of an
integrated JTAG and debugging interface.
As with all our modules,
ETRX3 series devices are designed to be easily integrated into designs without
the need for RF or embedded expertise. Using the latest version of Embers Znet
PRO meshing technology ETRX3 family modules allows designers to add the latest
meshing radio technology without complex software engineering.
For more information contact:
Lemos
International Co. Inc.
1275
Post Road Suite A-12
Fairfield
CT, 06824
Tel: 866-345-3667
Fax:
203-254-7442
PoScope Mega1 is World’s
First Low-cost PC-based Mixed Signal Oscilloscope,
Which Provides the
Features of Many Benchtop Instruments in One USB-powered
Compact Box.
PoScope
mega1 is world’s first low-cost PC-based 12 bit mixed signal oscilloscope,
which provides the features of many benchtop instruments in one USB-powered
compact box: 2-channel scope, 2-channel spectrum-analyzer, 2-channel
chart-recorder, 8 or 16 channel logic-analyzer and an 8-channel patternPWM or
square signal generator. Additional 5 analog channels will be supported with
software upgrade, so 7 analog channels will be available in total.
The
Oscilloscope capability provides a 2-channel 12-bit -20V-to-+20V 100S/s to
1MS/s mixed signal oscilloscope, with marker measurements, triggering
(absolute, differential, pre-trigger, external), math functions and signal
voltage and frequency measurement, and filtering. With 12k bytes sample data
buffer in buffer mode and virtually unlimited buffer in pipe mode you can view plenty
of information.
The
2-channel Spectrum Analyzer feature offers marker measurements, distortion
measurement, and various filtering options.
The Chart
Recorder can record and display signals from 0.01S/s to 1MS/s for virtually
unlimited recording time with marker measurements, the ability to add comments,
max/minimum/ average voltage measurement for each channel, etc.
The Logic
Analyzer offers a useful 16-channel, 1kHz to 10MHz
recording, with 8-channels still available if the internal 8-channel pattern
generator is on. Marker measurements are provided, as well as several
triggering options (edge, level, mask, pre-trigger, external clocking, preset
missing pulse, preset bit sequence/edge, etc.)
Remarkably
in an instrument at this low cost, it includes free handy visual decoding of
UART, SPI, I2C and 1-Wire interfaces.
Additionally,
the USB interface allows you to record, output, import,
export and print all waveforms or even update the firmware as new
features become available.
PoScope
software version 4 sets new standards on oscilloscope software. With its multi
window capability it supports also connecting of more PoScope devices on the
same time. As first and only it adds mixed signals capability to low cost
oscilloscopes.
In 2010 a
free software development kit will be published which will allows users to
write
custom visualization plugins.
PoScope is
available now from stock from PoLabs at www.poscope.com
