-March 2009-
-An
Invitation to Circuit Cellar’s New Digital
Plus Venue
An
Invitation to Circuit Cellar’s New Digital
Plus Venue
Nearly a decade ago, Circuit Cellar Inc. was among the first
publishers to offer its magazines in digital format. The PDF downloads were
exact replicas of the print magazine and the system was immediately embraced by
those who wanted space-saving Circuit Cellar digital archives. In addition, it
became a real favorite for Circuit Cellar’s overseas readers who craved faster
delivery of Circuit Cellar content without premium subscription fees.
Today we’re giving everyone a sneak preview of Circuit
Cellar’s new digital delivery system. Welcome to Digital Plus… Circuit Cellar’s
expanded digital venue, which replaces our previous Electronic Edition system.
Those who have active Electronic Edition subscriptions will be rolled over to
Digital Plus automatically at no additional cost. Anyone not yet a subscriber
to Circuit Cellar’s digital delivery venue should consider subscribing as soon
as possible. While this sneak preview issue is open to the public, future
issues will be password protected for paying subscribers.
Why should you subscribe to Digital Plus if you already
subscribe to the print magazine?
·
Added features: Digital Plus can be read for approximately
90 days as an online flip book or as a PDF for your personal archives. No
special software downloads are required. The online flip book version will
contain additional video or photo slide-show presentations from our editorial
staff and advertisers.
·
More content: We call it Digital “Plus” because it
also includes bonus articles and content above and beyond that found in the
print magazine version.
·
More timely: One of the main reasons why authors
choose to have their material published in the Digital Plus bonus section is
the lead-time factor. By working outside of the limitations of print magazine
production schedule, Circuit Cellar content can be delivered to readers faster
than ever before. We expect this bonus section to expand considerably through
2009.
If you are a print magazine reader and would prefer not to
subscribe to Digital Plus, don’t worry. You will have an opportunity to view
the bonus sections of Digital Plus through a separate notification system at no
additional charge. Non-subscribers should simply watch upcoming News Notes
newsletters for availability announcements for the open-access bonus material.
Digital Plus subscribers will be sent a monthly availability
email from Circuit Cellar. In addition, Digital Plus subscribers can simply go
to http://www.circuitcellar.com/DP
and log on to any of the three currently available issues. Your previous
Electronic Edition email address and password serve as your new Digital Plus
login information.
A Note about the SR4
Many
readers inquired about the robot used in Circuit Cellar’s March 2009 Robotics
issue cover concept. The artistry of Circuit Cellar cover designer Chris
Rakoczy helped to capture the intrigue of the SR4 robot, which was provided by
the folks at Smart Robots (http://www.smartrobots.com/). Smart Robots describes the SR4 as “an over three foot tall, 50+ lb. payload
capacity mobile robot platform with Linux, wireless web connectivity, and
expandability (power connections, expansion/mount space and USB, Serial, I2C
and Wireless 80211.g and b connectivity). The SR4 is currently in use in North
and South America, the Pacific Rim and in Eastern and Western Europe as both an
educational tool and an application development platform.”
For those of you questioning the functionality of
the SR4 on a dirt path, well, let’s just say nobody had a problem with R2-D2
rolling around on the swamp planet Dagobah.
Are You In or Are You Out?
By Sean Donnelly,
Publisher—Circuit Cellar
Readers of
February’s News Notes saw me allude to a virtual punch clock at Circuit Cellar
headquarters. In reality it’s not so much a clock as it is an employee in/out
board. While some of the benefits of this system are easily duplicated today in
a variety of ways, this particular embedded solution still makes sense at
headquarters (where employees often find themselves away from their desks
working on a special project, getting lost on our archive floor, or helping out
at shipping/receiving with the latest sample shipment). The in-out board is so
easy to tag as the employee enters or leaves the building, it has become a
faster way for receptionists to figure out if they should try to track an
employee down inside the building or simply tell a caller the employee is not currently
at the office.
Details of this project first appeared in Circuit Cellar issue #137. Click here to download the article PDF for a quick blast from the past.
Build Your Own
Z80 Computer
Readers are encouraged to download this book of design
guidelines and application notes from Steve Ciarcia. Although the original
title first appeared in 1981, pre-dating Circuit Cellar “the magazine,” we
still get a number of requests each year from electronics enthusiasts. Some are
just interested in Steve’s brand of designing and ability to overcome
obstacles, while others still find themselves tweaking projects that use parts
described by Steve.
Please note: The original work was only available as a hard
copy. Thanks to Andrew Lynch and Bill Bradford for their work in creating the
PDF and getting permission to release it.
Scanning done by Bill Bradford.
“I am so very glad to see this wonderful BYOZ80C book made
available for all the home brew computer hobbyists. It really is a fundamental piece of any
computer hobbyist library and should be shared.
Steve's works have inspired me in many ways and I've been working on my
own home brew computer project (N8VEM).
This is a great hobby and I enjoy it very much. I am glad to see this book being published so
others can enjoy it too.” –Andrew Lynch
Two versions
have been uploaded as a courtesy to the larger design community.
For an
indexed version (web-based only), visit http://books.google.com/books?printsec=frontcover&id=mVQnFgWzX0AC#PPP1,M1
For a
version that can also be downloaded as a PDF, visit
http://www.scribd.com/doc/13388965/Build-Your-Own-Z80-Computer
EQ Interactive
CORRECTION: April 9, 2009
Typo reads (R2+R3)/(R2+R3). This typo crept into that line during the publishing process, and is not the fault of the contributor, David Tweed. If you change that term to (R2×R3)/(R2+R3), then the rest of the derivation is correct as it stands.
Problem—What is the load current ILOAD in the following circuit if
R3/R2 = R4/R1?
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.
Solution—This circuit is known as a “Howland current source.” The load
current is derived as follows. First, write down the equations for the voltages
at the inputs of the op-amp, using superposition to account for the various
voltage sources and the load current in the circuit:
Set them equal to each other and isolate the term containing ILOAD:
Note that if R3/R2 = R4/R1, the following expressions are also
equal:
This makes it easy to solve for ILOAD:
In other words, the circuit is a voltage-controlled current source. The
load current is essentially independent of load voltage. -EQ provided by David Tweed.
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