-JULY
2009-
-More
from Ciarcia’s Circuit Cellar
-CAN Prime: Creating
Your Own Network
-Understanding Antenna Specifications and
Operation
-Choosing Your Next
Value-Priced Oscilloscope
-Need help adding a graphical color control to your
product?
-Critter Chronicles – The War Continues
-Circuit Cellar’s Developer’s Marketplace
EQ Interactive
Problem 1—The following circuit was recommended as a preamp for
a speaker being used as a microphone in an intercom system.
What is the configuration of
the first transistor called?
Problem 2—What are the
advantages of using this circuit configuration for this application?
Problem 3—What are the other
disadvantages of this circuit?
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 1—The
configuration is known as a common-base amplifier. The input signal is applied
to the emitter, and the output is taken from the collector of the transistor.
Answer 2—The
common-base configuration provides unity-current gain in addition to a large
amount of voltage gain. Because the speaker is a low-impedance source, it
operates at relatively high currents and low voltages. This arrangement of the
transistor acts to impose the AC current of the speaker across the much larger
load resistor connected to the collector, providing voltage gain equal to the
ratio of the impedances.
Answer 3—The
biggest problem with this circuit is the fact that the impedance of the speaker
varies quite a bit with frequency, which makes the voltage gain of the circuit
vary as well. The low-value emitter resistor helps to limit this effect.
More from Ciarcia’s Circuit Cellar
As promised, here are a few more books in Steve Ciarcia’s
Circuit Cellar series. The following books were published in ’86 and ’88, just
before Circuit Cellar “the magazine” was launched.
Ciarcia’s
Circuit Cellar, Vol. 5
Ciarcia’s
Circuit Cellar Volume V documents 15 more projects in the continuing evolution
of my practical approach to high-performance computing. The projects in this
volume fall primarily into categories of “control” and “real world I/O.”
Scattered among them are tutorials on subjects as varied as the intricacies of
the telephone system, moving display sign technology, and the effects of radio
frequency interference.
Ciarcia’s
Circuit Cellar, Vol. 6
Circuit
Cellar Volume VI contains some very significant projects, including a complete
home control system, a high-performance single board computer system, and the
essential ingredients for a data acquisition and control system. They might
further be described as my favorite project, the readers’ favorite project,
and one of my most successful projects.
Featured White Papers
CAN Prime: Creating
Your Own Network
CAN
is extensively used in automobiles and trucks but has found applications
everywhere. There are many “application” layers available for CAN such as ISO
15765 (cars), J1939 (trucks) and CANopen (factory automation) but it is very
easy to develop your own protocol that will fit and simplify your needs. Modern
CAN transceivers provide a stable and reliable CAN physical environment without
the need for expensive coaxial cables. Most of the mystery of CAN has
dissipated overthe years. There is plenty of example CAN software available to
help you quickly develop your own network.
Understanding Antenna
Specifications and Operation
Since voluminous texts have been
written about each of the many antenna styles, it is unnecessary to cover them
all here. This article will focus only on those styles which are commonly used
in low-power handheld products: dipole and monopole whips. These styles cover a
wide range of available antennas, and are among the most common to be
implemented incorrectly. With that in mind, there are several rules-of-thumb
that can be applied to antenna designs. These rules are less “how to design an
antenna” and more “how to design with an antenna.”
Choosing Your Next
Value-Priced Oscilloscope
Digital oscilloscopes have come down
in price amazingly over the past few years, but can you get a good scope for
around $1,000? Do you really need some of the more advanced scope features like
math calculations or deep memory depth? Single-shot, delayed sweep, pre-trigger
acquisition, parametric measurements, saving waveforms and data for later
analysis, noise reduction, averaging, searching, zooms, and math measurements
give you helpful troubleshooting and analysis tools but these can be extras you
may not need.
Need help adding a graphical color control to your
product?
“LCD controller technology is new to me. Where do I
start?” That question is common nowadays. Most
manufacturing companies are seeing the value – maybe the necessity – of color
touch control technology. Many of them don’t have a long term or close
association with the technology, yet they expect their embedded engineers to
handle the project successfully and on a tight schedule. These engineers oft en
have questions...
Critter Chronicles – The War Continues
Note:
An update on Priority Interrupt #228
I swear that these moles are
out to get me. They have even started digging tunnels between the edge of the
garage and the blacktop driveway. The good news is that this very irritating
dig-site afforded a perfect place to retest the method typically suggested by
commercial exterminators – castor oil. I tried spreading castor oil a year ago
and I didn’t see any difference in the mole population so I wondered if I had
used enough oil. For this test I bought
a quart of MoleMax (castor oil mixed with a dispersal solution). Rather than
attach it to a hose and treat 10,000 square feet as the bottle suggested, I
poured the entire bottle along the 20 foot strip of soil between the concrete
and blacktop where the mole keeps digging. After soaking it in with about 25
gallons of water I thought that surely, an entire bottle would have some affect.
About a week after the
concentrated application of castor oil, I snapped this picture. Apparently my moles don’t care!
If you can’t beat ‘em, crush
‘em. Seriously, The biggest aggravation about moles is the ugly raised tunnels
across the flat mulch. I had already determined that lots of vibration (from my
big tractor) kept them away for a day or two but the big agricultural tread
tires tears up the yard more than the moles. But just any vibration doesn’t
work either. The experiment with the buried motor vibrators was a dismal
failure. The only way to still get big
vibration was to use my smaller tractor (with turf tires). I added a 625 lb
(water filled) lawn roller that flattens all the mole hills too. While the jury
is out on its ultimate success, there is a great deal of satisfaction that
comes from squashing the little suckers as I even out their dirty work.
Built, but untested as of
yet, desperation breeds invention. One of the mole abatement methods frequently
mentioned on the Internet is pumping Carbon Monoxide into the mole tunnels.
Certainly, attaching a hose to my pickup truck might guarantee substantial CO
but there is no way I can get the truck out in the back yard without doing more
cosmetic damage than I’m trying to prevent.
Fortunately, all of us who
live in the woods have lots of gas powered devices. Disregarding chain saws and
handheld gas-powered devices, the most portable exhaust generator I have
appeared to be either my 2-cycle 3 HP (30 lb) snow blower or my 4-cycle
10 HP (very very heavy) snow blower. I decided to try simple and light first.
The picture shows the
result. Rather than attach the hose directly to a hot exhaust pipe, I added a
6-foot piece of galvanized pipe to cool the exhaust before it enters the hose.
Still, the exhaust is too hot to touch so I used a high temperature rubber hose
(and hope it all doesn’t melt).
Finally, yes, I know that
this 2-cycle engine is very inefficient for producing CO. Given the back
pressure added by the hose, the exhaust is probably mostly unburned
hydrocarbons. Of course, I hope all that crap is just as breathable as CO. If
this combination is a bust, I just move the apparatus to one of my many other
4-cycle engines and gas ‘em again ;-)
Note:
For a look at what a few readers suggested to Steve as an alternative, check
out the Rodenator movies at that company’s web site http://www.rodenator.com/
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