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for (a) what type of RFID chip to
use (there are more than one); and
(b) where I can obtain a bare-bones
scanner. I want to capture the tag ID
using my own microprocessor when a
cat is in range of the sensor.
RFID systems operate at different
frequencies. For the system to work
correctly, the frequency of the reader
must be tuned to the frequency of the
tag. The operation frequency of the
system made by Parallax may be
different from the frequency at which
the animal tag identification operates.
Even if both of them operate in the LF
range, one may be operating at 125
kHz and the other one at 134 kHz.
Moreover, even at the same operating
frequency, the communications protocol that they use may be different, as
these are not standard in the LF range.
You may want to experiment with
other low-cost readers for hobbyists. A
good source is here: www.trossenro
The popular website Instruct
ables.com has several projects related
to RFID systems (search for RFID).
From all of them, you may be interested in this one: www.instructables
Finally, there is a website that not
only describes in detail the chips used
by veterinarians, but it also gives
details to construct a reader. This may
be the closest to what you are looking
for. This website is www.maxmicro
[#4104 - April 2010]
I would like to put together a
flame sensor using flame rectification. I
am familiar with how it works however,
I need some ideas for the sensing
electronics. The furnace I have uses a
hot surface ignitor.
A simple flame rectification circuit
can be easily made with an
operational amplifier and a few
discreet components. Choosing the
popular '741 op-amp and one
megohm resistor for feedback, I was
able to breadboard a working circuit;
the output from the amplifier drove a
LED through a 330 ohm resistor. The
input from the sensing rod (wire, in
my case) went directly to the non-inverting (+) input of the op-amp; the
inverting input (-) fed back to the
output through the one meg resistor.
Powered with five volts, it readily
sensed the flame. In this case, I
"grounded" the test flame with another
wire. You can use this circuit to drive a
relay or input to your favorite
microcontroller. The very high input
impedance of the op-amp allows for
reliable low voltage operation.
Having said that, do not attempt
to alter or modify the existing ignition
and safety system in your gas furnace.
The hot surface igniter on the
domestic gas furnace works in
conjunction with a very clever infrared
flame detection system. It's designed
for safety and has to meet the
approval of various agencies before it
can be sold to the public.
Lemon Grove, CA
[#4109 - April 2010]
PIC Micro and USB
Long ago, I was competent
programming in Microsoft QBasic.
Now most/all articles use either
assembly or C. Do any of the popular
microcontrollers program in some
version of Basic? I am not into a "C"
level of retraining at age 67.
Suggestions ... I’m looking for serious
how-to articles — or worst case —
books on using some microcontroller
that includes interfaces to USB ports.
#1 I am an older techie like yourself
tinkering with microcontrollers. Like
you, I have used Basic for several years
and have not bothered to learn C or its
derivatives. Lucky for us, there are several well established companies that
build microcontrollers programmed in
Basic. Parallax ( www.parallax.com)
sells the BASIC Stamp that is available
in several versions, depending on
features you need and how much you
are willing to spend. The unit comes in
a 24-pin DIP package that you will
need to mount on a perf or breadboard to ease interfacing to. You can
also purchase a complete development board with USB interface. Basic
Micro ( www.basicmicro.com) offers
the Basic Atom which is also available
in several versions. Both companies
offer free downloads of an Integrated
Development Environment (IDE) that
allows editing, debugging, and
compiling of programs on a PC or
Mac. I have used both successfully in
several projects. If your preference is
the PIC line of microcontrollers from
Microchip, microEngineering Labs
( www.melabs.com) offers a complete
line of Basic development systems
for this product line. All of these
companies have tutorials you can
download or literature you can
purchase to assist you in learning how
to use their products. There is also
a wealth of third-party information
available and forums you can enter to
assist you. P.S. I recently purchased an
Arduino which is programmed with a
language that is a subset of C in the
hopes of disproving the theory that
you can't teach an old dog new tricks!
#2 I've been using the mikroBasic
software from mikroElektronika (www.
mikroe.com) for years now and am
extremely satisfied. Good news is that
you don't even have to buy the
software if your projects can compile
under 2K of code space. This is more
than sufficient for all beginner level
projects. I think they probably make
most of their profit selling their
September 2010 79