>>>READER-TO-READER QUESTIONS AND ANSWERS
a maximum wind speed to deactivate.
Also, it needs variable activate and
deactivate timers (about 30 seconds to
five minutes) so that wind gusts will
not activate/deactivate the circuit
There are several stand-alone wind
speed devices on the market, as well as
included in complete weather stations.
They all seem to be wireless in nature
and talk to some type of receiver
monitor or computer. A stand-alone
"wired" wind speed device to
controller circuit would be preferred.
#1 A stand-alone wired wind speed
alarm can be found at inspeed.com
under "windswitch." You can add an
external time delay relay like Ramsey
Electronics #K2579 (www.ramsey
kits.com) if the built-in delay is
#2 The easiest way to solve this is
probably with a hot-wire anemometer.
A mass flow sensor in a modern
vehicle uses the same principle. Linear
Technology ( www.linear.com) has an
application circuit for the LT1014
using a #328 bulb with the glass
envelope removed as a wind speed
sensor. A couple of comparators
connected to this circuit should give
you the desired result (look for
window comparator circuits and timer
circuits in the LM339 datasheet). You
can use Linear Technologies LTspice
IV to model the circuit.
[#7092 - July 2009]
We have been trying to find a
better way to keep track of thousands
of inventory items we have on campus.
We would like to do this the cheapest
and most effective way. Our budget
right now is not that large. We have
looked at a few applications from
i Tunes App store, but most of them are
web based — "Info already on the
web." I was wondering if RFID chips
could do this sort of thing? We want to
put the serial number, item name, and
model number into either a barcode or
80 November 2009
chip that can be stuck to the item. Is
the RFID system able to do this or very
inexpensive barcode software?
#1 RFID is practical and cost-effective. For the campus inventory
system, tags — which are about the
size of a postage stamp and about as
thick (there's a little bump where the
chip is located) — are available that
could store a few bytes up to 3,000
bytes for less than $1 each.
These tags can be written, read,
and re-written over the life of the asset.
The tags are "passive" meaning that
they have no internal power supply.
Portable reader/writers are available.
Tag data can be security protected.
I am personally working on a
prototype, portable reader which
should cost less than $100.
#2 A cheap and effective way to
keep track of your inventory would be
to label the inventory with barcodes.
You can do this for free by downloading a barcode font from the several
offered on the web. A search for
"barcode font free" will locate these.
Use any word processor with a label
printing function to generate the
inventory labels with your data, using
the special barcode font for the barcodes. You can read the barcodes
with a laser barcode scanner and
"keyboard wedge," which you can find
online by searching for "keyboard
wedge barcode scanner." A "keyboard
wedge" allows you to connect a
barcode scanner inline with your
keyboard. When a barcode is read,
the wedge inserts the characters read
into your inventory software, as if you
had manually typed the characters on
your keyboard. To use a keyboard
wedge with a portable computer, use
a "USB keyboard wedge scanner." You
may use any inventory software that
you wish, including free or shareware
programs offered online, as no
modifications need be made to the
inventory software to use a wedge
scanner. I looked at a few that might
work for you that are freeware on
ZDNet and download.com, simply
searching for "inventory software." The
website at www.taltech.com/products/
interface.htm has a good overview of
complete barcode reading systems.
Willow Creek, CA
[#7093 - July 2009]
Simple Low Frequency
How would I build a low frequency
(say 512 Hz), battery operated sine
wave transmitter that was small enough
to fit inside 1" PVC pipe? I'm not sure if
a resistor, capacitor, or crystal is the
best; how do you wind a coil antenna
to match the frequency?
I sell a programmable Quad DDS
chip that is very accurate in the audio
range (512.00 Hz) and four outputs. It
has a square wave output, but can
be converted to triangle, then filtered
A 555 timer chip and a few other
parts would be cheaper, but the freq
will drift with temp change.
As far as the antenna goes, at that
freq, just about any coil will work.
If you need a strong field, you can
drive the coil with a cheap audio amp
chip, like the LM386.
I can email you plans for most of
this stuff; SteveMerrell@Gmail.com
[#8097 - August 2009]
Need LCD Datasheets
I’m looking for datasheets or
advice on how to use an LCD unit
salvaged from a mid 1980's medical
device. The PCB is labeled "PWB641C-
CEM, OPTREX." There are 19 pins, two
of which are "A" and "K" which I
believe to be power for the backlight.
The chips are "HD44105H" and two
Anyone can type ANY CHIP ID
directly into any search engine and get
information from many sources.
The 'link' below will give you the
Saint Johnsville, NY