62 September 2017
READER - TO - READER TECHFORUM
What’s In A Board?
There are plenty of high quality,
double-sided printed prototyping
boards readily available on eBay. They
are perfect if used as they are, unless
— as it often happens — the need
arises to trim, grind, or otherwise
Here is my problem: I am deeply
concerned that these boards are
made with asbestos. I know that
for any grinding job a facial mask
is a must, but if the dust created in
the process could contain asbestos
particles, much stronger protection
measures would be warranted. Or,
perhaps such operations should be
I imagine that many electronics
enthusiasts cut or even grind these
items, completely unaware of the
danger they may pose. I tried to
gather information from the Web
about these products, with little
I would like to know — preferably
from an authoritative source — what
materials are used in production
of these (mostly Chinese in origin)
#9171 Jan Raj
Generators, Motors, and Other AC
I’m trying to make sense of
everything coiled, but the only thing
getting wound up is me! I thought I
knew a bit about electromagnetics,
but recently I’ve been trying to make
sense of all these fields and flows.
What is the difference between
the magnetic field and the flux? How
does flux work in a transformer or
a generator? Does anyone really
understand Maxwell’s Equations?
So many textbooks dealing with
electromagnetism speak in equations
instead of English. I want to know
HOW it all works, not just how to
compute these things. Am I just
reading the wrong books? Can you
help me figure out what the flux is
#9172 Taylor Street
My wife and I are hearing
impaired. We need an AVC amplifier
for TV audio to keep the level
constant going into Wi-Fi hearing aids.
Commercial or build-it-yourself (no
surface mount); analog not digital.
#9173 Fred Imm
Door Chime Protection Circuit
I need a way to protect my
hardwired door chimes from being
accidentally “burnt up” when the
doorbell button gets stuck.
A couple of times when the
button got stuck, I was home and
able to fix it before damage occurred.
The last time it happened, however,
nobody was home. Someone came to
the door, and we arrived home to the
smell of burnt electronics.
I’ve replaced the button more
times then I can count. I guess the
way the weather hits it — eventually
— it becomes stuck. I am now on my
third set of replacement chimes.
I have TWO 16 volt chimes
(10VA) wired to a single button (LED
lamp) on a 16V 30VA transformer.
The transformer is much larger than
normal to accommodate the two
I would like to protect the chimes
in one of two ways:
1) Simple protection — Inline fuse
that would blow if the chimes were
pulling current for more than (let's
say) five seconds. I figure a “
slow-blow” fuse would be ideal, but not
sure on the rating.
2) More complex protection — A
“time out” circuit that would cut
power to the chimes if the circuit was
live for more than five seconds, self-resetting either after the button was
released or after 60 seconds (chime
would activate again, indicating a
#9174 Eric Bailey
[#5174 - May 2017]
Do Good Kits Come From China?
I’ve seen extensive electronics
kits based on the Arduino and other
processors on Amazon for essentially
the cost of a bare Arduino. Are these
kits — presumably made in China —
any good, or is it a “You get what you
pay for” type situation?
#1 A lot of the products from
China are cheap clones; some are
of good quality and some are not. I
buy different type of modules for the
Arduino Uno to try. I am working on
a TEA5676 FM receiver.
I also support a lot of American
electronic parts stores in the USA.
I like Adafruit, as they have a lot of
tutorials on the products they sell.
This helps greatly with the learning
curve on the newer electronics.
#2 You asked an either/or
question. The answer is YES. There
are problems with many of these kits.
See question 1171 for an example.
They also usually have terrible or nonexistent documentation. However,
they do have the material in them to
support a great many projects and
demonstrations for an incredibly low
price. So, if you are on a tight budget,
they are well worth the problems.
Eagle Point, OR