launch platform (to reduce the IR
losses in the cable).
During use, a MOSFET failed and
a student was almost hurt when the
rocket launched prematurely. I had
failed to consider the consequences
of all possible component failures. I
added more safety features, but I
learned a couple of lessons about
“keeping it simple.”
In the April 2017 Q&A column,
Kristen McIntyre mentioned a circuit
using a 555.
I'd like to point readers to my
web page that shows a calculator for
monostable and astable. I also have
created a file that I add to often. It is
a monostable chart with various
frequencies and duty cycles.
My home page is at http://elec
urls.tripod.com/, but this is a link to
get to the matter at hand: http://elec
As a faithful reader, I’m sure
someone will find my chart useful.
Crescent City, CA
More Power to You
A friend gave me his used copy
of the July 2015 Nuts & Volts.
I found Eric Bogatin’s article on
power supplies very interesting. I
have a bunch of those wall warts
(who doesn’t) and use them with
varying results. Bogatin’s explanation
and suggestions are most useful.
I am a rather new Arduino
enthusiast and enjoyed teaching the
basics at our local middle school this
RE: Bryan Bergeron’s editorial on
heirloom build quality in our projects.
My husband (Greg W2ORO) recently
completed his dream variable bench
power supply. From the get-go,
quality was a priority, and he fully
expects this piece of equipment to
outlive him. Inside, there is a
Hammond plastic enclosure labeled
"Spare Parts Bin" which contains an
extra pilot light bulb, fuses,
transistors, and ICs. He even used
sockets on the four TO- 3 transistors.
We strongly agree with you on good
documentation. In addition to the
schematic, he created a two-page
circuit description, a detailed parts
list, and three pages of calibration
instructions. He really wanted to
place the paperwork inside the
enclosure, but the only panel of the
aluminum enclosure without
components mounted on it is the
top. Even the bottom is littered with
screws, preventing an adhesive
envelope on the outside. As for the
top panel, he was concerned that the
numerous pages inside the hot 15
amp power supply would be a fire
hazard. Would you worry about
Also, we’d like to know more
about using a "plastic pouch" to
contain the paperwork inside the
cabinet. Are there self-adhesive
pouches made for use inside
electronics? Or, what about just using
a zip-lock bag?
And, yes, he installed bolt-on feet
on his power supply!
Judy May W1ORO
Nice project! I wouldn't worry
Regarding the plastic pouches:
I've had good luck with the envelopes
from UPS/FEDEx designed to hold the
Old School is Best
Thumbs up on Bryant Julstrom's
article: An Old-School Digital Clock!
Keep up the old school doctrine!
Fundamentals are far more important
than shiny black boxed appliance
projects. (If this is an April Fool's joke,
it would be mean. Ed. note: It’s not a
joke.) Kudos to him for selecting
commonly available components
with the exception of the TN3109.
(Nobody's perfect.) I think he should
have used garden variety 2N3904s or
2N2222s. These will be available into
the "next millenium."
Also, super job on using seven-segment LEDs. One cannot go wrong
with seven-segment LEDs. Using an
LCD would have tainted the project.
Appreciate the feedback from a
fellow old school guy.
May 2017 7