display will show. However, it should
work lower, with some caveats. Your
question does bring up a very
important point that needs to be
The ratings listed in datasheets
are those that the component was
designed for and tested to. If a part
fails prior to reaching its maximum
rating, then it is defective and —
depending on return policies —
should be replaced.
Fortunately, many components
don't fail abruptly. They tend to
deviate from their normal function.
So, I expect my thermometer will
need an adjustment to its calculated
temperature as its gets colder. This
can be done with software, so it's
trivial to fix.
My flight computers and sensors
produce output that changes
gradually during a flight. Since I don't
see an abrupt change in sensor
output, I know there's no significant
failure. There may still be calibration
issues to deal with, but I expect
Power to the USB
Thanks for the January 2015
PICAXE Primer column, even though
I don't use PICAXE. It was an
interesting look at USB that I've not
looked into before. Out of curiosity,
is there not a need to include any
filtering caps on the supply? I'm sure
that the supply from a PC is relatively
clean, but what about the wall wart?
I'm glad you found the January
Primer article interesting, Andrew!
Your email prompted me to pull
out my scope and run three separate
tests. I connected a USB cable to the
following three voltage sources, and
took a look at the +5V power line in
1. A USB port on my PC.
2. A powered USB hub.
3. A 5V (1A) USB wall wart.
To place a load on the supply, I
connected a 1K resistor between +V
and ground on the breadboard. As
expected, the output voltage did vary
slightly among the three power
sources (from 5.2V to 5.4V), but
otherwise, all three sources produced
essentially the same result: There was
a small high frequency ripple (about
18 mA 20 MHz).
I have been using an FTDI USB-to-serial cable for powering and
READER FEEDBACK Continued from page 7
The College of New Jersey, Ewing, NJ
Saturday, March 21, 2015
9:00 am –– 5:00 pm
Registration/Flea Market open at 9 am, Talks start at 10: 15 am.
• Android Wear talk by author Barry Burd
• Project Tango • Android/iPhone Apps
• Raspberry Pi Tutorial and Projects
Admission: $10.00 (advance)
$12.00 at Gate
The 2015 Trenton Computer Festival TM is sponsored by The College of New Jersey and its School of Engineering.
THE ORIGINAL PERSONAL COMPUTER SHO W
The College of Ne w Jersey Hosts
The 40th Anniversary of TCFTM 40 TCF TM 40
INDOOR FLEA MARKET & VENDOR FAIR
50+ Talks, Workshops, Tutorials,
Demos and Special Events!
Object-Oriented Programming University:
One Day of Short Courses by Mike Redlich
Microsoft Presentations and Special
Workshop on “Safe Computing”
Quadcopter and 3D Printer Demos
Tour the Sarnoff Museum of Tech.
MULTIMEDIA, SECURI T Y,
PHOTOGRAPH Y, HOME CON TROL,
HISTORIC COMPUTERS and WIFI
Ham Cram Session & Exam:
Get an Amateur Radio License in
one day at TCF! Cram begins at 9 am
Arduino Developer/User Tutorial/
of the 40th TCF!
Wearable Tech Insider,
IEEE/ACM I T PROFESSIONAL CONFERENCE
Friday March 20, 2015, 8: 30 am — 5:00pm**
Continuing as part of TCF’s Saturday Talks.
For Conference Info and Fees See
For additional TCF’ 15 info,
directions and advance tickets:
**The I T Pro (Friday) and ISEC Conferences require separate registrations.
IEEE Integrated STEM Education Conference (ISEC)**
Saturday, March 7 – 8:00 am — 5:00 pm
at Friend Center, Princeton University, NJ
Creating a Culture of Achievement
March 2015 45
Continued on page 81