that repeats it 136 times to display the
complete message two times. The
scrolling does work, but sometimes it
starts at the beginning of the message
and other times it starts at the 41st
character. This action seems to be
random.
As I stated, I have tried inserting
several different commands just
before the scrolling routine but none
of them have worked. These
commands include repositioning the
cursor to position 128, the start of the
first line, homing the cursor ( 2), and
adding a cursor right and a cursor left
command after that. None of these
measures seems to have any effect.
Does anybody know of a reliable
way to have this scrolling message
always start at its beginning? If
possible, I need a solution that works
on all HD44780-based displays. I
know this is a tall task and may
need to use different approaches for
different displays.
#1153 Paul Alciatore
Beaumont, TX
[#12142 - December 2014]
Unregulated Power Supply
I picked up a 9V switching power
supply wart from one of the online
suppliers that advertise in Nuts & Volts.
Unfortunately, it melted two Arduinos
before I realized what was happening.
Apparently, the no-load voltage on a
switching supply can be up to twice
the rated voltage — in my case, 18V.
Should I add a load resistor to the
internal circuit of the wart so there's
always a load? Any other suggestions?
All you need is an appropriate
three-terminal voltage regulator to
protect your Arduino boards. I don't
know what voltage your board needs,
so I suggest integrating an LM317T
programmable regulator between the
board's power jack and the board. The
regulator will take the wall wart's
high voltage and reduce it to what
the board requires. To program the
regulator, connect it between the wall
wart and your board's DC input using
the Figure 2 diagram as a guide.
Wiring isn't too critical (
point-to-point), but keep lead lengths as
short as practical. Be sure to include
the two capacitors as they'll help
"keep things sta-ble" and prevent
unwanted high
frequency oscillations. NOTE:
The voltage
rating of C2
should be above
24V as it's
typically an electrolytic. Variable
resistor R2 will
let you dial in
the output to
what your board
requires. BE
AWARE: Keep
the maximum current draw BELOW
one amp; use a heatsink on the regulator (a TO-220 type clamp-on will be
sufficient) and keep the regulator's
input voltage below 35 VDC!
If you don't want to bother with a
variable resistor for R2, visit www.
reuk.co.uk/LM317-Voltage-Calcul
ator.htm as it has a nice table of
standard resistor values to use for
R1 and R2 for programming various
output voltages (and other good info
on the regulator).
Ken Simmons
Auburn, WA
[#12143 - December 2014]
Photomicrographs
I need photomicrographs of some
3D printed surfaces for a science fair
poster. Is there a commercial electron
microscope imaging service that you
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January 2015 79
Figure 2