the same time. Maybe switches
#1 To safely and efficiently use your
36 volt battery "pack" to run an inverter, you might consider a DC to DC
converter. "Solar Converters, Inc."
ers.com/ sells Model EQ 12/36-50
that puts out 12 volts regulated DC at
50 amps from a 36 volt DC input. Also
check out www.jameco.com Catalog
Part #217269CC which takes 19-36
volts DC input and puts out 12 volts
@ 12. 5 amps.
Bob Lindstrom, Broomfield, CO
#2 Yes, you can wire the six batteries in series-parallel to obtain 12
volts with lots of amps. You can
either parallel three sets of two batteries (in series) each, or else connect
in series two sets of three batteries
(in parallel) each.
Yes, you can use some form of
multipole switching to change from a
36V array (series) to a 12V one
What you will not be able to do is
to use the two voltages at the same
time: The switch will be in either the
“36V” position or in the “12V” one.
Also, to charge the batteries the
switch should be in one of the two
positions (according to the charger’s
voltage and current). To prevent accidents, you will have to add one pole
to your switch so that the charger
won’t be connected if the batteries
are in the “wrong” configuration.
And, of course, the switch should
be rated for the system’s voltage and
current. To open a DC circuit – even at
moderate voltages like 36V – is no
If you want to run your 36V loads
and an inverter simultaneously, you
should get an inverter that runs
on 36V. It will be not only easier to
connect, but it will use thinner wires
and be more efficient.
Buenos Aires, Argentina
[#1063 - January 2006]
I have a digital caliper. I would
like it to display measurements in
a third way besides inches and
millimeters. Are there digital calipers
that have generic microcontrollers
that could be reprogrammed or
replaced with my own programming?
If one of them has something like a
generic PIC in it, then maybe ...
Many digital calipers have a data
port hidden under a small cover. You
can interface the caliper to a desktop
computer using an appropriate cable
(ex. Mitutoyo Connecting Cable
#905409 www.mitutoyo.com) and a
converter box (ex. Smart Cable #200-
50R9F www.qualityonsale.com). This
can be an expensive proposition
given the cost of the cable is around
$40.00 and the cost of the converter
box is around $170.00. The good
news is that the converter box information comes with a sample Qbasic
program that illustrates how to read
the caliper value and display it on the
screen. Good luck.
[#1062 - January 2006]
I have searched for the Data
Sheet on TI's TMS9916NL chip. Any
help would be appreciated.
#1 The TMS9916 is from Texas
Instruments, and it's part of their
9900 series (circa 1978). The 9916 is a
Magnetic Bubble Memory controller.
The following link provides a
brief discussion on the part and its
Briefly, Bubble memory was the
first attempt to create RAM that
would retain its data after power was
removed; a sort of very early Flash
Ladera Ranch, CA
#2 I contacted TI tech support; they
were very helpful and found this 25
year old data sheet, which I have
posted at: http://us.share.geocities.
[#2061 - February 2006]
Last Fall, we put up a new
RadioShack long range VHF/UHF
VU-190 antenna and rotator.
There was an error in the parts
list of my answer (in the January
issue) to the Aquarium pump turn
off issue. The value of R1 should be
330K, not 3.3K.
The corrected parts list:
C1 1000 uF 25V
K1 Omron G6RN-1-DC12 (Mouser
Q1 2N6427 NPN Darlington
(Mouser P/N 512-2N6427)
S1 Push button momentary switch
Around April or May, I noticed
that the reception for the higher
numbered UHF channels seemed to
be getting worse. During Summer,
this problem seemed to worsen.
Thinking about it carefully now,
last Fall we got good to fair reception
on channels 36 and 29 and excellent
reception on channels 23, 19, and 17.
Now it has changed to fair reception
on channel 23 and passable on 17. All
the others are basically unusable.
Clearly, something has changed as
the temperature and weather are
similar now to when the antenna was
VHF reception has not changed
since installation and remains very
#1 You have a bad case of high
frequency loss. It is important that
you start methodically checking only
one suspected part at a time. Here
are possible trouble spots: You
might have a bad "F" connector at the
matching transformer, or the RTV
rubber has developed a hairline crack
around the coax connector or around
the twin lead pigtail on the transformer, letting in water. Silicone does
not stick very well to most plastics.
Also, with binoculars, look at the
connections at the antenna terminal
block and the antenna element insulators. Is there any debris such as
cobwebs, bird droppings, etc? How
old is the coax? If you used the old
stuff, dirt or corrosion at the "F"
March 2006 101