means no voltage out and the device
is protected, but you’d better make
sure the power supply is fuse-protected
because the input is now grounded!
That said, here’s a pinout chart of
the most popular three-pin regulators
(Figure 3). On purpose, I didn’t
include a prefix — such as LM —
unless necessary. That’s because a
78L05 can be labeled as KA78L05,
L78L05, MC78L05, etc. Although the
electrical ratings may vary from
vendor to vendor, the pinout is always
the same. (A PDF version of
this chart can be downloaded from
our website, www.nutsvolts.
com under the name PINOUTS_
Vreg.PDF. — Editor Dan.)
100k 8 4
Solar Burglar Alarm
Q. I am in need of an alarm for a
new storage building where I do
not have utility power. Instead, I want
to power the alarm from a 12 volt car
battery that I will keep charged with a
Therefore, I need a timed
disconnect (probably about 10
minutes) to keep the battery alive and
the sirens from being worn out. I am
within eyeshot (1/2 mile) of another
farm, but not within real earshot, so
the sirens (one inside and one
outside) would be mostly a psychological scare to anyone breaking the
attention, whereas a pulsating alarm
— like the kind they use in car alarms
— makes people take a look see. So,
I added a second section — one that
turns the siren on for 1-1/2 seconds
and off for about 1/2 second. A single
556 IC can replace the two 555s.
Dead NiCds, May
Q. I have been looking for a way
to recharge and specifically
recondition the 9. 6 volt stick batteries
used in the older Makita series of
tools. I have the newer 18 volt De Walt
equipment, but I find that, for light
work, the Makita is easier to get into
places than the larger drills.
I purchased the better quality
recharge unit, but it doesn’t produce a
better result than the original — just
more lights. I have searched the ‘net
for a reconditioner or a good value in
new batteries, but I have not found
either. Do you have a circuit which
would at least recondition the stick
pack in order to recharge them?
Gary A. Micanek
The technology builder's source for kits, components, supplies, tools, books and education.
A. A single 555 timer would serve
your purpose. Going on your
requirements, I assume you want to
use the window foil and magnetic
door switch; that’s how the timer is
wired in (Figure 4). When the circuit
is broken, a negative pulse triggers
the pin 2 input of the 555 and sounds
your sirens for about six minutes. The
only way to reset the alarm is to
reestablish the loop’s continuity. If all
you’re protecting is a door, closing
the door will reset the alarm; a broken
window is another story.
It’s been my experience, though,
that a droning siren attracts little
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