Q&A
■ WITH RUSSELL KINCAID
In this column, I answer questions about all
aspects of electronics, including computer hardware,
software, circuits, electronic theory, troubleshooting,
and anything else of interest to the hobbyist. Feel
free to participate with your questions, comments, or
suggestions.Send all questions and comments to:
Q&A@nutsvolts.com
WHAT’S UP:
Join us as we delve into the
basics of electronics as applied
to every day problems, like:
Blinking Tail Light ✓
● Geiger Counter
Mailbag
✓
✓
LOW VOLTAGE
WARNING
QI am looking for a low voltage warning system for an antique Delco light plant. The Delco light plant
has two 12 volt and one eight volt
lead acid batteries in series for a total
of 32 VDC. As the voltage drops
from running the lights, you start the
plant and charge the batteries back
up. The problem is if you let the
voltage drop too low, you don’t have
enough battery power to start the
plant again. I would like a warning
system to incorporate an LED strip
and buzzer. Fully charged, all LEDs
are on and the buzzer is off. As the
battery voltage drops, each LED goes
off until they are all off at which time
the buzzer comes on (approximately
28 volts) to get your attention. I
would like the voltage points to be
adjustable by replacing resistors.
AThe LM3914 bar graph driver was made for this application; it has the voltage divider,
comparators, and current source
output to light 10 LEDs. The resistors
are not adjustable but you can adjust
the upper and lower voltage of the
display. The LM3914 has linear
increments, but if you prefer, the
LM3915 has logarithmic increments.
■ FIGURE 1
ENERGY
COMPUTATION
QI am trying to find the nergy in an inductor but my math is obviously wrong. I
won’t be offended if I find that I
have been taking a completely
20
June 2010
