>>>READER-TO-READER QUESTIONS AND ANSWERS
ters in car alarms. If you are interested
in doing this with microcontrollers,
"ADXL202 CAR ALARMS" (no quotes)
to find the application note.
[#12062 - December 2006]
I have a 12V 20W-halogen light
that I want to use in my car by plugging
it into the cigarette lighter receptacle.
The alternator produces 13.8V to
14.1V. Can I just connect the cord to a
cigarette lighter plug or do I need to
reduce the voltage to 12V? If I need to
reduce the voltage, could someone
suggest a circuit that I can fit into the
cigarette lighter plug?
#1 The halogen lamp will work fine
on 14 volts but the life is inversely
proportional to the applied voltage, so
if you want to extend the life, install a
one-ohm, five-watt resistor in series.
#2 There is no problem plugging
this directly into the cigarette lighter,
especially if you are going to use the
light without the engine running.
However, if you intend to use the light
with the engine running and are
concerned about lamp life, you
can drop the voltage using series-connected silicon diodes. Since you
have a 20 watt light, you will need
diodes that can carry at least two
amps; 20 watts / 12 VDC = 1.67 amps.
A readily-available part at RadioShack
would be three-amp diodes; Model
1N5402; Catalog #276-1143.
The typical drop across a silicon
diode is usually specified at 0.7 volts.
However, at this current, you will probably find the drop to be a bit more.
There will also be some voltage drop
in the wiring itself. Two or three diodes
in series placed between the cigarette
lighter and the lamp will drop the
voltage to approximately 12 VDC.
Remember the diodes must be
connected with the proper polarity.
No damage will be done if you
accidently hook them up backwards.
In that case, all that will happen is the
light won't work. Just make sure they
are connected in series with the lamp
and NOT directly across the battery as
shown in the diagram!!!
K3PGP - John
[#12064 - December 2006]
How do I interface a VGA monitor
to use as a color monitor with ordinary
#1 The short answer is: If you want
to do it "on the cheap,"you can't!
The "long" answer is: You CAN,
but you need a "composite to
RGBHV" video converter, and these
ARE NOT CHEAP!
VGA monitors use three separate
video drive lines: Red, Green, and
Blue, along with the separate horizontal and video vertical sync signals.
They also use different horizontal/
vertical scan rates than standard NTSC
video ( 15. 75 kHz, approx. horizontal
scan, 60 Hz vertical scan). Unless you
plan on using a MULTISYNC monitor,
you'll risk damaging the monitor and
even then the best you can get is
If you're really set on doing it,
here's an idea for a converter:
DataPro Composite/S-Video to VGA
Converter, $119.00 (www.datapro
.net/products/ CSV-955B.html). As
you can see, it's not a cheap method,
but if it's worth it to you, it's something
#2 I have been using a product for
the past year from KWORLD with very
good success. It has a standard 15 pin
VGA connector that connects to the
computer monitor. Besides a built-in
standard TV tuner, there are inputs for
composite video and S-Video.
Manufactured by: KWORLD
Mfg Part No: VS-TV1531R
UPC No: 872880886919
This item is available through
Amazon.com for $49.97:
Tigerdirect.com for the same price:
TV: Coaxial (RF)
Video 1: Composite Video
Video 2: S-Video
VGA: Eight pin DB
Output 1: VGA 15 pin DB
Output 2: Composite Video for TV
Audio 1: External Audio (RCA)
Audio 2: Line-In From PC sound card
Stereo Audio Output to Speaker
K3PGP - John
[#12065 - December 2006]
I need a 16-pin TCA280AI to repair
an auto body spot welder. It is a general-purpose trigger circuit. Are there any
companies that will sell me this chip
without having to pay the typical
$200 to $500 minimum fee for a $15 to
First try the usual hobbyist sources
for parts. Some of the common ones
are Mouser Electronics, Jameco, All
Electronics, and Global Electronics. If
these fail, some of the commercial
suppliers, such as Newark Electronics,
will fill small orders, and the minimum
order is usually about $25, not
hundreds. If all else fails, one desperation move I've used is to contact the
manuufacturer of the part and ask for
a sample. Sometimes, to keep good
public relations, the company will
send one or two for free (especially if
they think it's for a prototype that will
eventually lead to multiple sales).
[#12066 - December 2006]
As I travel the highways, I often
wonder if the road is going up or down
and by how much. One reason is that
I might typically shut the air-
February 2007 103