64 March 2017
the sender only, not advice as to what
you should do.
Mt Airy, MD
[#11163 - November 2016]
I sometimes forget to turn the
headlights off on my car, so I wake up
to a dead battery and a late start to
work. I would like to build a DIY auto
headlight on/off switch. Anyone have
a schematic or design?
#1 Typically, the easiest way to do
this is to connect a diode, a suitable
resistor, and a sonalert from the
headlight switched positive to the
RUN position of the ignition switch.
If the headlights are left on when
the ignition switch is turned off,
the sonalert will sound. The diode
prevents the sonalert from sounding
when the car is running and the
headlights are off. The resistor scales
the 12 VDC to a lower voltage for
the sonalert if necessary. This is much
simpler then an automatic switch, and
it consumes no power.
The Villages, FL
#2 You just need a 12 volt SPST
relay. Wire the contacts in series with
the headlight power wire and power
the relay from the ignition switch
accessory terminal. You may have
to find it by trial and error among
the wires coming out of the steering
column, or an auto repair manual may
tell you the color of the wire.
#3 After a couple trips across town
to jump-start my wife’s car, I installed
a relay to automatically turn the lights
off when the ignition was turned off.
All you need is one of the generic
automotive 30A relays. If you can
find the power wire to the headlamp
switch, cut it in a convenient place
and put the contacts of the relay in
series with the headlamp switch.
Then, connect the relay coil between
a switched 12V source (turns on/off
with ignition) and ground. The lights
will only work when the ignition is on.
If the power wire for the
headlamp switch is inaccessible, then
remove the headlight fuse, and get a
relay and an inline fuse of the same
value as your headlamp fuse. Then,
connect the fuse to the hot side of
your original fuse holder, the other
side of the fuse to one of the relay
contacts (usually 30), and the other
relay contact (87) to the other side
of your original fuse holder. The coil
connections will be as above.
>>>YOUR ELECTRONICS QUESTIONS ANSWERED HERE BY N&V READERS
SHAPING THE FUTURE
The future of unmanned systems and robotics technology—and the
exciting potential it represents—is about to take on new heights, depths
and go everywhere in between. What shape will your opportunities take?
Bringing together 650+ leading suppliers showcasing their latest
technology solutions, AUVSI XPONENTIAL 2017 is where you will see
the future of unmanned vehicle systems up close and do business with
the ground-breaking companies at the forefront of innovation.
Air | Software | Startup
IN TERNATIONAL PAVILIONS
Canada | China | France | Spain
Robots in Action | Solutions Theater
Poster Presentations | The Starting Point Theater
FIND OUT WHAT’S COMING. Register Now at XPONENTIAL.org