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How To Make LED In-Car Christmas Lights
What This Is
For some years now, I have had a homemade string of Christmas lights in my car which was adapted to run from a cigarette lighter adapter. I updated them recently to use LEDs; here's how to do it.
The lights are alternating red and green LEDs with a ping pong ball around each LED. They are bright enough to see well at night, but not so bright that they interfere with your vision or attention while driving. They can be turned off simply by unplugging the adapter from the cigarette lighter socket.
The string of lights is Y-shaped. The "tail" of the Y has the power plug which goes into the cigarette lighter socket. This powers the lights when the car is on. A bit of tape ensures that the wire stays out of the way and helps ensure that the results are sufficiently ugly and home-made looking.
"arms" of the Y go from behind the rear-view mirror,
across the base of the sunshades, and then back across the tops of
the doors. I tuck the wires under plastic borders to the
upholstery and use twist ties wherever necessary to hook or
otherwise attach the string of lights in place. In total, there
are 12 lights (6 on each "arm") which reaches just far
enough around the car's interior to reach the rear windshield.
How They Are Made
The following items are needed:
Power comes from the accessory plug (about 12V or a little more), will go through the 47 Ohm resistor, and the LEDs will be wired up in parallel.
If you wish to play around with the number or type of LEDs, or the wiring, you should make sure your resistor is appropriate and your wiring layout is good. An LED calculator (there are many on the web - here is one of them - can help you here.)
Assembly is simple, but requires attention to detail since a mistake can - at best - result in a Christmas light string that partially or wholly doesn't work - or at worst, a short circuit being plugged into your car's electrical system.
for a larger version.
Building the LED String
First, it may be useful to measure out the cable inside your vehicle and mark off where you'd like the bulbs to be and how long you'd like the cable to reach. If you don't particularly care, you can just space them more or less evenly.
select a spot for your first LED, separate the wires if required,
and strip a piece of the two wires so that the conductors are
exposed. You don't need to actually remove the insulation from the
wires entirely - you should be able to just push them aside enough
with a wire stripper so that you can solder the LED to the
bend the leads of your selected LED as shown. The longer lead goes
to what will be the "-" wire. It is critical that you
are consistent! All short leads of all LEDs should go to the same
wire (and conversely, all longer leads should go to the other
solder the LED onto the wire. Make sure it's securely soldered.
cut a small hole in a table tennis ball - big enough for the LED
to poke through.
secure the ball and the LED together (and cover any exposed wire
and LED leads) with hot glue.
one light! Repeat until you have all 12 LEDs installed and
secured. Then you can test by hooking the string up to a +12V
source through the resistor. If all of them light up, you're set.
(Otherwise, inspect the connections of any that don't light up.)
Building the Accessory Plug
There's not much to say here - just put the resistor in series with the "+" terminal wire (putting it onto the "-" wire will also work, but I like to put it on the "+" personally).
Then the + and - should connect to the appropriate wires in the middle of the LED string we made. This results in a "Y" shaped string of lights, with the accessory plug hanging from the middle of the string. Remember that the resistor is expected to get warm (perhaps quite warm) so don't use anything that will melt as part of insulating or anchoring it - hot glue would be a no-no.
Hook it Up, Cruise Around!
Light it up by feeding +12V into the adapter plug, and after one last check that all the LEDs light up properly, Install it into your car!
(From past experience these get attention when going through a drive-through.)
And speaking of LED Xmas lights, you may also wish to check out my miniature USB-powered LED Xmas Tree with blinking lights!
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