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Like the cool underglow kits on riced out cars but don't want to break the bank? This will show you how to make your own using LED strings.

Indications:
-This instructable requires some knowledge of electronics and auto body assembly.

-This might involve taking apart large sections of your car's console, if this could void a warranty, do so at your own risk.

-In some states and municipalities, it is illegal to have non-signal lights on while your vehicle in motion. Check with your local authorities before using on the street.

Time: 3-6 Hours
Cost: $20-50 (depending mainly on how many lights you get)
Difficulty: Decently easy
 
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Step 1: Gather materials

Picture of Gather materials
Materials:
-One or several waterproof, 12V LED strings - $10 ea.
-Lots of wire. Two-strand polarized wire is great (red-black or white-black)
-SPST switch - Free-$3 (I got a lit-when-on one)
-555 timer - $0.10-$1.50 if you went to Shady-o Rack
-10000-15000 uF worth of 10v capacitors (you can string them in parallel to add the capacitance)
-47uF capacitor
-100uF capacitor
-.01uF capacitor
-1.1kOhm resistor
-15kOhm resistor - the bigger the resistor the slower the pulse - alternatively you can use a potentiometer
-Project box of some sort
-Scrap thin medium-density fiberboard (MDF) or sheet metal
-Epoxy
-Electrical tape

Tools
-Soldering iron and solder
-Wire strippers
-Needlenose pliers
-Hot glue gun
-Power drill
-Various size drill bits
-Various screwdrivers

And of course a car. It's a good idea to know your way around the inside of your car a bit before beginning.

Step 2: Take apart your console

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Easier said than done. You have to basically remove enough panels to get at the wiring of the car's cigarette lighter or auxiliary power. Next, find a suitable spot for putting in the switch. I like using one of the blank buttons near the headlight controls. It's a good idea to drill the hole for the switch while everything is all apart.

Then, since you're probably already under the steering column, look for an unused plug in the firewall, right by the fuse box on most models. This is for running extra wiring (like we're doing) and, once you pop out the plug, should lead to somewhere near the left front wheel well. Save the plug, you'll need that later.

Step 3: Add an auxiliary extension

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Find your 12V power line. This is usually the red or white wire that goes into the housing for the cigarette lighter socket. Then, find the ground, a black wire most likely attached to the outside metal of the socket. Cut or expose the insulation from both and splice in the red (to 12V) and black (to ground) wires from the double strand. Cut the wire so that it's long enough to reach the switch and then some just in case. It's easier to cut wire than to extend metal and plastic using telekinetic ability :-).

Step 4: Install the switch

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Take either your positive wire or your ground, and wire it to one of the switch terminals. I used the positive just out of force of habit. Then, add about 6" of double-stranded wire to this (red to the switch and black to the other black wire). This will later connect to the controller circuit.

Step 5: Affix LED strands to the bottom of your car

Picture of Affix LED strands to the bottom of your car
The layout is pretty much up to you, you can have a strand for front, back, left, or right, sides only, front and back only, all sides, whatever.

Make yourself some 2" squares of MDF, two per strand, and epoxy one to each end of each strand. Let that cure.

In the meantime, you can pick out suitable spots to place the strings under your car. Anything that is directly part of the chassis is great. Be careful not to put it too close to the engine or exhaust line! If you want a more temporary attachment, you can bolt the MDF to it or hot glue it for semi-permanent. A liberal amount of hot glue seems to bond the MDF to the metal really well; I've driven 100 miles with my setup and it hasn't fallen off yet. I wouldn't recommend using epoxy or J-B weld in case you have to take it off for whatever reason.

Step 6: Wire the LED strands

Picture of Wire the LED strands
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Remember that hole in the firewall from step 2? We're going to use that now. If your car doesn't have a vacant one already, either piggyback one that already has wires going through it or drill your own hole.

Since every car is different, you're going to have to come up with your own way to snake some double-strand wire from the cabin to the bottom of your car. Generally though, there should be an opening straight to the bottom near the front left wheel well (for countries that drive on the right, it'd be the right wheel if you're across the pond :-P). Tie a loop of string around the end of the wire, then feed about a foot of the wire through the hole. You should be able to see it when you look under the hood.

Take a coat hanger, or perhaps using your hand, grab the end of the wire from underneath your car and pull it through. Duct tape it to the bottom of your car to keep it from going anywhere (you can take off the loop now).

Run wire from each of the LED strands and wire them all in parallel (red to red, black to black) and solder the whole mess together. I'd recommend using liberal amounts of electrical tape as well. Once again, stay away from hot components.

Make sure to leave 1-2 feet of wire inside the cabin.

Step 7: Circuit time!

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If you're at all savvy with circuit boards this should be cake. This circuit creates the pulse effect, if you want just a continuous light, you can skip this.

The idea is the 555 timer generates a square wave which charges up the capacitors in the on phase. In the off phase, the capacitors light the LEDs, depleting over time and creating the fade out effect. Theoretically, during the on phase, the current used to charge the capacitors should detract from the LEDs, creating a fade in effect, but often the current is so large that this is nearly instantaneous. Alternatively, you can put in a switch that bypasses the pulse circuit (so that the ground from the LEDs goes straight to the mains ground) so you can go from pulse to steady on.

I more or less used capacitors and resistors that were lying around. You can customize the frequency using the 555 timer calculator. Alternatively, you could sub in a potentiometer for RB to get a variable rate.

The 12000 uF capacitor is just a bunch of large 12V capacitors wired together. You may need more or less depending on the number and rating of the LED strings to get the right effect.

Test out the circuit on a breadboard connected to the car's electronics before putting it onto a PCB. And then test it when you've soldered it before boxing it up.

Step 8: Installing the project box

I didn't feel like buying a project box from Shady-o Rack, and since this thing is gonna be tucked up under my dashboard, I frankly don't care. So I made one out of MDF and hot glue :-P.

I put two screws on either ends for the power, ground, power for lights, and ground for lights, so I could just screw on the wires. Make sure to leave enough on the inside to account for the twisting (and start with the screws nearly fully tightened when you solder).

Find a nice comfy spot somewhere up under the console to put it. Screw down each of the wires to their respective contact, and tape the box securely so it won't rattle around.

Step 9: End.

Wait till night falls and enjoy your handiwork.

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InvizibleAlex10 months ago

Can you hook up a switch so you can turn the underglow on or off? Turn it on only on ocasion and so that you can avoid trouble with cops in the states where it's illegal?

DeusXMachina (author)  InvizibleAlex10 months ago
Yeah, mine had a switch in the dashboard.
hey ! i was thinking of connecting a TIP31 transistor to these chains of leds and than sync it with music... do u think it'll work out ? is the power (audio) signal 4rm a cell or mp3 enough to light up so many leds or should i b using a audio amplifier circuit ?
hicecilia3 years ago
This is sick.
soramac3 years ago
I have for sale:1 LOT 0F 6 TIREFLYS



Make your car or motorcycle glow, can be mounted virtually anywhere, easy to install, 12v power required, connects to an accessory switch, cables included

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Mikey85675 years ago
One thing you could do to make the LED's last long is to take a piece of clear vinyl tubbing (large enought to slide the LED strip in) and once you have it pulled inside then seal the ends with you choice of sealant. This will not only keep the LED array from getting damaged from rocks, salt (if you live in northern states) and other things that would break or ruin it, but you would also make it much easier to clean off the road grime your going to get from every day driving, imagine trying to wipe between all the LED's and such (would be a real pain).  The tubing would slo make it eaiser to mount under the car (IE hose clamps, epoxy, zipties,  ect).
Great idea! That's perfect and a cheap solution to a potentially big problem.
The vinyl tubing can be bought from most hardware stores in sizes from 1/4" to 2". As far as zip ties make sure that the black ones are used, they are UV resistant and last much longer and don't get brittle like the clear or white ones do.

As far as sealant make sure it doesn't react badly to vinyl, some discolor it.
Depending on your car is how the wires are... Most cars only have 2 wires going to the ligher, and some are swithched. Most cars the top is negative (-) and the center is positive (+) Also you may have to upgrade the fuse that is there, since that line also takes care of a lot of different things on your car... ie.. Dome Light, Clock on the radio, ect... Things that are not needing power all the time, and some have a switch on them so you don't have to have the key in the igntion, and to the on position to get them to work. I would recommend getting a book on your car, or goto the library and finding a book on your model to get specs on it. I personally would run 2 seperate lines, 1 to a barrier strip from the Acc terminal, and then the second one to another barrier strip to run a ground wire from the engine comparment gives you a neater look, and less problems if you want to add or remove anything. Spend a few extra cents, and do it right, less problems in the end.
would it be possible to remove the lighter thingy (as a non-smoker its always appeared more of a weapon than anything,....) and just put a switch there, and use the wires that held the thing in place to power the leds?
Thats dumb. It can be used to charge your cell phone and other stuff. why would you want to remove it? a bic lighter is more of a weapon. do you never walk into a gas station?
Sorry if I've never needed it - and perhaps weapon was a poor choice of words, more like 'hazard', either way - I'd rather just have the switch, but given I cant remember in the slightest what this instructable is about - I honestly don't care what you say :D
mdeep4 years ago
please just dont. this is tacky!
PSPerson4 years ago
too bad its illegal in my state. *sigh*
Jaycub4 years ago
What does 1337 mean?
leet
rumarch Jaycub4 years ago
LMAO
it means your not 1337. for you, it means 14.
Hi i do all of these works on the board but there is no pulse on led. what can be wrong ? all the things is correct
hi there, i know its been 3 years from the last reply, but i allways wanted to add the pulse affect on my undercar neons. 
And that's my question, i have installed neons and not leds. can i somehow connects your "pulse generator" to my neons to have that effect?
thanks
DeusXMachina (author)  HYPER_piccolo5 years ago
Umm, I don't think neons would work with a pulse setup like that, because they need a constant voltage. It would have to be built into the setup, I think. But LEDs, lights, and certain fluorescents work.
yes, i asked a friend who is very good at electronics and he told me the same thing, so i guess i will make something with leds :)
thanks
senario 1586 years ago
what about my car?
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I love a clean Fairlady..... What year is your car?
yo man5 years ago
paul waker rides again
yo man6 years ago
or run a hot wire to the positive post on the battery clamp. I like to run the wire past the door opening to dash.
But that's unecesary... The only time that needs to be done is for an amplifiers power line. Otherwise it just looks ugly under the bonnet and is a waste of wire.
well it is way easer to do or yo could find a opening in
the fire wall
jobergy6 years ago
it would be fun to dink around with it enough to make it pulse to your car stereo music???.....maybe a next instructable lol
Simple just direct connect it to your speakers it should pulse to the sound of your music. Or you could use a pulsar XV2
ok i tried direct connecting it to my speakers, but it didnt work, no lighting even, sound was on but not the lights, so a pulsar i al guessing is a sound sensor?
 
k0ldburn5 years ago
What about EL wire? Is it not powerful enough for this? I've never experimented with it but it looks like a good solution
mazeka.146 years ago
can you skip this step if you just want continuous light? or does this modify the amperage or voltage?
DeusXMachina (author)  mazeka.146 years ago
Yeah you can skip all of that if you just want the lights on the bottom of you car. The box just makes it pulse.
awesome, thanks
armoandrew5 years ago
you have to use a transistor something like a TIP31 transistor but it depends on the amount of current you have coming through your lines

they can be found at your local shady-o-shack : )
brentonl5 years ago
Couldnt you use the 555 to PWM the brightness of the lights? 
pmac937 years ago
you put underglow on a minivan? that is solid man.
Dr.Paj pmac937 years ago
Under body lighting adds 50hp, so why not? Everybody knows that.
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