Introduction: LED Mini-spotlights
A truck I had a few years ago had dark tinted windows and it was very difficult to see when backing up at night. I built some LED lights to mount under the bumper of my truck when I put the truck in reverse. There were a few design flaws with these, but this is how I did it.
Step 1: Gather the Materials
Each light pod will have 36 super bright (15000 mcd) white LEDs. The pods are made of black ABS plumbing pipe and will be attached to the bottom of the rear bumper on either side of the hitch.
- 2 qty - 1-1/2" ABS cap (Lowes) $1.88 ea
- 2 qty - 1-1/2" ABS street trap adapter (Lowes) $1.35 ea
- 2 qty - 1-1/2" ABS cleanout adapter (Lowes) $1.17 ea
- 2 qty - 1-3/8 x 1-3/16 x 1 rubber stopper (Lowes) $1.99 ea
- 1 qty - 3/8" fender washers 4/pack (Lowes) $1.27
- 1 qty - 3/8" hex nuts 5/pack (Lowes) $1.04
- 2 qty - #100 o-ring 2 x 1-3/4 (Ace Hardware) $0.79 ea
- 72 qty - white LED's (eBay) ~$5
- 24 qty - 120 ohm resistors (eBay) ~$2
- 1 qty - circuit board (Radio Shack) $3.99
- 1/8" thick plexiglass already had
- 1 foot - 3/8-16 threaded rod already had (later decided to use a hollow lamp nipple)
- 2 qty - o-ring to seal plexi lens (Ace Hardware) need to get
Here's most of the parts laid out.
Step 2: Build the Housings
The cleanout adapter will be glued into the cap and this will act as the back housing. The circuit board will be cut to rest on the shoulder at the bottom of the threads. The street trap adapter will thread in and "sandwich" the circuit board.
To seal this thing up, I wanted to add a lens. I'll use 1/8" thick plexiglass for the lens. I bored out the threaded side of the street trap adapter on my "redneck lathe" (pics below) to allow the lens to be closer to the end of the adapter and allow room for the LED's. This picture shows the stock piece on the left and the modified piece on the right. Note: If you have access to a lathe, it would probably turn out much better. I actually have access to a lathe, I was just lazy and decided to try it at home. If it didn't work, I'd just buy another piece.
REDNECK LATHE: (see note above) I used a 1-1/2" holesaw wrapped in electrical tape as a make shift collet. A drill bit through the work piece and the holesaw to keep it from spinning. This was chucked into my drill press. I clamped a sharp wood chisel to the work table and used the drill press quill feed to lower the part onto the chisel. Kind of the opposite principle of moving a carriage/tool post towards the chuck of a lathe. The ABS is really soft and cuts really easily. I had my drill speed set too fast and it was starting to melt instead of cut. After I got the diameter and depth cut the same on both pieces, I actually used a thick steel ruler to square up the shoulder of the bore with the custom collet chucked into a hand drill. Like I said, this stuff is really soft and cuts easily.
Here I've got the circuit board marked for cutting (pic 9). I drew up the pre-drilled circuit board layout on AutoCAD to figure out how I was going to layout my LEDs on the pre-drilled board.You can see the template I printed out.
I cut of the smooth end of the street trap adapter and sanded it smooth (pic 12). Here it is threaded into the cleanout adapter with the circuit board sandwiched between the two. Notice the shoulder for the plexiglass to rest against in the first and last pics.
Plexi taped off and marked for cutting.
Exploded view of the pieces (pic 13). The white tube on the right side is the center tube from a roll of taillight lens repair tape. I will cut it down to proper length to sandwich between the circuit board and the plexiglass lens. This will keep the lens sealed tight against the o-ring (not pictured) and spaced off the LEDs. I thought about just gluing/siliconing the lens in, but would like the option to replace the lens in the future if needed. ***Could be adapted to accept a red or amber lens for extra brake or turn signal lighting***
To reduce vibrations, allow for adjustability, and provide enough clearance to get all the way below the bumper, I'm using rubber stoppers. They are 1" thick and provide the perfect spacing. The rubber is fairly soft and will form around the light housing once tightened down. I needed to get a hole in these so I used a piece of 3/8" steel tubing. I sharpened the inside diameter by using a combination of a rat tail file, countersink bit, and a regular drill bit (pic 14). Once the inner diameter was sharpened, I chucked the tubing into my cordless drill and centered the tubing on the stopper. I "drilled" into the stopper from both sides. I then used a bench vise, a large socket and a washer to "punch" the tube through the stopper. It's not the cleanest hole, but I knew a regular drill bit would never cut through the rubber. This worked better than expected. Besides, no one will ever see the inside of this hole.
Here they are fully assembled (pic 18). The housing was drilled and tapped for the 3/8" threaded rod. I thought about using a jamnut to keep the rod from backing out of the plastic, but the rubber stopper does a good job acting as a jamnut when installed on the truck.
Here is one of them installed (pic 20). The other will be evenly spaced to the other side of the hitch. The threaded rod runs up through factory holes in the bumper. A fender washer on top of the rubber stopper keeps the top of the stopper from deforming, but the bottom of the stopper conforms to the curvature of the housing. A fender washer and nut on the top side (inside) of the bumper sets your tension on the stopper. The elasticity of the stopper will keep the threads from coming loose, as well as dampen vibrations.
I used spray-on bedliner to coat the housings for a uniform appearance.
Step 3: PCB Etching
There's a lot of online resistor calculators that will help you determine the resistance needed for the number of LEDs you'll be using. Here's the array of LEDs that will be in each housing for my project. I designed the circuit to run on 12V so it can be hooked directly into the reverse light wiring. Both lights together will draw less than 0.5A.
The circuit is just under 1.75" diameter. The center pad will be ground and the pads at 6 & 12 will be positive. All components are through-hole (LEDs & resistors). The resistors will come through from the backside and the LEDs will go through from the front. Now to try my hand at toner transfer etch masking...
The circuit layout that has been laser printed on glossy paper. Laser print toner is resistant to the etching chemicals. This is placed face down on the copper clad board and ironed on like a t-shirt transfer. I cut the board out before etching.
Etching process: you can see the black stuff running off the board in the 8th pic. That's the copper that is being dissolved by the chemical. The 9th pic you can see a ring of copper that has not dissolved yet.
All that is left is to clean/sand off the resist material (toner transfer) and drill the holes.
Step 4: Make 'em Stick and Glow
A bunch of LED's ready for solder. Test fitting resistors on the backside of the board. Testing as I go...
Step 5: Final Touches
I changed my design slightly to accommodate the wiring to run through the mounting stem. I went to my local Ace Hardware and got a 5" long lamp stem (nipple). It's basically a threaded tube that is used to support and run the wires up to a lamp socket. I picked the 1/8 IP (which is basically 3/8"). I used a 23/32" bit to drill out the hole that I had previously tapped for the 3/8-16 thread. It was a snug fit, but the lamp stem threaded in, cutting its own threads as it went along. I figured if I couldn't get it threaded, I'd break out the big soldering gun and heat the nipple while I threaded it on. Plastic is so easy to work with :) I got them both threaded in and assembled.
Now for a little testing using a 12v wall wart. Pic 5 is behind my house with no lights on. Drum roll please... A mighty 2.8W of powwwerrrrrrrrrrrrrrrrrr (pic 6)!!! OK, maybe its not that exciting, but I'm extremely pleased with how these turned out...but there were a few design flaws with these:
- I failed to seal around the lens, and after a few trips through the carwash, there was enough corrosion that killed about 1/2 of the LED's.
- I made the contact pad for the +12v supply far too small.
- Even with a strain relief, the power connection eventually broke off the board.
- No heat-sink. While your reverse lights are not typically on for very long, these still get pretty warm. Pair that with no circulation and the problem compounds. I didn't have anything melt, but the heat shortens the life of the LED's. On a different system (non-vehicle), these could be ran at a lower voltage - thus eliminating the resistors which would help with the heat as well.
I've thought about building another set of these for other projects using surface mount resistors and surface mount LED's and a two sided board so everything is not so cramped, but I recently discovered that I can get two 10w waterproof LED spotlights in aluminum housings (made for fountains and pools) for under $20 on eBay.
I enjoyed making these because I had to think out-of-the-box to get these made with everyday materials and common tools. If you like this instructable, please vote.
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