LED Needles writeup
Well here it goes. This took a ton of labor to perfect. I'm no wiring genius and until this my circuit prototyping experience was practically zero. I'd worked on basic breadboard projects in my electronics 101 engineering course, but that was about it.
First, for a perspective, these are the SMT LED I'm dealing with.
They are far from the smallest available, but are plenty small for this project. They are a 1206 package. Digikey part number 160-1167-1-ND. I got 50 of them for under $5 a year ago thinking they might come in handy at some point.
This is my power source. 8 1.5 AA batteries in series. That makes 12V for those scoring at home.
And just for shits, a picture of my garage. Nothing special, but I love it. It's a rental, but if I owned it you'd see finished walls, epoxy floor and wall storage galore. But alas, I'm still young so home ownership isn't under my belt yet and my garages are pretty basic.
So the gauge lighting concerns starts with the fact that once you update the face lighting with LED's, the needles fail to glow as brightly, especially if you pain the needles. I wanted a crisp white face and deep red needle. This means White leds in the face and red SMT (surface mount technology) LED's or SMD (surface mount diode). Mine were roughly 1mm tall which means they can fit between the gauge face and the component behind the gauge. The amount of clearance available varies from gauge to gauge. The speedometer and oil pressure gauge likely have the least amount of clearance. They were the most difficult for me. The easiest is probably the tach.
So onto design. I started with a search for a substrate. Having no experience with circuits I was lost. All i knew was I needed something very thin and something that I could stick some LED's to. To try my plan I and to make sure the LED's would light the needle correctly, I started with cardboard and an old credit card. LED's worked and lit the needle perfectly. The cardboard and/or credit card as a substrate was a horrible idea, but you probably could have guessed that.
Somehow I lost a ton of photos which would have shown exactly how I made each circuit board. At some point I'll add them back in if I find them. For now, I'll have to skip some pictures and bore you with words.
Before actually doing anymore building I measured the hell out of the gauges and the mounting areas. I measured everything in inches and to an accuracy of 0.01". I wasn't able to hold that same accuracy during the build part, but the accurate measurements were definitely helpful. The only gauges that were similar were the water temp and gas gauge; and even those had minor differences if i recall correctly. Once I had all my measurements I modeled the baords I had in mind in SolidWorks (CAD).
The above drawings should be right, but I had to make adjustments and I'm not positive I went back to edit all the cad files. So use that info at your own risk, lol.
Once I had everything modeled it was time to start building. A pair of locking foreceps was key to soldering with the SMD's. My soldering iron is a basic POS and made this more difficult that it could have been with a good iron. I found some proto board about 2 inches square and 2mm thick. I used a dremel to cut the boards into the correct size and then proceeded to start the wiring. The pieces all needed to be pretty thin. The speedo especially has very little clearance and has a very delicate piece of the gauge directly underneath where the LEDs are mounted. This means you have to be very sure your LED inserts will not touch the instrument. The needles on all gauges are very delicate. Any slight rubbing means the gauge is worthless and you have very little margin for error.
I had a great picture of the speedo showing exactly how tight it is, but I seem to have lost it. Imagine a very small space....
The smaller gauges all have a light guide system that relies on the face lighting to carry into the center of the gauge face, where a semicircular extrusion of clear plastic grabs the light and throws it out onto the needle. Clever design, but unfortunately it wont work with what we're doing and you need to cut it off. I used a dremel and was very, very careful.
Below you can see the difference between pre 89 (my prototype dash) and 89+ (My actual car). The pre 89's have a TON of space for the needle to catch light from below. The 89+ on the left have just a small square (green arrow) to catch light for the needle. This affects how much light is needed and determines whether or not you need to drill out the gauge plastic to let more light through. My proto board (pre89) was fine leaving the plastic backing alone, but on my actual car (89+) I had to drill out the plastic entirely underneath the needle.
This is what I'm talking about:
Left alone:
Drilled out:
In the picture above you can see how the LED's are mounted. It's pretty basic, really. You just need to measure everything and know where you need to center the LED's.
Here's the Speedo finished:
And here's what the board looked like more or less when I was done with the speedo. I had to use my dremel drill press as a mill and mill a channel for the wire. The clearance was so low that the board plus the wire (22AWG) was too thick. The problem with the speedo is that you cant have anything hanging down under the board, so the wires cant be underneath, they have to be on top.
This is the speedo unit. That coil is the gauge and is incredibly sensitive. Nothing can touch it.
Just for shits, here is the oil pressure gauge. I dont understand how the gauge actually moves, but the whole thing is so flimsy I just cant grasp how it could be very accurate.
Here is one of the small gauges after already having shaved the bottom of the needle base. Clearance are very, very tight. You want to keep this clearance minimal so you have less light escaping from the center of the gauge. Light bleed will be noticable when you use two different colors for the needles vs gauges.
Continued in another post since I think i'm getting close to the one post pic limit. This will all end up in the lighting thread as well.