LED lights

[Jay2TheRescue]

I know instrument panel lights are the worst. In the past I would buy about 2 dozen bulbs if I had one burned out and just replace all of them while I had it apart. The first time I tried to replace a bulb on the panel I just replaced the burnt out bulb. A month later 3 more bulbs were dead and I had to take it apart again. I have 2 or 3 burned out on The Beast, but I haven't been bothered too much - the DRL indicator is burned out and a couple of bulbs in the radio are gone. My preset buttons don't light anymore. I'll wait till one or 2 more go then take the whole thing apart.

-Jay

[theholycow]

Most of the lights in my GMC's stereo are out. In the time it took them to burn out, I got so used to operating it that I don't need the buttons lit or even labeled anymore.

[Jay2TheRescue]

yes, I can operate my stereo without the lighted buttons, I'm just being anal-retentive about it. There's something that doesn't work exactly right. I honestly think I suffer from some kind of OCD.

-Jay

[itjstagame]

Remove all the lights, much savings compared to changing to LEDs :-).

Anyway, for you electronics and LED wizards, I want to take the LED plunge. I'm starting with dash lights and radio lights because I don't want to trace out the brake and blinker wires and construct bulbs yet.

I found out that one superbright white LED is plenty compared to an old dash indicator light and they're very directional indicators (the idiot lights that is), so I really only want one/light. So I tested and found out all my idiot lights are ground switched from the ECU with a common positive. So it'd be really nice to just change this positive rail to the 3.5V required for the LEDs and be done with it.

What's the best way though? If I'm using 4 LEDs in series I don't mind putting the resistor in for added protection because it's such a small amount of power loss for 4 LEDs, but I would think that the power loss from big enough resistors to create a voltage divider down to 3.5V to drive multiple LEDs would be more substantial. I don't want to change these for fun or for looks, I want less energy draw.

So I was thinking about maybe a small transformer, 1/4 step down would turn my 14.4V to 3.6V and the 'off' ~12V to ~3V (the leds are rated 3.1-3.6V). The question is, what number winds/size would I need and can I ground it to the 12V source? That is have the transformer and battery have a common ground so I don't have to change over the ECU ground for the switching?

Now that I think about it though, I was only planning on 4 LEDs for lighting the dash itself and 4 for the HVAC controls, plus 8 idiot lights, so that's 16 LEDs max in use at once at 20ma each, so we're only talking .32A total, which I guess won't draw too much across a voltage divider and waste too much heat at the resistors. What wattage do you think the little bulbs are? 3-5W ? At 3W that'd be 3.3A, so I'm saving 3A already, woo!

All I know is right now when I turn the parking lights on I can definately hear the engine idle down under load and that's just parking lights. I want to reach the point where this doesn't occur anymore.

[Jay2TheRescue]

I don't know about a transformer. This is what I would use:

http://www.radioshack.com/product/in...entPage=search

Its a solid state adjustable voltage regulator. Its cheap, compact, reliable, and easy to wire up.

-Jay

[theholycow]

Why reinvent the wheel, engineering your own ways to make invidual LEDs replace automotive bulbs using transformers and such, when there's already inexpensive plug-in direct replacements?

[itjstagame]

Because they're prohibitively expensive and not as energy efficient as they could be. Enough LEDs to do what I want is <$10 shipped on ebay as are transformers, resistors, etc. When I looked at superbrightLEDs, $10 wouldn't even get me two bulbs.

Jay, as for the voltage regulator, it looks like the same problem. The output voltage is based on the resitor you chose which is directly based on how much current you're going to flow through it. So if one idiot light is on and I tuned for 20ma then it's ok, but if two come on then my calculations will be off. I basically just want a 3.5V source with 0-1A available.

[theholycow]

Originally Posted by itjstagame

Because they're prohibitively expensive and not as energy efficient as they could be. Enough LEDs to do what I want is <$10 shipped on ebay as are transformers, resistors, etc. When I looked at superbrightLEDs, $10 wouldn't even get me two bulbs.

Good point. We're here to save money and figure out new, better ways to do the same old stuff...so how would LEDs be an exception to that? They wouldn't!

[itjstagame]

Ok, I just looked and maybe that would have been easier for the dash lights. They have #74 bulbs for $1.79 for a single superbright (amber though) (which is what I'm doing) and $2.79 for a more multi directional one. Realistically I probably have 8 idiot lights or so, so that'd be $14.32. Instead I've got an LM317T, some resistors and 8 LEDs, so probably $5 if I try hard. But I've put much more time into this, probably over 3 hours already, maybe heading toward 5, plus I still need to figure out how to 'wedge' them into the bases and I have to keep track of + to - direction (not sure if the superbrightleds.com place has to do that still do or has some special circuit).

I would think if they've got a single LED they must have a voltage divider inside each one. I'm not good at calculating how much energy would be lost through such a thing, at the 20ma a single LED draws I'm sure it's not much. I kind of feel like my way is 'cleaner' as far as number of components and layout, but certainly not in the easiness or looks department.

Anyway though, as you said, I actually only have $6 in my pocket now until next pay day and $14 (though not expensive at all) would have been more than I could handle just for some idiot lights. Besides I doubt the wattage savings will ever break even, even at $5 :-). Of course I don't have any free time and am getting a lot of flak for always working o nthe 'broken' car. I don't have the balls to try to explain I'm really just hacking apart a perfectly good car :-).

EDIT: Meant to say also, the $6+/bulb is for the standard 1137 parking/brake lights, etc. Since I'll be using 20 or so LEDs on these I can just use standard 4 leds + resistor circuits in parallel, so all I need to so is lay them out on a protoboard and shove them into a standard bulb socket and solder like crazy. 100 superbright red LEDs (for tail lights) were like $7-8 shipped and came with the resistors. So I'll easily be saving $30 across the 6 bulbs and shouldn't take much work. The dash is the bigger headache. Although I am planning on a new electronic flasher and probably a dimmer circuit and need to trace and figure out where to wire in.

Jay, btw, LM317T was an awesome suggestion, it's putting out 3.47V whether car is on or off and will handle up to 1A (50 LEDs). The only thing that sort of stinks is I will probably have to make another one for the dash/parking lights because they're on a seperate circuit through the parking light switch and dimmer control. That is unless I really want to trace wires like crazy and hack new circuits to save on a few components....
http://ourworld.compuserve.com/homep...den/page12.htm
Any idea why they'd want a 22k uf cap there? I left that off because I could FIND one, the 2,200 uf caps are D cell size and expensive as hell. Works fine as is.

[itjstagame]

One last thing. Cow's comment about learning a newer/cheaper way to do stuff made me realize I should really document this stuff. For fun and to maybe help someone else. Here's a demo of what I've typed up so far. It'll look much nicer with pictures and moved to a proper .com, but please let me know if you think I've left anything out or see any typos: http://dax.prolixium.com/~itjstagame...s/dashled.html