led lighting question

[Electro_boy]

Thanks Digibeam - I didn't realise about all of those transients in car electric systems. I've just been reading up on them. Sounds like designing any complex electronics for cars is a bit of a nightmare! And my Countach clone is going to be an electric car, which might make maintaing a nice clean voltage for vehicle subsystems even more of a problem...


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[AdrianBurton]

Digi

I am interested to see your solution, I do understand the issues that you raise.  I also believe that we are all passionate about this hobby AND when it crosses into our area of expertise it can strike a nerve.

We are all here to share ideas hopefully not to shoot them down because we can.....

Im just saying....

[Digibeam]

Nice back up, so I guess every lawyer here should offer free legal advice and every police officer here should help us out of a ticket? architects line up we need free drawings for our new barn...
I paid cash for my house when I bought it do you know why? Because I get paid to do exactly what I do... Design technology... I am not under obligation to draw up schematics just because you ask, you did exactly what I expected, turned the post around to point fingers and take some self appointed hero stance.
I pointed out why the design is not useable in a safety circuit I didn't say it won't work just that it would become cost prohibitive compared to a different circuit.
Maybe we should all go to Alan's school of low voltage certification then we can shake people down for no reason with the common belief that we are superior in every way. 

[autopro]

I would have to agree here, people should offer a solution to someone's question instead of just telling them it wont work.  If you know why it doesn't work then you should know how to make it work.  Several ideas have been presented in this thread but all of them have been dismissed.  Please offer a solution.

[SchulzeA]

Your post answered my question very clearly. Fact is, you don't know how to build the circuit. You shoot down everyone's ideas, but won't provide a real usable solution. We don't need another look into your extensive vocabulary or weird analogy, just a schematic.

[Digibeam]

Are you hiring me or is this a random question to just rouse the forum?

Dot laws also require specific angles and lens emission neither of which are part of your question, also 72 LEDs is about as specific as pointing to some place over there....
Forward voltage is a little bit important as are several other aspects of the led perhaps the mcd output?
If you think I am being difficult let me remind you of your last comment to me about puffing my chest and bragging about what I do for a living.... And my way being the only way...
The only comments you make to me in public are in attempt to challenge or offer defamatory responses, neither of which I deserve.
When you get over your agendas I will be happy to offer advice for free, otherwise I am available for hire and consultation to you.

[SchulzeA]

Tail lights. 72 LED's. 2 stages of brightness. running and braking illumination levels per Canadian DOT laws

[Digibeam]

Two very different circuits,  what's your application? What are your perimeters?

[SchulzeA]

Can you provide an electrical schematic for the proper way to connect a variable brightness LED circuit? Say for a single LED with the mathematics for multiple LED's?

This is a good thought and would work for non-essential lighting...but....

Pulse width modulation for a safety device is not a safe idea, it works fine for variable brightness but a constant current device would be the choice for a dependable led light source.
The cars electrical system puts out fantastic transients to minimal circuits and based on the frequency of the transients they would make short work of the PWM controller.
Extensive filters could work, yes and inline MOVs etc would also suppress the transients, but the resulting redundant circuitry required just to stop potential damage from occurring outweighs the benefit... And if the timer circuit failed your lights would fail completely.... Not a simple change of a fuse or bulb situation.
Still, it is a good idea for internal lights with protection as part of the circuitry.

[Digibeam]

This is a good thought and would work for non-essential lighting...but....

Pulse width modulation for a safety device is not a safe idea, it works fine for variable brightness but a constant current device would be the choice for a dependable led light source.
The cars electrical system puts out fantastic transients to minimal circuits and based on the frequency of the transients they would make short work of the PWM controller.
Extensive filters could work, yes and inline MOVs etc would also suppress the transients, but the resulting redundant circuitry required just to stop potential damage from occurring outweighs the benefit... And if the timer circuit failed your lights would fail completely.... Not a simple change of a fuse or bulb situation.
Still, it is a good idea for internal lights with protection as part of the circuitry.

[Electro_boy]

You can vary the apparent brightness of LEDs by switching them on and off really quickly (say on for one thousandth of a second, then off for two thousandths, then repeat - longer off time between for dimmer light) - it's so fast your eye turns it into the average intensity. I've only done this with an arduino and programming, but it should be a relatively easy circuit to put together with basic components. Some capacitors and a variable resistor or switch between two. Many simple noise generating circuits where you can vary the pitch with a potentiometer work this way. All that would happen when you put your foot on the brake would be either constant on light, or longer on than off periods in the switching. Just a thought...


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[Robert]

I am looking into using t20  led bulbs. Here is a sample.
 https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=js3-4Hz05ezoNM&tbnid=7ZjE_sUoZ7-K8M:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.dx.com%2Fp%2Ft20-2w-200lm-led-red-light-car-brake-light-2-pcs-12v-152971&ei=9qDpU7u1J4jl8AH-4YGABw&bvm=bv.72938740,d.cGU&psig=AFQjCNGflX9CniBfPnJ4dQ797q5Ehf4CfA&ust=1407906407947506

[lance345]

I went a bit of a different way than you are wanting to go, but I will let you know what I did/found.

I bought a whole whack of LEDs off ebay from China. They were like $3 for 100 or something crazy. I got white and red. I then did some research on resistors and bought 1000 of various for like $5. After all of this I found that you can buy pre soldered LEDs with resistors for about the same price. I felt stupid, but ah well, now I have a ton of LEDs.

I am not going with a 2 stage lighting system like you are describing. For $50 you can buy a universal sequential module off ebay so I bought 4 of them to mess around with. The instructions are terrible but with some trial and error I got them working. Same as mustangs.

So overall I have premade 12V LEDs and sequential taillight modules. I have tested it out and so far it has never blown. My front signals are LEDs also. I understand what others are saying about a minimum brightness and it would suck if my lights all blew randomly but if that happens I'll deal with it. I am considering leaving the normal bulbs hooked up hidden in the trunk and splicing off the circuit. I read somewhere that people have problems with the signals with LEDs and have to get different flasher/strobe module thingy. I haven't but I spliced anyway for the option. I've also read Department of Transport stuff and all it states is that the lights on the car must be red, white, or yellow. I'm sure there are technical specs somewhere but I can't find them, and the LEDs and HID headlights on my car are better than my truck, so I'm not worried. Bright like the sun!

[Digibeam]

Problem is we don't have Harbor Freight up in the Great White North...
So the alternative is Princess Auto.... They usually have flux capacitors on sale every Sunday.

[01Lambiero]

I recommend reverse polarity with a Harbor Freight flux capacitor.