Roof LEDs again

[jrz126]

As some of you know, I have 62 blue leds mounted in the headliner of my car, and they look rather nice.
**broken link removed** (I was playing around with a fog machine for that picture)

Now the tranny is starting to slip, a wheel bearing went bad, rust bubbles on the fender... So I'm considering getting a new car. Only thing thats keeping me from doing so is all of the work that I have put into this car.

I'm actually considering redoing the LEDs and using some of those RGB leds to get multiple colors. It would be amazing to have them fade from a nice deep blue to orange to purple to green to...

Now for the point of this thread...
How exactly are those controlled to achieve any color possible? And are there any of these leds that have this multi-color ability with fewer than 4 legs? If I do decide to do this, I dont want to end up with atleast 187 wires (62 leds * 3 colors +1 common power wire).

I know I'm crazy...

 

[Optikon]

As some of you know, I have 62 blue leds mounted in the headliner of my car, and they look rather nice.
**broken link removed** (I was playing around with a fog machine for that picture)

Now the tranny is starting to slip, a wheel bearing went bad, rust bubbles on the fender... So I'm considering getting a new car. Only thing thats keeping me from doing so is all of the work that I have put into this car.

I'm actually considering redoing the LEDs and using some of those RGB leds to get multiple colors. It would be amazing to have them fade from a nice deep blue to orange to purple to green to...

Now for the point of this thread...
How exactly are those controlled to achieve any color possible? And are there any of these leds that have this multi-color ability with fewer than 4 legs? If I do decide to do this, I dont want to end up with atleast 187 wires (62 leds * 3 colors +1 common power wire).

I know I'm crazy...

The RGB types are just three LEDS in one package as I understand it.. So to get the various colors, you just need to run them with various current ratio's.

For example: Lets say 100% current is 10mA

100% Red + 100% blue + 0% green = Intense purple
50% Red + 50% blue + 0% green = less intense purple

0% Red + 100% blue + 100% green = Intense aqua
0% red + 100% blue + 50% green = intense deeper aqua
0% red + 50% blue + 25% green = less intense deeper aqua (same color ratio)

so you can see, by keeping the ratio's but scaling you can adjust the intensity and the base color is formed by the ratio's of all three colors.

 

[Exo]

Like opticon says, these are 3 color leds in one package.
They control each of the 3 colors with PWM, this allows you to change the brigtness of each color.

Then it's just upto mixing colors. PWM is much simpler then current control because a µC can do that and this allows some automatic sequences.

 

[Oznog]

They don't have them in less than 4-lead pkgs.

Now normally if we had a bunch of 2.7v red LEDs for example and 12v, we might put 3 or 4 in series with a single ballast resistor. This cannot be done with tricolors because they share a common anode or cathode for all the colors, so all the LEDs must be in parallel. If you use discrete R, G, and B LEDs each in their own strings you won't have this problem, but the color blending will not look as awesome. You'll see a red and blue LED up close, only from a ways off will it appear purple.

 

[jrz126]

Ok, I thought they were controlled by PWM. I'm going to need alot of microcontrollers to control 62 of them. Or is there a better way?
As far as the serial/parallel goes, I was already planning on running them all in parallel so I could have control over each and every LED.

oh and where is the best place to purchase these from? Are there any manufacturers that give free samples?

 

[Optikon]

Ok, I thought they were controlled by PWM. I'm going to need alot of microcontrollers to control 62 of them. Or is there a better way?
As far as the serial/parallel goes, I was already planning on running them all in parallel so I could have control over each and every LED.

oh and where is the best place to purchase these from? Are there any manufacturers that give free samples?

Check fairchild semiconductor... I think they make them and I'm sure they offer free samples.

Also for control, if you want low cost a PIC is good option BUT, you dont get alot of I/O.. Consider a CPLD device if you dont mind writing a little VHDL for the PWM control. It is very easy and you can find lots of help and reference designs.. Also the software tools are FREE and the devcies themselves can be had for a few dollars.. AND you only need one because you can get them with 100's of I/O pins for all those PWM signals.. 62 of them is no issue at all.

 

[Oznog]

Ok, I thought they were controlled by PWM. I'm going to need alot of microcontrollers to control 62 of them. Or is there a better way?
As far as the serial/parallel goes, I was already planning on running them all in parallel so I could have control over each and every LED.

If this was in response to me, there is some confusion. You can still use one transistor and drive any number of red LEDs, another any number of blue LEDs, etc. Not being able to put them is series affects the way you wire it, requires many more resistors, and it will not be as efficient. But none of these are killer problems.

If all the LEDs turn the same color at once you only need 3 PWM channels. If you want different LEDs to turn different colors independently you will need more pins. PIC only has 2 hardware PWMs but you can usually fake it out just turning on and off other pins with good results.
On a 40 pin device there will be over 30 pins available. It varies on the part and configuration.

 

[Mike - K8LH]

Oznog is right... Just three PWM outputs should do it... Then use a hefty power supply and drivers...

Regards, Mike

 

[Oznog]

What is it, National Resurrect-A-Dead-Thread Day?