all i need is the CMOS output will drive the PWM (with the capacitor making the fade)
then i use 4029 with 3 outputs (red green blue), the 4029 will make the 7 combinations needed for the rainbow colors. based on this

so it is self adjusting.
but i really need to be sure about the red wire ive marked.
how much voltage the 4029 will give to the capacitor ?
the capacitor MUST charge to 2/3 Vcc so the duty cycle raise to 100%.
could i use it without the three 10K resistors ?

 

You can safely eliminate R4, R5, and R6 in your scheme. You will find though, that selecting the right combination of RC is not so cut and dried. CMOS chips go rail to rail, they swing the full power supply voltage. This means that unless you select the timing just right, a full 2/3 of the time will be either too high or too low, with only 1/3 being in the linear area. Using another Schmitt trigger means it will always be in the linear region, and still turn completely off and completely on for brief periods of time.

My suggestion: build it and see. This is how I learned, I highly recommend it (and using a protoboard all the parts are reusable).

 

Thanks for the advice !

I've built it, and it works.
I have no scope, so i can't follow a lot of important information like wave forms and values...

i took off R4 R5 and R6,
R10 is 10k and C6 is 220uF
R8 pull up resistor is 1k - allows much brighter output.

my circuit now looks like this:

555 makes the clock for 4029 counter (about 1 pulse every 10s)
another 555 makes the PWM waveform (>500hz) for 3 comparators of LM339.
now the 4029 charges buffer\fade capacitor (C6=220uF), which is going into the comparator and set the duty cycle.
that way i have PWM controlled 3 channel (r,g,b) with fade in and out.
the 4029 is responsible for making the 7 combination of colors (r,g,b,r+g,r+b,g+b,r+g+b)


as to the linear 1/3 zone -
when i think of it - it is quite irrelevant:
the capacitor will go from 0v to Vcc, so it will go through the middle 1/3 range during 1/3 of the time,
which means i have a delay before a color fades and after a color fades.
but i can control the speed anyways with the 4029's 555 timer - problem solved.

i'm now waiting for my power RGB LEDs to arrive, and the MOSFETs !

 

Coolness. Enjoy!

 

Thanks,

you can follow this project on my blog: PWM RGB LED

the next part is the design of the lamp, and it will be surprising !

 

OK,

so my idea was to take the RGB LED control a bit further and use PWM for driving the LEDs.
that way the fade can be more accurate and linear.

I'm done with the electronics part, and next step is the housing and cooling of the LEDs module

please read more and watch pictures on my blog: RGB PWM LED control driver

Comments are welcomed