Help with RGB LEDs - Page 2 - Electronic Circuits Projects Diagrams Free

Mike, K8LH · 8th June 2008, 01:07 PM

He (the OP) already referenced your site and this project in his first post...

Mike

gramo · 8th June 2008, 01:19 PM

O nice, i missed that link in the text

Mike, K8LH · 8th June 2008, 01:51 PM

Quote:

Originally Posted by futz

I'm putting up an article on my site now. It'll be ready in 10 or 15 minutes. Nothing terribly earth shaking. Just a simple little newb article.

Futz,

Nice demo, as always. My only 'nit' would be to use a shadow variable to prevent turning on the LEDs when they have a duty cycle of 0. Updating the output latch from the shadow also produces consistant duty cycle durations. Your example (and another forum members example) will produce different "on times" for the three colors when they have been set to the same duty cycle. Of course this is not important in the context/scope of your very nice demo.

Mike

Code:

;
;  Dim red, grn, blu As Byte    ' duty cycle, 0..255
;  Dim dcy As Byte              ' duty cycle counter, 0..255
;  Dim shadow As Byte           '
;
;  Interrupt rgb_interrupt()
;    t0if = 0                   ' clear timer0 interrupt flag
;    inc(dcy)                   ' increment duty cycle
;    if dcy = 0                 ' if new period
;      shadow = %01110000       ' set RC6..RC4 shadow bits
;    endif                      '
;    if red = dcy then          '
;      shadow.bit6 = 0          ' turn off RC6 shadow bit
;    endif                      '
;    if grn = dcy then          '
;      shadow.bit4 = 0          ' turn off RC4 shadow bit
;    endif                      '
;    if blu = dcy then          '
;      shadow.bit5 = 0          ' turn off RC5 shadow bit
;    endif                      ' 
;    LATC = shadow              ' update port from shadow
;  End Interrupt
;
rgb_interrupt                   ; 14 words
        bcf     INTCON,T0IF     ; clear timer 0 interrupt flag
        movlw   b'01110000'     ;
        infsnz  dcy,F           ; new period? no, skip, else
        movwf   shadow          ; set led bits in shadow
        movf    dcy,W           ; wreg = duty cycle, 0..255
        cpfsgt  red             ; (F) - (W), skip if (F) > (W)
        bcf     shadow,6        ; clear bit if (F) <= (W)
        cpfsgt  grn             ; grn - dcy, skip if grn > dcy
        bcf     shadow,4        ; clear bit if grn <= dcy
        cpfsgt  blu             ; blu - dcy, skip if blu > dcy
        bcf     shadow,5        ; clear bit if blu <= dcy
        movff   shadow,LATC     ; update port c from shadow
        retfie  FAST            ;

(1) this code / algorithm / method is public domain and anyone may use it as they wish...

futz · 8th June 2008, 04:22 PM

Quote:

Originally Posted by gramo

Its generally a very small difference in brightness, if noticeable at all with good LED's

Ya, the LED I'm using has very equal red and green. The blue is just a little dimmer. I plan to lower the value of the resistor feeding blue to equalize things a bit. Should un-pinkify the magenta a little.

futz · 8th June 2008, 04:32 PM

Quote:

Originally Posted by Mike, K8LH

My only 'nit' would be to use a shadow variable to prevent turning on the LEDs when they have a duty cycle of 0. Updating the output latch from the shadow also produces consistant duty cycle durations.

Good plan. I'll improve my quick and dirty code.

Quote:

Your example (and another forum members example) will produce different "on times" for the three colors when they have been set to the same duty cycle.

Only the tiniest bit different. But may as well fix it anyway with the shadow variable method.

Mike, K8LH · 8th June 2008, 05:30 PM

I apologize for picking 'nits'. No one could possibly perceive the timing difference. Also happy to contribute in a very small way to your very "shiny" site.

Please note that I reversed the bit polarity in my previous example but I'm sure you already figured that out.

Regards, Mike

futz · 8th June 2008, 05:43 PM

Quote:

Originally Posted by Mike, K8LH

I apologize for picking 'nits'. No one could possibly perceive the timing difference. Also happy to contribute in a very small way to your very "shiny" site.

Heh! Shiny! Ya, that's it.

No problem. I hadn't thought about that "nit". In some programs that could be a problem. But in mine it just wouldn't matter. Tis fixed anyway.

I have it cycling thru all 16.7milion colors now. Takes forever!

TiagoSilva · 8th June 2008, 05:54 PM

Quote:

Originally Posted by PwnToaster

Thanks again for your help. I believe the ATMega168 has internal pull down resistors, so an external resistor is not needed, but thanks for reminding me to enable them!

I gave a fast look at the datasheet and it only shows pull ups lol, it seems that you know everything, why do you ask for help then ?

(i'm in a bad mood today... sry)

PwnToaster · 8th June 2008, 06:26 PM

Quote:

Originally Posted by TiagoSilva

I gave a fast look at the datasheet and it only shows pull ups lol, it seems that you know everything, why do you ask for help then ?

(i'm in a bad mood today... sry)

I have a low budget and I don't want to buy anything that I don't have to, and I don't want to fry them.

I also like to figure everything out before I buy something so I can do it with minimal frustration. Here is my updated schematic. If you guys see anything, let me know! I can't thank you enough for all of your help everyone!

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Latest
LEDs	RayH	General Electronics Chat	33	12th June 2008 08:10 PM
180 leds!	justDIY	Electronic Projects Design/Ideas/Reviews	4	8th February 2007 05:46 PM
LEDs	zachtheterrible	Electronic Projects Design/Ideas/Reviews	25	5th October 2004 03:41 PM
RGB LEDs with PWM??	seahkw	Micro Controllers	2	27th August 2004 01:30 AM
LEDs-Super Bright White LEDs $1.35USD ea	ssullivan777	Datasheet/Parts Requests	0	27th February 2003 02:02 AM

8th June 2008, 01:07 PM	(permalink)
Mike, K8LH	He (the OP) already referenced your site and this project in his first post... Mike

8th June 2008, 01:19 PM	(permalink)
gramo	O nice, i missed that link in the text __________________ Spency. PIC Micro's - Your mind is the limit PIC's and interfacing with other devices - a PIC Basic Guide @ digital-diy.net

8th June 2008, 05:30 PM	(permalink)
Mike, K8LH	I apologize for picking 'nits'. No one could possibly perceive the timing difference. Also happy to contribute in a very small way to your very "shiny" site. Please note that I reversed the bit polarity in my previous example but I'm sure you already figured that out. Regards, Mike