PWM Smoothing Coding Problem

[Suraj143]

Hi! I’m working with a simple delay loop that can generate a PWM part (without a PWM module).

My target is to fade a LED smoothly.

I have a pair of tested values. By loading one of these values & call Main routine it will show the LED dim or full brightness.

What I need is to change DIM values to BRIGHT values nicely (linear) to make the LED fade.

Any method greatly appreciated.

Thanks

LED is very DIM by loading these values

;DIM		movlw	.255
;		movwf	SaveONtime
;		movlw	.1
;		movwf	saveONcount
;		movlw	.1
;		movwf	SaveOFFtime
;		movlw	.40
;		movwf	saveOFFcount


LED is fully BRIGHT by loading these values

;BRIGHT	movlw	.1
;		movwf	SaveONtime
;		movlw	.40
;		movwf	saveONcount
;		movlw	.255
;		movwf	SaveOFFtime
;		movlw	.1
;		movwf	saveOFFcount


Main		call	ON
		call	OFF
		goto	 Main


ON		movlw	0xff		;turn on leds
		movwf	PORTB			
		movf	SaveONtime,W		
		movwf	ONtime
		movf	saveONcount,W
		movwf	ONcount						
loopON		incfsz	ONtime,F	;count up the on time
		goto	loopON
		decfsz	ONcount,F
		goto	$-3
		return


OFF		movlw	0x00		;turn off leds
		movwf	PORTB			
		movf	SaveOFFtime,W			
		movwf	OFFtime
		movf	saveOFFcount,W
		movwf	OFFcount						
loopOFF		incfsz	OFFtime,F	;count up the off time
		goto	loopOFF
		decfsz	OFFcount,F
		goto	$-3
		return

 

[geko]

Try something like this. Timer 2 is good for generating the interrupt which takes care of the PWM. Then gradually change the value of ledPwm variable from 0x00 (led off) to 0xFF (led 100% on) to fade the LED.

                ; define variables
                ;
                cblock 0x20
                                ledPwm          ; LED PWM value
                                pwmCntr         ; PWM 'ramp' counter
                                pwmWkg          ; working variable
                endc
 
 
                ; call this from a timer driven interrupt 
                ; every 40uS for 98Hz refresh.
 
_pwm            incfsz          pwmCntr,F       
                goto            _noRollover
_resetPWM       incf            pwmCntr,F
                movfw           ledPwm          
                movwf           pwmWkg
                incfsz          pwmWkg,W
                bcf             PORTA, LED
_noRollover     incf            pwmWkg,f        
                skpnz
                bsf             PORTA, LED
 
                ; exit ISR here
                ; ---------------------------------------
 
 
_loop           ; software fade delay code here
                incf            ledPwm,F
                incfsz          ledPwm,W
                goto            _loop
                ; stop when ledPWM == 0xFF

 

[Suraj143]

Thanks geko I'll try your coding I'm working hard with my coding to get a smooth fade but I couldn't.

Now I'll check with your one.

Thanks for the help.

 

[wschroeder]

Maybe this is smooth enough?

https://www.youtube.com/watch?v=isftM5mUqRU

And this is multi-smooth:

https://www.youtube.com/watch?v=aeHFavqIe7U

 

[Suraj143]

Maybe this is smooth enough?

https://www.youtube.com/watch?v=isftM5mUqRU

And this is multi-smooth:

https://www.youtube.com/watch?v=aeHFavqIe7U

Yes my friend that smooth is good.I'm doing from assembly language.Is that your circuit?
Do you have any coding ideas to share?

 

[wschroeder]

Most of the code here:
https://www.mikroe.com/forum/viewtopic.php?t=10513
https://www.mikroe.com/forum/viewtopic.php?t=11194