PIC PWM outputs? - Page 2 - Electronic Circuits Projects Diagrams Free

bananasiong · 28th November 2007, 06:01 PM

Can you post up your program? futz's program should work. Or you can first try the fixed duty cycle.

Andy1845c · 28th November 2007, 06:33 PM

Quote:

Originally Posted by bananasiong

Can you post up your program? futz's program should work. Or you can first try the fixed duty cycle.

Well, its pretty much exactly whats in the link Gayan posted

Code:

;=======pwm.ASM=================================15/11/06==
;     standard crystal 4.0MHz XT
;------------------------------------------------------------
;     configure programmer
 LIST P=16F628;f=inhx8m
 #include "P16F628.INC"  ; Include header file
 __CONFIG _PWRTE_ON  & _WDT_OFF & _HS_OSC & _BODEN_ON & _LVP_OFF & _CP_OFF & _MCLRE_OFF

; http://sandiding.tripod.com/Bertys.html
;------------------------------------------------------------
 cblock 0x20 ; Beginn General Purpose-Register
;-------------------------- counters 
 count1
 count2
 count3
;--------------------------
 endc
;--------------------------
#DEFINE pwmu PORTB,3
;--- Reset --------------------------------------------------
 org h'00'
 goto init  ; reset -> init
;--- Interrupt ----------------------------------------------
 org h'04'
;--------------------------
init clrf PORTA
 clrf PORTB
 movlw 0x07  ; Turn comparators off and enable pins for I/O 
 movwf CMCON 
 bcf STATUS,RP1
 call usi ; setari porturi
 call pause
 movlw 0xFF
 movwf PORTB
 call pause
 call set_timer
;-------------------------- asteapta puls de 1ms
uu 
 call pause
 movlw 0x02
 movwf CCPR1L
 call pause
 movlw 0x10
 movwf CCPR1L
 call pause
 movlw 0x40
 movwf CCPR1L
 call pause
 movlw 0x80
 movwf CCPR1L
 call pause
 movlw 0xFF
 movwf CCPR1L
 call pause
 movlw 0x80
 movwf CCPR1L
 call pause
 movlw 0x40
 movwf CCPR1L
 call pause
 movlw 0x10
 movwf CCPR1L
 goto uu
;~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
set_timer
 clrf T2CON
 clrf TMR2
 clrf INTCON
 bsf STATUS,RP0
 clrf PIE1
 bcf STATUS,RP0
 clrf PIR1
 bsf STATUS,RP0
 movlw 0xFF
 movwf PR2 ; compare with 255
 bcf STATUS,RP0
 movlw 0x02
 movwf CCPR1L
 movlw 0x03
 movwf T2CON ; prescaler 1:16 and postscaler 1:1
 movlw 0x3C
 movwf CCP1CON
 bsf T2CON,TMR2ON
 return
;************************************************************************
;       Subrutine de intarziere                                         *
;************************************************************************
pause movlw 0x02 ; 
 movwf count3
d3 movlw 0x3F
 movwf count1
d1 movlw 0xFA   
 movwf count2
d2 decfsz count2,F 
 goto d2  
 decfsz count1,F 
 goto d1  
 decfsz count3,F    
 goto d3          
 retlw 0x00
;============================================================
usi bsf STATUS,RP0 ; Bank 1
 movlw 0xFF ; all input
 movwf TRISA
 movlw 0x00
 movwf TRISB ; all output
 bcf STATUS,RP0 ; Bank 0
 return
;============================================================
 end

I just copied and pasted futz's as well. I assume both should output in RB3 and only RB3, correct?

jeremygaughan · 28th November 2007, 07:44 PM

I'm not sure how much of a difference this makes but your header says 16f628 and you said that you are using a 16f628a. I'll post an alternative code in a little while.

eng1 · 28th November 2007, 07:46 PM

Quote:

Originally Posted by Andy1845c

I just copied and pasted futz's as well. I assume both should output in RB3 and only RB3, correct?

Correct.

If you're using a PIC16F628A you have to make little changes: the list directive and the include file. I've played with futz's code and it's ok. I've chosen the internal oscillator. The original program requires a high speed crystal.

justDIY · 28th November 2007, 08:06 PM

Quote:

Originally Posted by Andy1845c

I have the LED on RB3. I have tried both ways, but RB3 should be sourcing power, right?

with pwm, it will alternately sink and source, so it doesn't matter on polarity, aside from your duty cycle will going one way or the other

jeremygaughan · 28th November 2007, 08:19 PM

Here's a code that you can put a led with a resistor on any of the PORTB bits. I put it on bit3 like you are already using. In the code there is a place that says
movlw 0x44
movwf runn
If you change this value the time it takes to fade changes. As is it fades out a few times a second. Something I noticed when writing this code is that leds do not light up in a linear fashion. You have to have an exponential increase in the PWM to get an even fade. This code if really long for what it does, but I hope it's easy to follow and does what you want. I also put a circuit that shows how to put the led. The short leg/the flat side is the - side.

Code:

;andy fade some lights


	list P=16f628a
#include <p16f628a.inc>
	__config _INTRC_OSC_NOCLKOUT & _BODEN_OFF & _WDT_OFF & _PWRTE_ON & _MCLRE_OFF & _CP_OFF & _CP_OFF 
	ERRORLEVEL -302
	
	cblock		20h
	BH,BL,wait,del_clk1,del_clk2,run,runn
	endc
	
	bsf	STATUS,RP0		;bank 1
	movlw	0x00
	movwf	TRISB		;make all outputs
	bcf	STATUS,RP0
	
	movlw	0x07		;turn off comparitors
	movwf	CMCON
	
	movlw	0x44			;adjustment for speed of fade
	movwf	runn
	
start
	call	firstt
	call	secondd
	call	thirdd
	call	fourthh
	call	fifthh
	call	sixthh
	call	seventhh
	call	eighthh
	call	ninthh
	call	tenthh
	call	ninthh
	call	eighthh
	call	seventhh
	call	sixthh
	call	fifthh
	call	fourthh
	call	thirdd
	call	secondd
	goto	start

firstt
	movf	runn,0
	movwf	run
first
	movlw	0xff
	movwf	PORTB		;turn on leds
	movlw	0x01		;set on time of duty cycle
	movwf	BH
loop
	decfsz	BH,1		;count down the on time
	goto	loop
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x01		;set off time of duty cycle
	movwf	BH
loop2
	incfsz	BH,1		;count up to the off time
	goto	loop2
	decfsz	run,1	;run the PWM for a moment
	goto	first
	return
	
secondd
	movf	runn,0
	movwf	run	
second
	movlw	0xff
	movwf	PORTB		;turn on leds
	movlw	0x03		;set on time of duty cycle
	movwf	BH
loopa
	decfsz	BH,1		;count down the on time
	goto	loopa
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x03		;set off time of duty cycle
	movwf	BH
loop2a
	incfsz	BH,1		;count up to the off time
	goto	loop2a
	decfsz	run,1	;run the PWM for a moment
	goto	second
	return


thirdd
	movf	runn,0
	movwf	run
third
	movlw	0xff
	movwf	PORTB		;turn on leds
	movlw	0x05		;set on time of duty cycle
	movwf	BH
loopb
	decfsz	BH,1		;count down the on time
	goto	loopb
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x05		;set off time of duty cycle
	movwf	BH
loop2b
	incfsz	BH,1		;count up to the off time
	goto	loop2b
	decfsz	run,1	;run the PWM for a moment
	goto	third
	return



fourthh
	movf	runn,0
	movwf	run
fourth
	movlw	0xff
	movwf	PORTB		;turn on leds
	movlw	0x07		;set on time of duty cycle
	movwf	BH
loopc
	decfsz	BH,1		;count down the on time
	goto	loopc
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x07		;set off time of duty cycle
	movwf	BH
loop2c
	incfsz	BH,1		;count up to the off time
	goto	loop2c
	decfsz	run,1	;run the PWM for a moment
	goto	fourth
	return

	
fifthh
	movf	runn,0
	movwf	run
fifth
	movlw	0xff
	movwf	PORTB		;turn on leds		
	movlw	0x09		;set on time of duty cycle
	movwf	BH

loopd
	decfsz	BH,1		;count down the on time
	goto	loopd
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x09		;set off time of duty cycle
	movwf	BH
loop2d
	incfsz	BH,1		;count up to the off time
	goto	loop2d
	decfsz	run,1	;run the PWM for a moment
	goto	fifth
	return


sixthh
	movf	runn,0
	movwf	run
sixth
	movlw	0xff
	movwf	PORTB		;turn on leds
	movlw	0x11		;set on time of duty cycle
	movwf	BH

loope
	decfsz	BH,1		;count down the on time
	goto	loope
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x11		;set off time of duty cycle
	movwf	BH
loop2e
	incfsz	BH,1		;count up to the off time
	goto	loop2e
	decfsz	run,1		;run the PWM for a moment
	goto	sixth
	return
	
	
seventhh
	movf	runn,0
	movwf	run
seventh
	movlw	0xff
	movwf	PORTB
	movlw	0x17		;set on time of duty cycle
	movwf	BH
loopf
	decfsz	BH,1		;count down the on time
	goto	loopf
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x17		;set off time of duty cycle
	movwf	BH
loop2f
	incfsz	BH,1		;count up to the off time
	goto	loop2f
	decfsz	run,1	;run the PWM for a moment
	goto	seventh
	return
	

eighthh
	movf	runn,0
	movwf	run
eighth
	movlw	0xff
	movwf	PORTB
	movlw	0x25		;set on time of duty cycle
	movwf	BH
loopg
	decfsz	BH,1		;count down the on time
	goto	loopg
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x25		;set off time of duty cycle
	movwf	BH
loop2g
	incfsz	BH,1		;count up to the off time
	goto	loop2g
	decfsz	run,1	;run the PWM for a moment
	goto	eighth	
	return
	
	
ninthh
	movf	runn,0
	movwf	run
ninth
	movlw	0xff
	movwf	PORTB
	movlw	0x35		;set on time of duty cycle
	movwf	BH
looph
	decfsz	BH,1		;count down the on time
	goto	looph
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x35		;set off time of duty cycle
	movwf	BH
loop2h
	incfsz	BH,1		;count up to the off time
	goto	loop2h
	decfsz	run,1	;run the PWM for a moment
	goto	ninth	
	return
	
	
tenthh
	movf	runn,0
	movwf	run
tenth
	movlw	0xff
	movwf	PORTB
	movlw	0x50		;set on time of duty cycle
	movwf	BH
loopi
	decfsz	BH,1		;count down the on time
	goto	loopi
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x50		;set off time of duty cycle
	movwf	BH
loop2i
	incfsz	BH,1		;count up to the off time
	goto	loop2i
	decfsz	run,1	;run the PWM for a moment
	goto	tenth
	return
	end

bananasiong · 29th November 2007, 12:49 AM

Hi,
Why isn't it working? Is the LED turned on? Have you seen anything on RB3 using oscilloscope?

Andy1845c · 29th November 2007, 04:18 AM

Quote:

Originally Posted by jeremygaughan

Here's a code that you can put a led with a resistor on any of the PORTB bits.

Hey, thanks for the code. It does work. It dosn't seem to fade down as far as I want to go, but i'll play with it.

What needs to be changed in order to use a 16F628 code on a 16F628A? I thought the two were interchagable to a point?

bananasiong, I never bothered putting the scope on RB3. I guess i could try it though.

Gayan Soyza · 29th November 2007, 04:35 AM

Hi andy whats your plan for smaller pics i'm using crude delay loops.working well.But the code gets bigger to do a smooth fade

BTW if you have problem with PIC's to do a PWM until you learn why not try with a simple opamp.

http://hw.metku.net/colorfade/index_eng.html

Pommie · 29th November 2007, 04:49 AM

Quote:

Originally Posted by Andy1845c

What needs to be changed in order to use a 16F628 code on a 16F628A? I thought the two were interchagable to a point?

The only difference, as far as I'm aware, is the config value. As long as you use the labels then it will either throw up an error or will work correctly. This is why I hate seeing hex values in config statements.

The line posted earlier be Jeremy has a slight mistake,

Code:

__config _INTRC_OSC_NOCLKOUT & _BODEN_OFF & _WDT_OFF & _PWRTE_ON & _MCLRE_OFF & _DATA_CP_OFF & _CP_OFF

I added the bit in red.

Also, the config above has both the internal oscillator and MCLR off. This is not recommended and you should probably turn MCLR on to prevent programming problems.

Mike.
Edit, I just noticed you posted the code above and your config is fine the way it is.

**3v0** · 29th November 2007, 12:02 PM

It is good to know assembler and the details of the hardware but maybe it is better to start with a high leve language like C.

For a person who does not know how to program the task of learning hardware + assembler + logic of the task at hand, may be too much.

If you find that the C code I posted earlier is understandable, I could provide a working example for the 18F1320 (Microchip C18 compiler).

jeremygaughan · 29th November 2007, 04:17 PM

Andy the code to fade the lights doesn't fade the PWM all the way down to zero but that would be easy to fix. Change the "duty cycle values" The closer to zero the darker it gets. Remember when you change them that the leds light up in an exponential fashion.

The header of the code I used was taken from another code. When I got errors from MPLAB I changed them until they stopped showing errors. (pretty scientific huh) I'm still learning about how to write code properly. Actually I wanted the internal oscillator turned on but I don't understand the data sheet so well. I tried to fix the header. Hopefully someone who knows will double check it. Really I don't know the secret to get the code from one pic to the other is. What I did was steal a header from a code that I know works and then I copied it into my code. In the rest of the code and circuit I use the datasheet to make sure the ports and bits are all assigned properly and wired correctly.

Here is a new code with two switches. They change the speed of the fade when you turn them on (close the switch). Also I put a revised circuit. I hope this helps.

Code:

;andy fade some lights


	list P=16f628a
#include <p16f628a.inc>
	__config _INTOSC_OSC_NOCLKOUT & _BODEN_OFF & _WDT_OFF & _PWRTE_ON & _MCLRE_ON & _DATA_CP_OFF & _CP_OFF 
	ERRORLEVEL -302
	
	cblock		20h
	BH,BL,wait,del_clk1,del_clk2,run,runn
	endc
	
	bsf	STATUS,RP0		;bank 1
	movlw	0x00
	movwf	TRISB		;make all PORTB outputs
	movlw	0xff
	movwf	TRISA		;make all PORTA inputs
	bcf	STATUS,RP0
	
	movlw	0x07		;turn off comparitors
	movwf	CMCON
	

	
start
	movlw	0x44			;adjustment for speed of fade
	movwf	runn
	btfss	PORTA,0			;call to see if low, if low make fade slower
	call	slower
	btfss	PORTA,1			;call to see if low, if low make fade faster

	call	faster	
	call	firstt
	call	secondd
	call	thirdd
	call	fourthh
	call	fifthh
	call	sixthh
	call	seventhh
	call	eighthh
	call	ninthh
	call	tenthh
	call	ninthh
	call	eighthh
	call	seventhh
	call	sixthh
	call	fifthh
	call	fourthh
	call	thirdd
	call	secondd
	goto	start

firstt
	movf	runn,0
	movwf	run
first
	movlw	0xff
	movwf	PORTB		;turn on leds
	movlw	0x01		;set on time of duty cycle
	movwf	BH
loop
	decfsz	BH,1		;count down the on time
	goto	loop
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x01		;set off time of duty cycle
	movwf	BH
loop2
	incfsz	BH,1		;count up to the off time
	goto	loop2
	decfsz	run,1	;run the PWM for a moment
	goto	first
	return
	
secondd
	movf	runn,0
	movwf	run	
second
	movlw	0xff
	movwf	PORTB		;turn on leds
	movlw	0x03		;set on time of duty cycle
	movwf	BH
loopa
	decfsz	BH,1		;count down the on time
	goto	loopa
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x03		;set off time of duty cycle
	movwf	BH
loop2a
	incfsz	BH,1		;count up to the off time
	goto	loop2a
	decfsz	run,1	;run the PWM for a moment
	goto	second
	return


thirdd
	movf	runn,0
	movwf	run
third
	movlw	0xff
	movwf	PORTB		;turn on leds
	movlw	0x05		;set on time of duty cycle
	movwf	BH
loopb
	decfsz	BH,1		;count down the on time
	goto	loopb
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x05		;set off time of duty cycle
	movwf	BH
loop2b
	incfsz	BH,1		;count up to the off time
	goto	loop2b
	decfsz	run,1	;run the PWM for a moment
	goto	third
	return


fourthh
	movf	runn,0
	movwf	run
fourth
	movlw	0xff
	movwf	PORTB		;turn on leds
	movlw	0x07		;set on time of duty cycle
	movwf	BH
loopc
	decfsz	BH,1		;count down the on time
	goto	loopc
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x07		;set off time of duty cycle
	movwf	BH
loop2c
	incfsz	BH,1		;count up to the off time
	goto	loop2c
	decfsz	run,1	;run the PWM for a moment
	goto	fourth
	return

	
fifthh
	movf	runn,0
	movwf	run
fifth
	movlw	0xff
	movwf	PORTB		;turn on leds		
	movlw	0x09		;set on time of duty cycle
	movwf	BH

loopd
	decfsz	BH,1		;count down the on time
	goto	loopd
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x09		;set off time of duty cycle
	movwf	BH
loop2d
	incfsz	BH,1		;count up to the off time
	goto	loop2d
	decfsz	run,1	;run the PWM for a moment
	goto	fifth
	return


sixthh
	movf	runn,0
	movwf	run
sixth
	movlw	0xff
	movwf	PORTB		;turn on leds
	movlw	0x11		;set on time of duty cycle
	movwf	BH

loope
	decfsz	BH,1		;count down the on time
	goto	loope
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x11		;set off time of duty cycle
	movwf	BH
loop2e
	incfsz	BH,1		;count up to the off time
	goto	loop2e
	decfsz	run,1		;run the PWM for a moment
	goto	sixth
	return
	
	
seventhh
	movf	runn,0
	movwf	run
seventh
	movlw	0xff
	movwf	PORTB
	movlw	0x17		;set on time of duty cycle
	movwf	BH
loopf
	decfsz	BH,1		;count down the on time
	goto	loopf
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x17		;set off time of duty cycle
	movwf	BH
loop2f
	incfsz	BH,1		;count up to the off time
	goto	loop2f
	decfsz	run,1	;run the PWM for a moment
	goto	seventh
	return
	

eighthh
	movf	runn,0
	movwf	run
eighth
	movlw	0xff
	movwf	PORTB
	movlw	0x25		;set on time of duty cycle
	movwf	BH
loopg
	decfsz	BH,1		;count down the on time
	goto	loopg
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x25		;set off time of duty cycle
	movwf	BH
loop2g
	incfsz	BH,1		;count up to the off time
	goto	loop2g
	decfsz	run,1	;run the PWM for a moment
	goto	eighth	
	return
	
	
ninthh
	movf	runn,0
	movwf	run
ninth
	movlw	0xff
	movwf	PORTB
	movlw	0x35		;set on time of duty cycle
	movwf	BH
looph
	decfsz	BH,1		;count down the on time
	goto	looph
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x35		;set off time of duty cycle
	movwf	BH
loop2h
	incfsz	BH,1		;count up to the off time
	goto	loop2h
	decfsz	run,1	;run the PWM for a moment
	goto	ninth	
	return
	
	
tenthh
	movf	runn,0
	movwf	run
tenth
	movlw	0xff
	movwf	PORTB
	movlw	0x50		;set on time of duty cycle
	movwf	BH
loopi
	decfsz	BH,1		;count down the on time
	goto	loopi
	movlw	0x00		;turn leds off
	movwf	PORTB
	movlw	0x50		;set off time of duty cycle
	movwf	BH
loop2i
	incfsz	BH,1		;count up to the off time
	goto	loop2i
	decfsz	run,1	;run the PWM for a moment
	goto	tenth
	return
	
slower
	movlw	0x88		;puts higher value in speed adjustment
	movwf	runn
	return
faster
	movlw	0x11		;puts lower value in speed adjustment
	movwf	runn
	return
	
	end

futz · 29th November 2007, 04:42 PM

Quote:

Originally Posted by 3v0

It is good to know assembler and the details of the hardware but maybe it is better to start with a high leve language like C.

For a person who does not know how to program the task of learning hardware + assembler + logic of the task at hand, may be too much.

I very much disagree. That might be somewhat true with PC's, but when you're doing microcontrollers and the associated electronics you absolutely MUST know what's going on with the hardware, in detail. I believe that assembler should be the first language you learn, starting simple and working up to more complex things.

Once you've got a handle on that, only then should you start using higher level languages (if you even want to at that point).

I believe higher level languages tend to insulate you from the details somewhat, making understanding more difficult, especially for newbs.

Not only that, but they make porky, fat code that eats up memory and runs slow.

**3v0** · 29th November 2007, 06:50 PM

Quote:

Originally Posted by futz

I believe higher level languages tend to insulate you from the details somewhat, making understanding more difficult, especially for newbs.

You do not need to know much hardware detail to blink a LED, or even to do PWM. I makes understanding/learning easier......

In a more perfect world preople would learn a high level language first on a PC. Ater that we could have them learn assembly and processor details. But programing on the PC has lost the luster that programming uC's still have. You have to start where the interest is and currently that is uC's.

Start them with a high level language. Let them get good at blinking LEDs and such. You hold their hand, hide the details, and they get hooked. Over time you introduce more complex hardware and how it work.

At this point you can teach assembler. You teach assembler not because it is the worlds greatest programming language. You teach it because it is the best way to expose them to the nuts and bolts that you have been hidding.

The fact that compiled code takes more memory is not a big concern here. The inexpensive 18F family has memory to spare for learning.

**Nigel Goodwin** · 29th November 2007, 07:10 PM

Quote:

Originally Posted by 3v0

You do not need to know much hardware detail to blink a LED, or even to do PWM. I makes understanding/learning easier......

I would disagree, assembler forces understanding of the hardware on you, a high level language hides it from you - unless the compiler has specific commands for implementing hardware PWM you essentially copy the way you do it in assembler, and it's MUCH easier to implement if you have an understanding of assembler.

Do learning assembler first, you then have the hardware understanding required if you move to a high level language.

Where this advantage is starting to blur is the 18F series, simply because there's a free compiler available, and the application notes are mainly provided written in C. So in that case, I would suggest learning a little assembler on a 16F (so you understand PIC hardware), and probably go directly to C on the 18F.

Incidently, in Universities in the past you weren't allowed to use high level languages until you had mastered machine code, never mind assembler!

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28th November 2007, 06:01 PM	(permalink)
bananasiong	Can you post up your program? futz's program should work. Or you can first try the fixed duty cycle. __________________ Superman returns..

28th November 2007, 07:44 PM	(permalink)
jeremygaughan	I'm not sure how much of a difference this makes but your header says 16f628 and you said that you are using a 16f628a. I'll post an alternative code in a little while. __________________ jeremy

29th November 2007, 12:49 AM	(permalink)
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29th November 2007, 04:35 AM	(permalink)
Gayan Soyza	Hi andy whats your plan for smaller pics i'm using crude delay loops.working well.But the code gets bigger to do a smooth fade BTW if you have problem with PIC's to do a PWM until you learn why not try with a simple opamp. http://hw.metku.net/colorfade/index_eng.html __________________ Gayan My Website http://gsmicro.blogspot.com/

29th November 2007, 12:02 PM	(permalink)
3v0	An observation. It is good to know assembler and the details of the hardware but maybe it is better to start with a high leve language like C. For a person who does not know how to program the task of learning hardware + assembler + logic of the task at hand, may be too much. If you find that the C code I posted earlier is understandable, I could provide a working example for the 18F1320 (Microchip C18 compiler).