Problem with 16F628A and sevo

sparky72 · Feb 5, 2011

Recently I put this simple program together to move an s3003 Futaba servo approximately 180 degrees clockwise and back 180 degrees counterclockwise with one push of a momentary switch. I am using the MCLRE pin to reset program when needed. The program does as I expect but the way that I have it is that I cannot get out of the counterclockwise programming to a sleep instruction without screwing up the counterclockwise section of the program. My experience is very limited in programming so I thought I would post this for a little help which would be appreciated very much. Thanks in advance for any help that I may receive. I have attached the source code.

Code:

[ATTACH]50650[/ATTACH]

House0Fwax · Feb 5, 2011

The way you have it, you'll never get out of the loop.

Code:

Backward    	
		bsf		PORTB,2				
		call		Delay2			;Delay for 1ms (counterclockwise motion)
		bcf		PORTB,2
	    goto		Backward

How about doing it similar to how you have 'Forward'

Code:

		movlw		d'25'
	    movwf		Count

Forward
		bsf			PORTB,2
		call		Delay3			;delay for 2ms "clockwise motion"
		bcf	    	PORTB,2
		call		Delay1
		call		Delay1
		call		Delay1			;delay for 18ms
		decfsz		Count
		goto		Forward

sparky72 · Feb 5, 2011

House0Fwax said:

The way you have it, you'll never get out of the loop.

Code:

Backward    	
		bsf		PORTB,2				
		call		Delay2			;Delay for 1ms (counterclockwise motion)
		bcf		PORTB,2
	    goto		Backward

How about doing it similar to how you have 'Forward'

Code:

		movlw		d'25'
	    movwf		Count

Forward
		bsf			PORTB,2
		call		Delay3			;delay for 2ms "clockwise motion"
		bcf	    	PORTB,2
		call		Delay1
		call		Delay1
		call		Delay1			;delay for 18ms
		decfsz		Count
		goto		Forward

Thanks House of Wax for the quick response. I have tried what you suggested but when I do that, It just moves counterclockwise
90 degrees, and I need to go back approx.180 degrees

House0Fwax · Feb 5, 2011

If the following code (what I meant in my earlier post) turns the servo 90 degrees;

Code:

;Turn180 Backwards		
		movlw		d'25'
	        movwf		Count		

Backward    	
		bsf			PORTB,2				
		call		Delay2			;Delay for 1ms (counterclockwise motion)
		bcf			PORTB,2
		decfsz		Count
	    goto		Backward

and you want 180, then how about movlw d'50' instead?
I don't have a servo that works, so I can't try it out myself.

sparky72 · Feb 5, 2011

House0Fwax said:
If the following code (what I meant in my earlier post) turns the servo 90 degrees;

Code:

;Turn180 Backwards movlw d'25' movwf Count Backward bsf PORTB,2 call Delay2 ;Delay for 1ms (counterclockwise motion) bcf PORTB,2 decfsz Count goto Backward

and you want 180, then how about movlw d'50' instead?
I don't have a servo that works, so I can't try it out myself.

Thanks again HouseOFwax. Your latest suggestion helped somewhat. On the backward movement it slows down quite a bit towards the end but is very close to the amount of travel that I need. At least we seem to be on the right track now. I will tweak the count figures a bit and let you know how I make out. I have to leave this project for the time being but will get back to it probably tomorrow. Take care

sparky72 · Feb 7, 2011

HouseOFwax, after fooling around with the figures a bit as you suggested, I finally have it working suitable for my application. I left the Count for the forward movement figure at 25 and used 55 for the Count figure for the backward motion. This is just a hobby for me, as a retiree and I have learned a lot from people like you and others who are willing to spend their time and share their knowledge with me and others. Thanks again

House0Fwax · Feb 8, 2011

After my last post I was chatting to a friend in the pub, he happened to have a spare servo (microscopic thing) that he has donated to me. I tried your code with it and it 'twitched' a bit.
I have since had a go at it myself.

Code:

	    LIST	        p=16f628A
	    include			"p16f628A.inc"
	    __CONFIG	_CP_OFF & _DATA_CP_OFF &_LVP_OFF & _BOREN_OFF &_MCLRE_OFF & _WDT_OFF & _PWRTE_ON & _INTOSC_OSC_NOCLKOUT		
	    
	    
	    ERRORLEVEL -302

 
		cblock	0x20
				d0
				d1
				d2
				count
				endc
			
				
			
			
		ORG			0x0000
		
		movlw		0x07		    ;like 16f84
		movwf		CMCON
		


Initialization

		banksel		TRISB			;select bank 1
		movlw		b'00000000'		
		movwf		TRISB			;Make TRISB all outputs 
		movwf		TRISA			;Make TRISA all outputs
		banksel		PORTB			;Select Bank 0			
		
		clrf		PORTA
		clrf		PORTB
		

Start
;--------------------------------------------------------------------
		movlw	0x64
		Movwf	Count			;allow travel time and hold
Zero		
		bsf			PORTB,2		
		call		Delay1.25	;Pulse on for 1.25mS, 0 position
		bcf	    	PORTB,2		
		call		Delay20		;Pause for 20mS (servo's expect it)
		decfsz 		count
		goto		Zero


		movlw	0x64
		Movwf	Count			;allow travel time and hold
Ninety
		bsf			PORTB,2
		call		Delay1.5	;Pulse on for 1.5mS, 90 position
		bcf	    	PORTB,2
		call		Delay20		;Pause for 20mS (servo's expect it)
		decfsz 		count
		goto		Ninety
		
		movlw	0x64
		Movwf	Count			;allow travel time and hold
One_eighty		
		bsf			PORTB,2
		call		Delay1.75	;Pulse on for 1.75mS, 180 position
		bcf	    	PORTB,2
		call		Delay20		;Pause for 20mS (servo's expect it)
		decfsz 		count
		goto		One_eighty

		goto	Start
;--------------------------------------------------------------------
Delay1.5				;0.0015 seconds
		movlw 0xF1
		movwf d0
		movlw 0x02
		movwf d1
loop1.5
		decfsz d0, f
		goto loop1.5
		decfsz d1, f
		goto loop1.5

; Rest = 2 Cycles
		goto  $+1
		
		RETLW	0x00
;---------------------		
Delay20					;0.02 seconds
		movlw 0xF8
		movwf d0
		movlw 0x1A
		movwf d1
loop20
		decfsz d0, f
		goto loop20
		decfsz d1, f
		goto loop20

; Rest = 1 Cycles
		nop
		RETLW	0x00
;---------------------	
Delay1.25				;0.00125 seconds
		movlw 0x9E
		movwf d0
		movlw 0x02
		movwf d1
loop1.25
		decfsz d0, f
		goto loop1.25
		decfsz d1, f
		goto loop1.25

; Rest = 1 Cycles
		nop
		RETLW	0x00
	
;---------------------	
Delay1.75				;0.00175 seconds
		movlw 0x44
		movwf d0
		movlw 0x03
		movwf d1
loop1.75
		decfsz d0, f
		goto loop1.75
		decfsz d1, f
		goto loop1.75

; Rest = 1 Cycles
		nop
		RETLW	0x00
	
;-----------------------------------------------
		
    	END

Having looked at this site
and using their suggested timings of 1.25mS and 1.75mS I found that my servo only moved a fraction off centre in each direction. I have since 'played' with the timings and have managed to get very nearly 0 - 180 using timings of 0.5mS and 2.3mS.

The above code drives the same port pin as your original code (since it was based on it).
Have a go, see what you think.

sparky72 · Feb 8, 2011

HouseOFwax, I tried the above code without changing the delays and I got the same results you had. The servo just twitches. I changed the delay routines as per your suggestion and the servo just moves to the forward position and stays there. I also tried it without going to the 90 degree delay but still to no avail. I guess I will just stay with the code that we came up with last week as it seems to work ok for the application I am using it with. Thanks again for all the trouble you went to, to help me out. It has been a good learning experience for me.

House0Fwax · Feb 8, 2011

You are very welcome to the help, (I've enjoyed it). I have never had the chance to play with a working servo until very late Sunday night (after drinking). It seems that the 1.5mS sets things to 90 degrees 'as a rule' however different types of servos have different limits. The one I have has no markings that I can see. As such, it's just a case of trial and error.

Best wishes.

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