Post by thread:HELP! R/C Servo Code problems-Can U find problem.

I am a beginner and I'll bet one of you servo experts can solve my problem in about 5 seconds. Undoubtedly I have made a code error. I am trying to control the position of a R/C servo using a Pot. I am timing the discharge of a capacitor to determine the pot position. I ran that part of the program by itself and displayed the results of pot position in binary on port b, everything worked fine. The leds displayed position from 1-255 (limit=255). When I combined the pot program with a servo program nothing happens. On power up the servo moves immediately to one position and does not respond to the pot position. If I ground PIC 16f84 pot position pin nothing happens unless I reset power where it will stay in a middle position. If I apply 5 volts nothing happens until a power reset. BO I have attached the code, if someone could review and comment I would be able to get on with my life. Thankyou Jon ;*******************************; ; MAIN ENTRY POINT ; ;*******************************; ORG 0X000 GOTO START ;*******************************; ; INTERRUPT SERVICE CODE ; ;*******************************; ORG 0X004 RETFIE ;return from interrupt ;*******************************; ; SETUP PORTS Etc. ; ;*******************************; START MOVLW B'10000111' OPTION ;set up the OPTION register MOVLW B'00000000' MOVWF 0BH ;Set up the INTCON register MOVLW B'00000000' TRIS PORTA ;setup port A BITs 0-3 as OUTPUT MOVWF PORTA ;clear port A MOVLW B'11111111' TRIS PORTB ;setup port B BITs 0-7 as INPUT ; MOVLW 080H ;Setup SERVOS to CENTRE ; MOVWF PULSE1S ;Servo 1 Initial Position ; MOVWF PULSE2S ;Servo 2 Initial Position ; MOVLW 040H ; MOVWF PULSE1PS1 ; MOVWF PULSE2PS1 ; MOVLW 0C0H ; MOVWF PULSE1PS2 ; MOVWF PULSE2PS2 ;*******************************; ; MAIN LOOP ; ;*******************************; ; FIRST SERVO ; ;*******************************; BEGIN MOVFW PULSE1S ;LOAD Pulse Store MOVWF PULSE1 ;LOAD Pulse Counter MOVLW 0FAH ;Load 1ms. counter MOVWF DELAY1 ;Get it into reg BSF PORTA,0 ;Start pulse output HIMS1 NOP ;Force loop into 4 cycle duty (even #) DECFSZ DELAY1,F ;Decriment Counter DELAY1 GOTO HIMS1 ;No yet Zero -> Goto HIMS1 HIGH1 NOP ;Force loop into 4 cycle duty (even #) DECFSZ PULSE1,F ;Decriment PULSE1 GOTO HIGH1 ;Not Yet Zero -> Gotot HIGH1 BCF PORTA,0 ;End pulse output ;***********************************; ; EXTEND TO FULL 2 mSEC PULSE WIDTH ; ;***********************************; MOVFW PULSE1S ;get the register position value SUBLW 0FAH ;subtract it from 250 MOVWF PULSE1 ;place the difference in the counter LOW1 NOP ;force loop into 4 cycle duty (even #) DECFSZ PULSE1,F ;loop for high part of duty cycle GOTO LOW1 ;while pulse > 0 ;***********************************; ; READ INPUT POT B0 ; ;***********************************; UP_DOWN CLRF PULSE1S ;Clear previous value MOVLW B'11111110' ;setup port B BITs as OUTPUT TRIS PORTB ; BSF PORTB,0 ;START CAPACITOR CHARGE NOP ;Time to charge NOP ;Time to charge NOP ;Time to charge NOP ;Time to charge NOP ;Time to charge NOP ;Time to charge NOP ;Time to charge NOP ;Time to charge NOP ;Time to charge NOP ;Time to charge MOVLW b'11111111' ;Set PortB,0 to input TRIS PORTB ;Teach portA MEAS1 CLRWDT BTFSS PORTB,0 ;Test b0 skip if 1 GOTO UP_DOWN INCFSZ PULSE1S,F ;Inc pulse1s skip if 0 GOTO MEAS1 ; CLEANUP MOVLW 0XFF MOVF PULSE1S,W ;***********************************; ; DUTY CYCLE DELAY LOOP 15 mSEC ; ;***********************************; LOOP15 MOVLW 0FH ;load the value of 15 MOVWF DELAY2 ;store it in counter Delay2 DUTY1 MOVLW 0FAh ;load the value of 250 MOVWF DELAY1 ;Store it int the counter delay1 DUTY2 NOP ;force loop into 4 cycle duty (even #) DECFSZ DELAY1,F ;Decriment Delay1 GOTO DUTY2 ;if not zero -> Goto DUTY2 DECFSZ DELAY2,F ;Decriment Delay2 GOTO DUTY1 ;if not zero -> Goto DUTY1 FINAL GOTO BEGIN ;restart the MAIN Programme loop ; ERROR_ SLEEP ;Hmm if we got here we ha END ;The End

I am a beginner and I'll bet one of you servo experts can solve my problem in about 5 seconds. Undoubtedly I have made a code error. I am trying to control the position of a R/C servo using a Pot. I am timing the discharge of a capacitor to determine the pot position. I ran that part of the program by itself and displayed the results of pot position in binary on port b, everything worked fine. The leds displayed position from 1-255 (limit=255). When I combined the pot program with a servo program nothing happens. On power up the servo moves immediately to one position and does not respond to the pot position. If I ground PIC 16f84 pot position pin nothing happens unless I reset power where it will stay in a middle position. If I apply 5 volts nothing happens until a power reset, it may move to one extreme. At no time does the servo respond to pot position. With power cycle servo will go from a center position to one extreme, but never to the other. BO is used to measure the pot and A0 is used to control the servo. I switch B0 from output to input to measure cap discharge. I have attached the code, if someone could review and comment I would be able to get on with my life. Thankyou Jon ;*******************************; ; MAIN ENTRY POINT ; ;*******************************; ORG 0X000 GOTO START ;*******************************; ; INTERRUPT SERVICE CODE ; ;*******************************; ORG 0X004 RETFIE ;return from interrupt ;*******************************; ; SETUP PORTS Etc. ; ;*******************************; START MOVLW B'10000111' OPTION ;set up the OPTION register MOVLW B'00000000' MOVWF 0BH ;Set up the INTCON register MOVLW B'00000000' TRIS PORTA ;setup port A BITs 0-3 as OUTPUT MOVWF PORTA ;clear port A MOVLW B'11111111' TRIS PORTB ;setup port B BITs 0-7 as INPUT MOVLW 080H ;Setup SERVOS to CENTRE; MOVWF PULSE1S ;Servo 1 Initial Position ; MOVWF PULSE2S ;Servo 2 Initial Position ; MOVLW 040H ; MOVWF PULSE1PS1 ; MOVWF PULSE2PS1 ; MOVLW 0C0H ; MOVWF PULSE1PS2 ; MOVWF PULSE2PS2 ;*******************************; ; MAIN LOOP ; ;*******************************; ; FIRST SERVO ; ;*******************************; BEGIN MOVFW PULSE1S ;LOAD Pulse Store MOVWF PULSE1 ;LOAD Pulse Counter MOVLW 0FAH ;Load 1ms. counter MOVWF DELAY1 ;Get it into reg BSF PORTA,0 ;Start pulse output HIMS1 NOP ;Force loop into 4 cycle duty (even #) DECFSZ DELAY1,F ;Decriment Counter DELAY1 GOTO HIMS1 ;No yet Zero -> Goto HIMS1 HIGH1 NOP ;Force loop into 4 cycle duty (even #) DECFSZ PULSE1,F ;Decriment PULSE1 GOTO HIGH1 ;Not Yet Zero -> Gotot HIGH1 BCF PORTA,0 ;End pulse output ;***********************************; ; EXTEND TO FULL 2 mSEC PULSE WIDTH ; ;***********************************; MOVFW PULSE1S ;get the register position value SUBLW 0FAH ;subtract it from 250 MOVWF PULSE1 ;place the difference in the counter LOW1 NOP ;force loop into 4 cycle duty (even #) DECFSZ PULSE1,F ;loop for high part of duty cycle GOTO LOW1 ;while pulse > 0 ;***********************************; ; READ INPUT POT B0 ; ;***********************************; UP_DOWN CLRF PULSE1S ;Clear previous value MOVLW B'11111110' ;setup port B BITs as OUTPUT TRIS PORTB ; BSF PORTB,0 ;START CAPACITOR CHARGE NOP ;Time to charge NOP ;Time to charge NOP ;Time to charge NOP ;Time to charge NOP ;Time to charge NOP ;Time to charge NOP ;Time to charge NOP ;Time to charge NOP ;Time to charge NOP ;Time to charge MOVLW b'11111111' ;Set PortB,0 to input TRIS PORTB ;Teach portA MEAS1 CLRWDT BTFSS PORTB,0 ;Test b0 skip if 1 GOTO UP_DOWN INCFSZ PULSE1S,F ;Inc pulse1s skip if 0 GOTO MEAS1 ; CLEANUP MOVLW 0XFF MOVF PULSE1S,W ;***********************************; ; DUTY CYCLE DELAY LOOP 15 mSEC ; ;***********************************; LOOP15 MOVLW 0FH ;load the value of 15 MOVWF DELAY2 ;store it in counter Delay2 DUTY1 MOVLW 0FAh ;load the value of 250 MOVWF DELAY1 ;Store it int the counter delay1 DUTY2 NOP ;force loop into 4 cycle duty (even #) DECFSZ DELAY1,F ;Decriment Delay1 GOTO DUTY2 ;if not zero -> Goto DUTY2 DECFSZ DELAY2,F ;Decriment Delay2 GOTO DUTY1 ;if not zero -> Goto DUTY1 FINAL GOTO BEGIN ;restart the MAIN Programme loop ; ERROR_ SLEEP ;Hmm if we got here we ha END ;The End

On Sat, 10 Jan 1998 11:34:40 EST PHXSYS <spam_OUTPHXSYSTakeThisOuTAOL.COM> writes: >I am trying to control the position of a R/C servo using a Pot. I am >timing >the discharge of a capacitor to determine the pot position. [...] > MEAS1 CLRWDT > BTFSS PORTB,0 ;Test b0 skip if 1 > GOTO UP_DOWN > INCFSZ PULSE1S,F ;Inc pulse1s skip if 0 > GOTO MEAS1 ; >CLEANUP MOVLW 0XFF > MOVF PULSE1S,W As written, there is no way out of the measurement routine except when PULSE1S overflows to 0. You don't ever want to go back to UP_DOWN (taking a new measurement) except as part of the main loop after doing a servo pulse with the old measurement. Rewrite it to something like: meas_lp btfss PORT_B,0 ;When cap has discharged, goto meas_done ;measurement done. incfsz PULSE1S,f ;Inc. measured value goto meas_lp ;If no overflow, wait more decf PULSE1S,f ;Fix overflow value back to 255 meas_done The "cleanup", whatever it's supposed to do, appears unnecessary. Make sure the WDT prescaler is set high enough to guarantee that the WDT won't run out during the 20 ms main loop. Then clear it just at the start of each main loop. It would help to write the delay, cap measure, etc. sections as subroutines. This makes it easier to follow the flow through the main loop as well as expand the function of the program later.

Just out of interest the servo control pulse never goes below about 0.9mS so measuring this part of the input is a waste of resolution if you want to keep to 8 bits. What I do is have fixed delay of about 875uS and then I start measuring the input pulse, this gives me 5uS resolution and a count of FF is about 2.035mS. In the output routine I have the same fixed delay before I start the variable part. You must keep the steps as small as possible if you go up to 10uS resolution the servos will jitter and buzz. If anyone wants my basic input and output routines email me and I will send them out to you. Ken. +-----------------------------+--------------------------------------+ | Ken Hewitt G8PWC | Email .....kenKILLspam@spam@welwyn.demon.co.uk | | /\/\/\/\/\/\/\/\/ | Homepage http://www.welwyn.demon.co.uk | +-----------------------------+--------------------------------------+

I've also played around with RC pulse a fair bit and the system I use uses the TMR0 function of a 4Mhz part to time and generate RC pulses. If you use it with the pre-scaler set to divide by 8 then you end up with 125 ticks being a millisecond. Using 1.5 ms as the mid point of the RC pulse (and subtracted on input added on output as described by ken) means that you can use a value of +-64 to represent the servo position (or whatever). The nice thing about this sort of range is that you can perform a fair bit of manipulation of values etc. using only 8 bit arithmetic it is easy to put together functions/macros to limit things to this range, create deadbands etc. I've used this system to create simple mixers, and various other systems that require RC inputs to be combined with real world measurements before being used to control an RC servo. just a thought Andy {Original Message removed}