More Servo Woes

[chrisshortys]

Hi guys, I am currently building a projct which uses the analoge input from a 3 axis accelerometer and turns this into a proportional servo output.

I have now managed to get y chip to read ADC input from one input and to put out a servo ouput using a FOR loop.

Now the problem I am having is the FOR loop doesnt seem to be interuptable. So the servo will only respond to a new input once it has reached its current destination. I want to find a way to have the servo change direction before it reaches its end destination.

The second issue i have is the programe seems to freeze at times. The LCD does not update and the programe does not recognise any change in input for a while before suddenly snapping back into life.

Attached below is my code

'***********************************************************************
'*college project to control 2 servo motors from a 3 axis accelerometer*
'***********************************************************************
'*****27/02/09***********************************************************
' V 0.2
' For loop responding to input of ADC
' active ADC inputs displayed on line 2 of lcd
' servo position shown on line 1 of LCD
'***********************************************************************
'** Shows the Connections on the ports of the PIC **********************
'***********************************************************************
'
'A0 = X-AXIS 
'A1 = Y-AXIS
'A2 = Z-AXIS
'A3 = 
'A4 = 
'A5 = 
'
'BO = LCD INTERFACE
'B1 = LCD INTERFACE
'B2 = LCD INTERFACE
'B3 = LCD INTERFACE
'B4 = LCD INTERFACE
'B5 = LCD INTERFACE
'B6 = LCD INTERFACE
'B7 = LCD INTERFACE
'
'C0 = SERVO 1
'C1 = SERVO 2
'C2 = 
'C3 = 
'C4 = 
'C5 =
'C6 =
'C7 =


'***********************************************************************
'****************** DEFINE ADCIN PARAMETERS*****************************
'***********************************************************************

DEFINE ADC_BITS		8		'SETS NUMBER OF BITS IN RESULTS
DEFINE ADC_CLOCK	3		'SET CLOCK SOURCE
DEFINE ADC_SAMPLUS	50		'SET SAMPLING TIME IN US

DEFINE LCD_DREG PORTB 			'Define PIC port used for LCD Data lines
DEFINE LCD_DBIT 4 			'Define first pin of portb connected to LCD DB4
DEFINE LCD_RSREG PORTB 			'Define PIC port used for RS line of LCD
DEFINE LCD_RSBIT 3 			'Define Portb pin used for RS connection
DEFINE LCD_EREG PORTB 			'Define PIC prot used for E line of LCD
DEFINE LCD_EBIT 0 			'Define PortB pin used for E connection
DEFINE LCD_BITS 4 			'Define the 4 bit communication mode to LCD
DEFINE LCD_LINES 2 			'Define using a 2 line LCD
DEFINE LCD_COMMANDUS 2000 		'Define delay between sending LCD commands
DEFINE LCD_DATAUS 50 			'Define delay time between data sent.



SERVOY 		VAR	PORTC.0
SERVOX 		VAR	PORTC.1

YAXIS		VAR	WORD
XAXIS		VAR	WORD
ZAXIS		VAR	WORD

XPRESET		VAR	WORD
YPRESET 	VAR	WORD
ZPRESET		VAR	WORD

B0 		VAR 	WORD
B1 		VAR 	WORD
B2		VAR 	WORD
B3 		VAR 	WORD


TRISA = %00000011			'SETS INPUTS/OUTPUTS FOR BANK A
TRISB = %00000000			'SETS INPUTS/OUTPUTS FOR BANK B
TRISC = %00000000			'SETS INPUTS/OUTPUTS FOR BANK C

ADCON1 = %00000110			'SETS THE ANALOGUE/DIGITAL INPUTS TO BANK A

PORTA = %00000000			'SETS THE INITIAL VALUE OF BANK A
PORTB = %00000000			'SETS THE INITIAL VALUE OF BANK B
PORTC = %00000000			'SETS THE INITIAL VALUE OF BANK C


'**************************************************************************
'				CENTER THE SERVO
'				****************
' Pause for one second to allow initalisations
' Clear the LCD display
' Center Servo 1 and then servo 2
'
'**************************************************************************

PAUSE 1000
LCDOUT "STARTING"
pause 1000
LCDOUT $FE, 1

CENTER:					'NEW SUBROUTINE FOR SETTING THE SERVO
	FOR B0 = 1 TO 100		'MOVES THE SERVO FROM ITS 0 TO ITS 100 MARK
	PULSOUT SERVOY, 150		'
	PAUSE 20			'
	NEXT	

	FOR B1 = 1 TO 100		'Pans the servo from 0 to a halfway point of 100
	PULSOUT SERVOX, 150		'
	PAUSE 20			'
	NEXT

			


'**************************************************************************
'				setup ADC
'				*********
' reads the ADC ports and sets the initial values for calculations
'**************************************************************************
STARTUP:				

ADCIN 0, B2				' reads in the ADC on PORT A.0 and sends it to memory location B2
ADCIN 1, B3				' reads in the ADC on PORT A.1 and sends it to memory location B3


gosub servomove

'**************************************************************************
'				Servo calculations
'				******************
' 
'
'**************************************************************************

MAIN:

ADCIN 0, B2				' Reads in the PORT A.0 ADC AND STORES THE VALUE IN B2
ADCIN 1, B3				' READS IN THE PORT a.1 ADC AND STORES THE VALUE IN B3

XPRESET	=	B2 + 50

If Xpreset > 92 then
goto positive
endif

if xpreset < 92 then
goto negative
endif


positive:
	FOR B0 = B0 TO XPRESET
	PULSOUT SERVOY, B0
	PAUSE 20
	gosub servomove
	NEXT

goto main



negative:
	FOR B0 = B0 TO xpreset STEP -1
	PULSOUT SERVOY, B0
	PAUSE 20
	gosub servomove
	NEXT

goto main


'
'
''*******************************************************************************************************************
'			SERVOMOVEMENT CONTROL
'			*********************
' MOVES BOTH SERVOS FOR BOTH X AND Y MOVEMENT
' CREATES THE NEW X AND Y PRESETS FOR THE CALCULATIONS
' UPDATES THE LCD DISPLAY
'*******************************************************************************************************************
SERVOMOVE:
'
'	PULSOUT SERVOY, B1		' SENDS THE NEW VALUE FOR SERVO Y 
'
'
'	PULSOUT SERVOX, B0		' SENDS THE NEW VALUE FOR SERVO X
'			
'

ADCIN 0, B2				' Reads in the PORT A.0 ADC AND STORES THE VALUE IN B2
ADCIN 1, B3				' READS IN THE PORT a.1 ADC AND STORES THE VALUE IN B3



LCDOUT $FE, 2				' SENDS THE COMMAND TO THE LCD TO MOVE TO THE START OF THE FIRST LINE

LCDOUT "Servo Pos= ",DEC3 B0		' SENDS THE DATA FOR THE X AXIS TO THE LCD ON THE FIRST LINE

LCDOUT $FE, $C0				' MOVES THE CURSUR OF THE LCD TO THE START OF THE SECOND LINE

LCDOUT "Y = ",DEC3 B2, " X = ",DEC3 B3		' SENDS THE DATA FOR THE Y AXIS TO THE LCD ON THE SECOND LINE

RETURN					' RETURNS TO THE PREVIOUS BLAAAAAAAAAAAAAAAAAAAAAAH


GOTO MAIN



END

[aratti]

Tray this it should help.

positive:
	While B0 <> XPRESET
	B0=B0+1
        PULSOUT SERVOY, B0
	PAUSE 20
	gosub servomove
	wend

goto main



negative:
	While B0<>xpreset
	B0=B0-1
        PULSOUT SERVOY, B0
	PAUSE 20
	gosub servomove
	wend

goto main

Al.

[chrisshortys]

Nope this results in the servo panning uncontrolled trying to pass its limits. I havnt ever used a while loop before but assumed the piece of code you gave me should of fitted in where my current for loops where.

If so i shall have a play tommorow and see what i can come up with

[Archangel]

Hi Chris,
I have only a little experience with servos, and do not have my computer at hand, but the best I remember, if I sent a number to my servo it executed fully before accepting a new value, so I am thinking if you send a count to the servo something like 1500, 1510, 1520 . . . to cause movement you can snuggle an interrupt between the numbers.
EDIT: after reading your code, looks like pretty much what you are doing. I'm empty.

Now the problem I am having is the FOR loop doesnt seem to be interuptable. So the servo will only respond to a new input once it has reached its current destination. I want to find a way to have the servo change direction before it reaches its end destination.

I see no interrupt in your code, Why would you be able to stop it? I never have been able to hijack the count variable in a for next loop, you might try using an interrupt routine and clearing the variable in there, I do not know if it will work though.

The second issue i have is the programe seems to freeze at times. The LCD does not update and the programe does not recognise any change in input for a while before suddenly snapping back into life.

Could be latency, could be Breadboard issues where stray capacitance stops the oscillator, could be power supply causing PIC brownout reset, I see no config statement so I assume you are using default config, . . . could be GOTO MAIN at the end of servomove when you used gosub to get there, causing a stack overflow, and eventual reset. . . . On closer inspection looks like you have a return and goto main in there . . . I don't know how that would affect operation if at all since theoretically the code should never go past the return, but who knows? Computers (and PICs) are stupid, but not sloppy, they only do what you tell them to do, whether intentionally or not.
Keep us posted, I would like to see your Final Cut, looks like it would make a cool VR control for a camera in an RC heli.

[Acetronics2]

Hi, Chris

A servomotor has it's own signal limitations ...

from 800 to 2200 µs pulse ( STD ) ... so unpredictable behaviour can occur outside those limits ...

ADCIN 0, B2				' Reads in the PORT A.0 ADC AND STORES THE VALUE IN B2
ADCIN 1, B3				' READS IN THE PORT a.1 ADC AND STORES THE VALUE IN B3

XPRESET	=	B2 + 50

your accelerometer is an analog one, Ok ... but ADCIN can give a result between 0 and 256 ...

so, the servo signal range is not guaranteed to be in the " valid" range.

Now , you read Twice the accelerometer in one cycle ... not really a problem, but it's not compulsory here.

BTW ... Which Pic and Accelerometer do you use ???

Alain

[chrisshortys]

Thanks for all the replies i shall try and go through them now

your accelerometer is an analog one, Ok ... but ADCIN can give a result between 0 and 256 ...

so, the servo signal range is not guaranteed to be in the " valid" range.

BTW ... Which Pic and Accelerometer do you use ???

Alain

Firstly i understand that the ACDIN can give the range from 0-256 how ever the accelerometer is not capable of giving a value of 0-5v, I can't remember the exact voltages as theyre at work but the values i receive on the ACDIN when moving from one limit to the other are 45-128. This is the reason i add a value to the number to try and keep the server centeral(yes i know its not the correct value yet :P ).

The Pic I am using is a 16f876A
and the accelerometer is a prototyping board which i brought from sure electronics http://cgi.ebay.co.uk/3-Axis-low-g-A...1%7C240%3A1318

Hi Chris,
I have only a little experience with servos, and do not have my computer at hand, but the best I remember, if I sent a number to my servo it executed fully before accepting a new value, so I am thinking if you send a count to the servo something like 1500, 1510, 1520 . . . to cause movement you can snuggle an interrupt between the numbers.
EDIT: after reading your code, looks like pretty much what you are doing. I'm empty.

I see no interrupt in your code, Why would you be able to stop it? I never have been able to hijack the count variable in a for next loop, you might try using an interrupt routine and clearing the variable in there, I do not know if it will work though.


Could be latency, could be Breadboard issues where stray capacitance stops the oscillator, could be power supply causing PIC brownout reset, I see no config statement so I assume you are using default config, . . . could be GOTO MAIN at the end of servomove when you used gosub to get there, causing a stack overflow, and eventual reset. . . . On closer inspection looks like you have a return and goto main in there . . . I don't know how that would affect operation if at all since theoretically the code should never go past the return, but who knows? Computers (and PICs) are stupid, but not sloppy, they only do what you tell them to do, whether intentionally or not.
Keep us posted, I would like to see your Final Cut, looks like it would make a cool VR control for a camera in an RC heli.

Yer i think that is the problem the FOR loop is not very interuptable. Thats somthing im going to change once i get time to play with it again.
Shouldnt be a problem with latency as i only ever use veroboard though i havnt placed any capacitors across the crystal so i shall do that asap to see if that helps.
Power supply wise i have tried the circuit on several different powersupplies both at work and at home, the only issue i had there was i had the current limiter at around 100 mA and the servo seems to draw a considerable amount to trip that on its first start up! But hat has now been rectified with a 470 uF across the power rails next to the servo and upping the current limiter.

I shall lso try removing the goto main which was left in from a older attempt but i cant see that command even being looked at but its worth a try!

Orriginally i had planned to make a Pan-Tilt head for a camera but im now looking at making this into a robotic arm kind of setup with possibly strain gauges to detect a hand closing..... i dont know that somthing for later