SERVOPOS and variable for the pin

[jl-bot]

@ technical

Hi,

Picaxe can drive many servos. It is excellent. (e.g. the kit "caterpillar" with 18X1 and 8 servos !)

The command SERVO accept a variable which specifies the i/o pin
but not the command SERVOPOS, only a constant.

In the program, with 8 servos it is necessary to create 8 different gosub with SERVOPOS 0, ... SERVOPOS 1,.....
SERVOPOS 2,..... SERVOPOS 3,.... etc SERVOPOS 7,....

with SERVO one gosub is sufficient SERVO x,..... (x =0 to 7 ) syntax OK

In the manual:
" The ‘servo’ command initialises the pin for servo operation and starts the timer.
Once a pin has been initialised, it is recommended to use the ‘servopos’
command to adjust position. This prevents resetting of the timer, which could
cause ‘jitter’ "
(Yes I note this behaviour with my robot )

SERVOPOS is important for good program.

In the future update, can you modify SERVOPOS for it accept also a variable for the pin, if it is possible.


Thanks

(sorry for my english language)

 

[Technical]

This is due to the firmware style and can't be changed, but on later chips like the X2 parts you can already use variables for the pin with servopos.

 

[westaust55]

If you have 8 separate GOSUB calls for SERVOPOS you may be able to restructure with the ON...GOSUB command

As incomplete code for the concept:

SYMBOL ServoPin = b5
SYMBOL Position  = b6

Main:
; here determine with servo pin number to call in the range 0 to 7 for the 8 possibilities
; and define the new servo position - here put in variable b6

ON ServoPin GOSUB Servo0, Servo1, Servo2, Servo3, Servo4, Servo5, Servo6, Servo7

; do other "stuff"
	GOTO Main

Servo0:
	Servopos 0, b6
	RETURN
Servo1:
	Servopos 1, b6
	RETURN
Servo2:
	Servopos 2, b6
	RETURN
Servo3:
	Servopos 3, b6
	RETURN
Servo4:
	Servopos 4, b6
	RETURN
Servo5:
	Servopos 5, b6
	RETURN
Servo6:
	Servopos 6, b6
	RETURN
Servo7:
	Servopos 7, b6
	RETURN

Still needs 8 subroutines but only one program call based upon a ServoPin number

 

[inglewoodpete]

A variation on a theme. The following subroutine code is taken directly from the servo driver of a robotic "person".

Note the subtle difference from WA55's version.

WA55: On <servo> GoSub <label> 'Execution returns to the following statement
IWP: On <servo> GoTo <label> 'Whole block of code is treated as a single subroutine.

Symbol	ServoOffset	= b2	'>w1	servo routines
Symbol	NewPos		= b4	'>w2	servo routines
'
' *** SetServo - Set New Servo Position ********
'
'	Entry:	ServoOffset (0-4 for up to 5 Servos), NewPos (required new position)
'		Note: All servo pins of PICAXE must have previously been initialised
'		Also that the order does not necessarily match to logical pin numbers
'	Exit:	All registers preserved
'
SetServo:On ServoOffset Goto SrvRArm, SrvLArm, SrvNeck, SrvWaist, SrvEyes
	Return			'Any other values
SrvLArm:	ServoPos LArm, NewPos
	Return
SrvRArm:	ServoPos RArm, NewPos
	Return
SrvNeck:	ServoPos Neck, NewPos
	Return
SrvWaist:	ServoPos Waist, NewPos
	Return
SrvEyes:	ServoPos Eyes, NewPos
	Return

 

[jl-bot]

Thanks for the two solutions with olds picaxe

I have tested with 28X2 (simulate) :
"SERVOPOS variable, position " is OK

but:
"SERVOPOS variable, OFF" -----> error syntax
"SERVOPOS B.3, OFF " -----> error syntax
"SERVOPOS 3, OFF " -----> error syntax
and also with other pins B.

with 18M2:

"SERVOPOS variable, position" is OK

"SERVOPOS variable, OFF " --------> error syntax
"SERVOPOS B.3, OFF " is OK and also with other pin B.
"SERVOPOS 3, OFF" is OK and also with other pin B.