Electrical machinery = Limit switch , Pbasic = ? HELP

Jeff Boertjes

I am setting up a stepper motor to rotate another component in porportion to a distance variable input, under a range of·distances the stepper rotates forwards, under·another range of distance values it rotates·reverse. my problem is that the additional component which the stepper motor is rotating has a limited range of rotation. I was wondering if anyone could show me how to design into my program a variable to keep track of the position of the motor ( of its 48 steps ) and implement somekind of Pbasic "limit switch", possibly in some kind of For..next type of solution·so that it will only rotate forwards to a certain step and then be unable to rotate further forward despite the distance variable being at a range that would otherwise make the stepper continue to rotate forwards. and vice versa so that once at the minimum it can no longer continue to step in reverse.

' {$STAMP BS2}
' {$PBASIC 2.5}
DIST VAR Byte·················································· ·'variable used to store DIRRS result
T VAR Byte························································ 'variable used for 30ms warm-up/wait time of DIRRS
OUTPUT 0························································· ·'pin 0 connects to pin 2 (Vin: Output pin of Micro-controller.) of DIRRS
INPUT 1···························································· ·'pin 1 connects to pin 4 (Vout: Input pin of micro-controller.) of DIRRS
Phase VAR OUTB··············································· ·· ' phase control outputs variable, nibble size
idx VAR Byte······················································ ·' loop counter
stpIdx VAR Nib··················································· ·' step pointer
Steps DATA %0011, %0110, %1100, %1001············· 'stepping data directive stored in eeprom
Setup:······························································ ·'
DIRB = %1111····················································· ' makes P4..P7 outputs
start:································································· "
HIGH 0······························································ ·'vin high-low transition
PAUSE 3···························································· ·'waiting for high to be recognized
LOW 0······························································ ·'
FOR T= 1 TO 30················································· ·'begin 30ms wait
PAUSE 1·························································· · 'pauses 1 ms
IF IN1=1 THEN·················································· · 'vout is high, dist data available
ENDIF······························································ ·'no endif, DIRRS continuously monitors dist
NEXT······························································· ·'
SHIFTIN 1,0,2, [noparse][[/noparse]dist\8]········································ 'shift 8 bits into dist via pin p1, dist value=0-255
······································································ ·'clocking with p0, msb first
DEBUG "distance= ", DEC4 dist, HOME····················· 'display dist's 4 most significant digits in DEBUG window, not scrolling

main:
IF (dist <=50 ) THEN GOTO start···························· 'If dist is less then or equal to 50 do nothing, continues monitoring dist
IF (dist· <=175 ) THEN· FOR idx = 1 TO 2················· 'if dist is less then or equal to 175 step forward by 1 step
GOSUB Step_Fwd··············································· ·' rotate clockwise 1 step
NEXT······························································· · '
IF (dist >=176 ) THEN FOR idx = 1 TO 2···················· ·'if dist is greater then or equal to 176 step reverse by 1 step
NEXT······························································ ·· '
GOSUB Step_Rev················································ ·' rotate counter clockwise 1 step
GOTO start······················································· ·'loop program
END·································································· 'no end command, program loops indeffinitley
Step_Fwd:
stpIdx = stpIdx + 1 // 4······································· ·' point to next step by step pointer= step pointer + 1 modulus 4
GOTO Do_Step
Step_Rev:
stpIdx = stpIdx + 3 // 4········································ ·' point to previous step by step pointer= step pointer + 3 modulus 4
GOTO Do_Step
Do_Step:
READ (Steps + stpIdx), Phase································· 'output new phase data based on current data directive in use + StpIdx
RETURN······························································ ·'loop to beginning of program

Franklin

The problem with a software limit switch is that you need to know where the component is when you start. That will be your first assignment.

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- Stephen

Jeff Boertjes

that can be assumed to be 0 degrees/steps as the additional component and stepper motor can be physically manipulated before running the program.

Franklin

What I'm saying is the first time you forget to physically manipulate the component.. BLOWIEE!

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- Stephen

Unsoundcode

You could keep track of the motor position in each of the sub routines Step_Fwd and Step_Rev. Assuming the start position was fully reversed and it was assigned a value of step zero

Motor_Position VAR Byte

Step_Fwd:
Motor_Position = Motor_Position +1
IF Motor_Position =49 THEN Motor_Position=48 : RETURN
stpIdx = stpIdx + 1 // 4········································ ' point to next step by step pointer= step pointer + 1 modulus 4
GOTO Do_Step

Step_Rev:
Motor_Position = Motor_Position -1
IF Motor_Position =255 THEN Motor_Position=0 : RETURN
stpIdx = stpIdx + 3 // 4········································· ' point to previous step by step pointer= step pointer + 3 modulus 4
GOTO Do_Step

a homing switch at one of the extremes would be a nice feature

Jeff T.