Conditional statements and QTI's

gbd28 · 2009-12-11 23:19

I'm working with the line follow code that is supplied with the QTI sensor kit. It works great but I have two situations where the sensors read

CASE %1110

and I need to distinguish between them so that I can run different subroutines at different times. I have tried using "IF THEN" statements but I am not
getting the desired results. Is there some way to make the "case" both a condition and a variable? I am new to pbasic and would appreciate any help that is offered.

Jessica Uelmen · 2009-12-12 00:55

Hi gbd28,

What are the two conditions that causes the sensors to read %1110, and what makes them different? If you attach the code that you have, it can help us get a better understanding of what you want to do.

One solution would be to have the CASE %1110 go to a subroutine with IF...THEN statements to make another decision based on other parameters. But also keep in mind that you can only nest 4 subroutines before the program will get lost.

Hope this helps.

-- Jessica

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Jessica Uelmen
Education Department
Parallax Inc.

gbd28 · 2009-12-13 00:34

Thanks for your reply. The two conditions are both both 90 degree left turns. But I need the boebot to pause and activate a servo the first time it encounters the case %1110 before returning to the line follow routine. The second time it detects case %1110 I need the boebot to pause and turn 45 degrees to the right, activate the servo, then return to the original line by turning approximately 135 degrees then returning to the line follow routine.

I have been successful at programing both of these individual series of operations with sub routines but have not found a way to have both perform.

The code is

' {$STAMP BS2}
' {$PBASIC 2.5}

qtis VAR Nib             'qti black/white states

OUTB = %1111

DO
  GOSUB Check_Qtis

  SELECT qtis

CASE %1000
PULSOUT 13, 650                      '13 left
PULSOUT 12, 650                      '12 right
CASE %1100
PULSOUT 13, 750
PULSOUT 12, 650
CASE %0100
PULSOUT 13, 800
PULSOUT 12, 650
CASE %0110
PULSOUT 13, 840
PULSOUT 12, 650
CASE %0010
PULSOUT 13, 850
PULSOUT 12, 700
CASE %0011
PULSOUT 13, 850
PULSOUT 12, 750
CASE %0001
PULSOUT 13, 850
PULSOUT 12, 850
CASE %1110
PAUSE 500                   ' Stop for 1/2 second
GOSUB second_base     ' Turn approximately 45deg clockwise, resulting in right turn
GOSUB servo14            ' Activate continuous servo for firing mechanism
GOSUB line_return1      ' Turn approximately 135deg counter-clockwise, resulting in left turn and returning to line follow
counter VAR Word
FOR counter = 1 TO 25  ' Servos rotate simultaniously in opposite direction
PULSOUT 12, 650          ' causing unidirectional motion
PULSOUT 13, 750
PAUSE 20
NEXT
CASE %1111
PAUSE 500                   ' Stop for 1/2 second
GOSUB third_base        ' Turn approximately 90deg clockwise, resulting in right turn
'PAUSE 1000
GOSUB servo14            ' Activate continuous servo for firing mechanism
GOSUB line_return2      ' Turn approximately 135deg counter-clockwise, resulting in left turn and returning to line follow
CASE %0000
PULSOUT 13, 750
PULSOUT 12, 650
CASE ELSE
  PAUSE 3
ENDSELECT

LOOP
'----------TURN TO SHOOT @ 2ND BASE SUBROUTINE---------
second_base:
FOR counter = 1 TO 38 ' Servos rotate simultaniously in opposite direction
PULSOUT 13, 850       ' causing unidirectional motion
PULSOUT 12, 850
PAUSE 0
NEXT
RETURN
'----------TURN TO SHOOT @ 3RD BASE SUBROUTINE---------
third_base:
FOR counter = 1 TO 80 ' Servos rotate simultaniously in opposite direction
PULSOUT 13, 850       ' causing unidirectional motion
PULSOUT 12, 850
PAUSE 0
NEXT
RETURN
'----------SERVO 14 SUBROUTINE-----------------
servo14:
FOR counter = 1 TO 1000
PULSOUT 14, 850
NEXT
PAUSE 500
RETURN
'----------LINE RETURN 1 SUBROUTINE---------
line_return1:
FOR counter = 1 TO 113 ' Servos rotate simultaniously in opposite direction
PULSOUT 13, 650       ' causing unidirectional motion
PULSOUT 12, 650
PAUSE 0
NEXT
RETURN
'----------LINE RETURN 2 SUBROUTINE---------
line_return2:
FOR counter = 1 TO 150 ' Servos rotate simultaniously in opposite direction
PULSOUT 13, 650       ' causing unidirectional motion
PULSOUT 12, 650
PAUSE 0
NEXT
RETURN

Check_Qtis:
  'Result -> qtis variable. 0 means white surface, 1 means
  'black surface

DIRB = %1111              'P7..P4 -> output
PAUSE 0                   'delay = 230 us
DIRB = %0000              'P7..P4 -> input
PAUSE 0                   'Delay = 230 us
qtis = INB

RETURN

I hope this more clearly defines my difficulty. Thanks you again for any and all help

sailman58 · 2009-12-13 13:41

There are probably more elegant methods of doing this, but the obvious one to me would be to set up a counter initialized to zero. Use an if to check the value in your case %1110 statement. The first time through, increment the counter in the sub routine.

I know this is the condensed version, but if you need more detail and nobody else chimes in before I return from my trip today, I can talk more then.

Gotta run,

Ron aka sailman58

Conditional statements and QTI's

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