QTI Line Follower AppKit for the Boe-Bot (#28108) - Parallax Inc

' {$STAMP BS2}' {$PBASIC 2.5}' CheckQtiSubroutine.bs2' Displays QTI sensor states. 0 means white surface, 1 means' black.qtis VAR Nib' qti black/white statesOUTB = %1111 ' Set OUTB bits to 1DEBUG CRSRX, 8, "FMMF", CR,CRSRX, 8, "LLRR", CRDOGOSUB Check_QtisDEBUG BIN4 ? qtis, CRSRUPPAUSE 100LOOP' Display bit positions' Main DO...LOOP' Get QTI states' Display QTI states' 1/10 s delayCheck_Qtis:' Result -> qtis variable. 0 means white surface, 1 means' black surface.DIRB = %1111' P7..P4 -> outputPAUSE 0' Delay = 230 usDIRB = %0000' P7..P4 -> inputPAUSE 0' Delay = 230 usqtis = INB ' Store QTI outputs in INBRETURNThe BASIC Stamp has a variety of parallel I/O control features that make it possible to performoperations on groups of I/O pins. CheckQtiSubroutine.bs2 uses the BASIC Stamp's DIRB and OUTBvariables to control the directions and output states of the I/O pins P7, P6, P5, and P4. When these I/Opins are set to input with DIRB = %0000, the program also takes a snapshot of the binary states theseI/O pins sense as a result of the four QTIs' R pin voltages with the command qtis = INB.Simple Line-FollowingLineFollowWithCheckQtis.bs2 is designed to start following a line as soon as you place a QTI over theelectrical tape. It will stop line following as soon as it runs out of electrical tape. Start with an easycourse, like a large S shape as shown below. If the QTIs passed the "Testing for Line Detection" tests, itshould navigate the course with ease.√√Enter and run LineFollowWithCheckQtis.bs2.Place the Boe-Bot on the course so that in straddles the line with the mid left and mid right QTIsover the electrical tape.If your QTIs’ cables are reversed, the Boe-Bot will appear to try to jump off the line at the firstopportunity. Otherwise, it should faithfully follow the line until it reaches the end of the tape.Copyright © Parallax Inc. QTI LIne Follower AppKit (#28108) v2.0 3/23/2009 Page 5 of 6

' {$STAMP BS2}' {$PBASIC 2.5}' LineFollowWithCheckQtis.bs2' Navigates based on values acquired with the' Check_Qtis subroutine.qtis VAR Nib' black/white statesOUTB = %1111 ' Set OUTB bits to 1DO' Main DO...LOOPGOSUB Check_Qtis' Get QTI statesSELECT qtisCASE %1000PULSOUT 13, 650PULSOUT 12, 650CASE %1100PULSOUT 13, 750PULSOUT 12, 650CASE %0100PULSOUT 13, 800PULSOUT 12, 650CASE %0110PULSOUT 13, 850PULSOUT 12, 650CASE %0010PULSOUT 13, 850PULSOUT 12, 700CASE %0011PULSOUT 13, 850PULSOUT 12, 750CASE %0001PULSOUT 13, 850PULSOUT 12, 850CASE ELSEPAUSE 3ENDSELECTLOOPCheck_Qtis:' Result -> qtis variable.' 0 means white surface' 1 means black surface.DIRB = %1111PAUSE 0DIRB = %0000PAUSE 0qtis = INBRETURN' Control servo' speeds/directions' Rotate right' Pivot right' Curve right' Straight ahead' Curve left' Pivot left' Rotate left' Do nothing' P7..P4 -> output' Delay = 230 us' P7..P4 -> input' Delay = 230 us' Store QTI outputs' in INBKeep in mind that this is a bare-bones linefollowing example. Making it robust andversatile is up to you. The Boe-Bot startsmaneuvers when it sees one of the caseslisted in the SELECT...CASE statement.This is convenient for a simpledemonstration program because the Boe-Bot doesn't go anywhere when it is on anall white or all black surface. It only startsnavigation when it detects a line. You canadd extra code, especially in the form ofCASE statements to deal with specialsituations and more complex courses.√√√√√Try other courses to test the limitsof the program.Try modifying the program tosolve courses that the unmodifiedprogram could not solve.Modify the program so that itsmoothes out the Boe-Bot'sresponses to changes in the line'sdirection. Your code should takesteps toward a maximum speedeach time it detects that a givenpattern is detected.Detect intersections and makerandom turns.Challenge a friend, or set up aBoe-Bot line followingcompetition.Copyright © Parallax Inc. QTI LIne Follower AppKit (#28108) v2.0 3/23/2009 Page 6 of 6