QTI line follower appkit documentation v2.0

' {$STAMP BS2}

' {$PBASIC 2.5}

' CheckQtiSubroutine.bs2

' Displays QTI sensor states. 0 means white surface, 1 means

' black.

qtis VAR Nib ' qti black/white states

OUTB = %1111 ' Set OUTB bits to 1

DEBUG CRSRX, 8, "FMMF", CR, ' Display bit positions

CRSRX, 8, "LLRR", CR

DO ' Main DO...LOOP

GOSUB Check_Qtis ' Get QTI states

DEBUG BIN4 ? qtis, CRSRUP ' Display QTI states

PAUSE 100 ' 1/10 s delay

LOOP

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 ' Store QTI outputs in INB

RETURN

The BASIC Stamp has a variety of parallel I/O control features that make it possible to perform

operations on groups of I/O pins. CheckQtiSubroutine.bs2 uses the BASIC Stamp's

DIRB and OUTB

variables to control the directions and output states of the I/O pins P7, P6, P5, and P4. When these I/O

pins are set to input with

DIRB = %0000, the program also takes a snapshot of the binary states these

I/O pins sense as a result of the four QTIs' R pin voltages with the command

qtis = INB.

Simple Line-Following

LineFollowWithCheckQtis.bs2 is designed to start following a line as soon as you place a QTI over the

electrical tape. It will stop line following as soon as it runs out of electrical tape. Start with an easy

course, like a large S shape as shown below. If the QTIs passed the "Testing for Line Detection" tests, it

should 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 QTIs

over the electrical tape.

If your QTIs’ cables are reversed, the Boe-Bot will appear to try to jump off the line at the first

opportunity. Otherwise, it should faithfully follow the line until it reaches the end of the tape.