Файл: Advanced Robotics with the Toddler (Paralax, student guide, v1.3, 2004).pdf

Chapter #5: Following Light · Page 103

These routines use the movement routines initially presented in the prior chapter. The Toddler can make smaller turns.

Your Turn

√Enter and run Program Listing 5.2.

√Shine a bright flashlight in front of the Toddler. When you move the flashlight, the Toddler should rotate so that it’s pointing at the flashlight beam.

√Instead of using a flashlight, use your hand to cast a shadow over one of the photoresistors. The Toddler should rotate away from the shadow.

√In a darker area, not only will the photoresistor values be larger, so will the difference between them. You may have to increase the deadband in low ambient light to detune the Toddler to small and changing variations in light. The lower the light levels, the less you need the PAUSE statements. If the Toddler’s performance starts to decrease, it’s probably because the time between pulses has exceeded 40 ms. The first line of defense for this problem is to reduce the PAUSE period in each subroutine to zero. The second line of defense is to check photoresistors during alternate pulses. That way, after the first pulse, the right photoresistor could be checked. Then, after the second pulse, the left photoresistor could be checked. You can try your hand at developing code that does this in the Challenges section.

√Experiment with different ambient light levels and their effect on deadband by trying this experiment in lighter and darker areas. In lighter areas, the deadband value can be made smaller, even zero. In darker areas, the deadband value should be increased.

Swap the conditions in the second and third IF...THEN statement in Program 5.2. Then re-run the program. Now your Toddler points away from the light.

Page 104 · Advanced Robotics with the Toddler

ACTIVITY #3: FOLLOWING THE LIGHT

Programming the Toddler to follow light requires that only a few modifications to Program Listing 5.2 be made. The main change is that measurements within the deadband resulted in no motion in Program Listing 5.2. In Program Listing 5.3, when the difference between RC times falls within the deadband, it results in forward motion. Let’s see how it works.

'-----[ Title ]-----------------------------------------------------------

'Toddler Program 5.3: Follow the Light

'Marching toward the light

'{$STAMP BS2}

'{$PBASIC 2.5}

'-----[ I/O Definitions ]-------------------------------------------------

'A xx indicates the end of a list.

'These are used with the Movement routine.

'------ Movement Value Tables ------

'These can be used with the Movement routine.

'The tables can contain Basic Movement Codes.

'Note: ALL movement tables must be in this section

'------ Basic Movement Codes ------

'Used in Movement tables.

'Referenced below using LOOKUP statement.

'Measure difference between RPhotoVal and LPhotoVal, decide what to do

IF ABS(LPhotoVal-RPhotoVal) > DeadBand THEN check_dir

'Check if difference between RC times is within the deadband

'If yes, then forward. If no then skip to check_dir subroutine.

walk_forward: Mx = Forward

GOSUB Movement goto main

' Select right_turn or left_turn depending on which RC time is larger

'-----[ Subroutines ]-----------------------------------------------------

'----- Movement: Move feet using DATA table referenced by Mx -----

'

'Input: Mx = movement table index, table ends in xx

'or

'Mx = submovement table index, table ends in xx

'Note: All submovment tables come after the movment tables in this file.

Movement:

IF Mx < BasicMovements THEN SetupMovement

'debug hex Mx, " Movement ", dec MoveLoop, " of ", dec MoveLoopLimit,cr IF Mx < BasicMovements THEN MovementLoop

SubMovementDone:

NEXT

IF Mx < BasicMovements THEN MovementLoop

MovementDone:

NEXT

RETURN

DoMovement:

'debug " ", dec Dx, " action",cr

BRANCH Dx,[TiltLeft,TiltCenter,TiltRight,StrideLeft,

StrideCenter,StrideRight]

' will fall through if invalid index

RETURN

' ---- Movement routines can be called directly ----

TiltLeft:

NewValue = LeftTilt

GOTO MovementTilt

TiltCenter:

NewValue = CenterTilt

GOTO MovementTilt

TiltRight:

NewValue = RightTilt

MovementTilt: