I used to play with that little Cybot project that came with the Eaglemoss publications "Real Robots" magazine.

Recently I got very board with it, so, being me, I ripped out its microprocessors, leaving only the sensory and motor control components, and introduced the beloved PIC!

I began with a program that would allow the robot to follow a black line on a white surface.

Check HERE and HERE for the schematics.

It's very simple, the pair of IR sensors feed into a comparator, the black line absorbs IR, the white reflects. When the robot is on the edge of the line, the result would be, one IR sensor at logic 1 and the other at logic 0. The comparator outputs logic 1 to the processor when one input is at logic 1 and the other is a logic 0, otherwise it will output logic 0.

I spend some time thinking about this one, and after a lesson on Fuzzy Logic in IT class at school I finally got it!

So here's how:

Code:
'****************************************************************
'*  Name    : LineFollow.BAS                                    *
'*  Author  : CIT Systems (Darren Carter)                       *
'*  Notice  : Copyright (c) 2009 CIT Systems (Darren Carter)    *
'*          : All Rights Reserved                               *
'*  Date    : 2009/02/02                                        *
'*  Version : 1.0                                               *
'*  Notes   : Include in PIC-Bot Processor                      *
'*          :                                                   *
'****************************************************************

'Line Follow loop    
LineFollow:
    Lcdout $FE, $C0, "~~ LiNe FoLlOw ~~"    ' Display current mode on LCD.
    Lcdout $FE, $94, "...Scan Line..."      ' Tell user line is being followed.
    low RHF                                 ' Stop right motor.
    low LHF                                 ' Stop left motor.
    PWM LHF,60,18                           ' Move slightly RIGHT.
    pause 100                               ' Take a break.
    if linecom = 0 then gosub moveleft      ' Check the line, if you no on it, adjust LEFT, otherwise, continue.
    
    low RHF                                 ' Stop right motor.
    low LHF                                 ' Stop left motor.
    PWM RHF,60,18                           ' Move slightly LEFT.
    pause 100                               ' Take a break.
    if linecom = 0 then gosub moveright     ' Check the line, if you no on it, adjust RIGHT, otherwise, continue.
    
    gosub chkctrl                           
    goto linefollow                         ' Repeat the process
    
MoveLeft:
    Lcdout $FE, $94, "Correct Left"         ' Tell user, correcting LEFT.
    repeat                                  
        low RHF                             ' Stop right motor.
        low LHF                             ' Stop left motor.
        PWM RHF,60,20                       
        pause 100                           ' Take a break.
    until linecom = 1                       ' Do this until back on line.
    pause 50                                ' Take a break, and get ready to move ahead by adjusting a little more LEFT.
    low RHF
    low LHF
    PWM RHF,60,18
    return                                  ' Go back to LineFollow loop.
    
MoveRight:
    Lcdout $FE, $94, "Correct Right"        ' Tell user, correcting RIGHT.
    repeat                                  
        low RHF                             ' Stop right motor.
        low LHF                             ' Stop left motor.
        PWM LHF,60,20                       ' Move a little RIGHT.
        pause 100                           ' Take a break.
    until linecom = 1                       ' Do this until back on line.
    pause 50                                ' Take a break, and get ready to move ahead by adjusting a little more LEFT.
    low RHF
    low LHF
    PWM LHF,60,18
    return                                  ' Go back to LineFollow loop.
    
end
As you can see, its quite simple, Fuzzy Logic... If the processor is doing one thing, and an error occurs, fix it by doing the opposite.

I've tested this a couple of time, sometimes the robot does move off course and gets lost, but this just a matter of timing and sensitivity, i.e. the motors move too quickly or move the robot too far for the processor and IR sensor to react to change, and/or reaction from the input from the comparator is happens too quickly, so a kind of "debounce" might be necessary.

It's all a matter of trial and error, lots of time, and PIC flashing until it eventually reaches its 2 000 000 000 threshold, LOL but that's what hobby robotics is all about.