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4. BASIC Stamp II Software

(In this section, we go over the major features of the program. For more details, view the entire program (3k bs2). Note that the pin numbers used in the program correspond to the schematic diagram in section 3, above.)

The BASIC Stamp makes serial I/O very straightforward with its serout instruction. A typical use of the instruction is:


  serout MC_SOUT, 32, [$80, 0, LFWD, SPEED]    'Left motor forward at SPEED

The first value, MC_SOUT, specifies the serial output pin to use, which is P10 in our example. The second argument, 32, specifies the settings for the serial output; we use 32 because it specifies the baud rate to be 19,200, which is the maximum rate at which the motor controller can receive. The four values in square brackets are the values sent out over the serial line.

The first two values sent to the motor controller are always hex 80 (128 in decimal) and 0, which let the motor controller know that it is being issued a command. The third value specifies the motor number and direction. To help prevent mistakes with this third parameter, we defined constants for forward and backward for our two motors at the beginning of our program:

  LFWD        con    0     
  LBAK        con    1        
  RFWD        con    2    
  RBAK        con    3

(Of course, which constant gets assigned which number depends on how your robot is wired up and what you call forward and reverse or left and right.) The final parameter in the 4-byte sequence is the speed at which the motor should run, where 0 stops the motor and 127 (7F hex) is full speed.

Note: At the beginning of the program, it is important to reset the motor controller. Make sure the serial line is high before you reset the motor controller:

  high     MC_SOUT        'serial line idle state
  low    MC_RESET    'reset motor controller
  high    MC_RESET

The main loop of the program is rather simple since the robot does not do much. For simplicity, we use the pause instruction to determine the time that the robot backs up or turns, but the BASIC Stamp could potentially be doing something more useful during that time.

loop:    'Go forward till bump something
    serout MC_SOUT, 32, [$80, 0, LFWD, SPEED]    'Left and right motors forward at SPEED
    serout MC_SOUT, 32, [$80, 0, RFWD, SPEED]    '32 indicates 8 bits, no parity, non-inverted, 
                                ' buad rate 19200
    if (RBUMP = 0) then rbumped            'If bumped, turn backward in appropo direction
    if (LBUMP = 0) then lbumped
    goto    loop    

rbumped: 'Turn backward right, then spin left in place for a random time
    serout MC_SOUT, 32, [$80, 0, LBAK, SPEED]        'Turn backward for 1 sec
    serout MC_SOUT, 32, [$80, 0, RBAK, SLOWSPEED]
    pause 1000

    serout MC_SOUT, 32, [$80, 0, LBAK, SPEED]    'Spin in place for random time, TURNTIME
    serout MC_SOUT, 32, [$80, 0, RFWD, SPEED]
    random TURNTIME
    pause (TURNTIME*5) + 250            'pause between 0.25 and 1.5 seconds

    goto loop

lbumped: 'Turn backward left, then spin right in place for a random time
    serout MC_SOUT, 32, [$80, 0, LBAK, SLOWSPEED]    
    serout MC_SOUT, 32, [$80, 0, RBAK, SPEED]
    pause 1000

    serout MC_SOUT, 32, [$80, 0, LFWD, SPEED]
    serout MC_SOUT, 32, [$80, 0, RBAK, SPEED]
    random TURNTIME
    pause (TURNTIME*5) + 250

    goto loop

For more details, view the entire program (3k bs2). Note that the pin numbers used in the program correspond to the schematic diagram above.