Servo - April 2013

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Figure 4

code isn’t that complex. This is not to say that it is easy to write! You will spend a great deal of time tweaking and tuning your timing, and choosing your state steps before your behaviors work properly.

The FSM is a basic cornerstone of embedded programming, so if you are inclined to get a job in automation or embedded engineering, put some time in on these concepts — you’ll need them!

Back to the Hardware

While working with my Roomba, I got tired of my taped-on dead weights falling off and my Roomba stopping every time it changed directions. So, I

Listing 3: DoEscape behavior.

break;

void DoEscape(void)
// Define a bumper response escape behavior
{
  static uint32_t ticker = 0;
  static uint8_t state = 0;
  static uint8_t dir = 0;

if ((mBumpers == 0) && (state ==0))
// Don't do anything if nothing to do
{
  return;
}
if (priority <= escape)
{
  priority = escape;
  switch(state)
  {
 case 0: // record bumper, backup
 dir = mBumpers;
 ticker = millis() + 1000;  // 1 second
 GoBackward();
 GoSong();
 state = 1;
 Serial.print("Bumper dir: ");
 Serial.println(dir,HEX);
 break;

case 2: // choose turn
 // direction
  if (dir == RIGHT)
  {
 Serial.println("spin left");
 SpinLeft();
  }
  else if (dir == LEFT)
  {
 Serial.println("spin right");
 SpinRight();
  }
  else
  {
 Serial.println("ahead");
 SpinRight();
  }
 ticker = millis() + 1000;
 state = 3;
  break;

case 1: // wait for backup
 // done
  if (ticker < millis())
  {
 state = 2;
 Serial.println("Do turn");
  }
case 3: // wait for turn done
  if (ticker < millis())
  {
 state = 0;
 dir = 0;
 priority = idle;
 Serial.println("All done");
  }
  break;