Servo - December 2014

Listing 3: PropBot_Navigate.

int main() { // main function
  int turret = 14; // Standard servo connected to P14
  int dlay = 2000; // Wait delay: 2 seconds
  while(1) {
 servo_angle(turret, 900); // Servo to center
 pause(dlay); // Wait for delay period
 servo_angle(turret, 0); // Servo turn clockwise
 pause(dlay); // Wait
 servo_angle(turret, 1800); // Turn counter-clockwise
 pause(dlay); // Wait
  }
}
 #include "simpletools.h"
 #include "ping.h"
 #include "servo.h"

Figure 6. Connection of the turret sensor into the P14 header along the top of the Propeller Activity board.

int main() {
  int turretPin = 14;
  int pingPin = 15;
  int dlay = 2000;
  while(1) {
 servo_angle(turretPin, 900);
 doPing(pingPin,dlay);
 servo_angle(turretPin, 0);
 doPing(pingPin, dlay);
 servo_angle(turretPin, 1800);
 doPing(pingPin, dlay);
  }
}
 
int doPing(int pinNum, int waitDelay) {
  pause(750);
  int Dist = ping_inches(pinNum);
  print("Dist = %d\n", Dist);
  pause(waitDelay);
  return Dist;

“settling” time to allow the servo to cease any jittery movement once stopped. Note that I’ve used user-defined variables to set both the I/O pin connecting to the servo and the delay period. This is good practice when your programs refer to the same data multiple times. If a change needs to be made, you only have to update the variable definition rather than every separate instance of the data throughout the program. That is, instead of: any additional extensions or wiring. Note the configuration of the jumper next to the P14/P15 connectors. To operate the turret servo at the full 6V of the PropBot’s battery pack, be sure to move the jumper from Vin to 5V.

Listing 2: PropBot_Test TurretServo shows a demo program for rotating the turret forward, fully right, and fully left. Some wait delays are included to allow time for the servo to transition to its new position. At 6V, these standard servos move 60 degrees in about 250 milliseconds. The two second delay in the test program is for demonstration purposes only; in actual practice, you want to limit the delay to only what’s needed to transit the servo to its new position, along with a slight amount of

servo_angle(14, 900);

to rotate the turret on P14 to the center, you can use:

int turret = 14;

so whenever you want to change the position of the turret, use the variable name instead, as in:

servo_angle(turret, 900);

Listing 2: PropBot_TestTurretServo.

#include "simpletools.h" // Include simpletools library
#include "servo.h" // Include servo library

This moves the servo connected to pin P14 to position 900 (which means centered). As noted elsewhere in the PropBot_Test TurretServo program, the values 0 and 1800 move the servo fully clockwise and counter-clockwise, respectively. Listing 3: PropBot_TurretTurnAndPing demonstrates combining both the Ping and the turret servo functions, rotating the servo center, right, and left, and