Hello,
I'm using the below code and it works.
the code uses the PING))) sensor to read the distance from an object.
the distance then converted to PWM duty cycles.
then I feed the PWM into an H-bridge chip to drive the motor.
NOTE: if the object moves further away from the car, then the car accelerate and maintain (a minimum distance of 25 cm) with the moving object. {i.e. tailing the object}
THE QUESTION:
HOW CAN I DO THIS USING PI (of the PID library)?
I've looked at the "Arduino Playground - PIDLibrary" and I still don't know how to implement or start programming.
all I know is my set point is the 25 cm obviously.
THE CODE:
/Ping))) Sensor + PWM/
// sensor's output:
const int pingPin = 7;
// PWM output connected to digital pin 9
int pwmPin = 9;
void setup() {
// initialize serial communication:
Serial.begin(9600);
}
void loop()
{
// establish variables for duration of the ping,
// and the distance result in inches and centimeters:
long duration, inches, cm;
int x;
// The PING))) is triggered by a HIGH pulse of 2 or more microseconds.
// Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
pinMode(pingPin, OUTPUT);
digitalWrite(pingPin, LOW);
delayMicroseconds(2);
digitalWrite(pingPin, HIGH);
delayMicroseconds(5);
digitalWrite(pingPin, LOW);
// The same pin is used to read the signal from the PING))): a HIGH
// pulse whose duration is the time (in microseconds) from the sending
// of the ping to the reception of its echo off of an object.
pinMode(pingPin, INPUT);
duration = pulseIn(pingPin, HIGH);
// convert the time into a distance
inches = microsecondsToInches(duration);
cm = microsecondsToCentimeters(duration);
Serial.print(inches);
Serial.print("in, ");
Serial.print(cm);
Serial.print("cm, ");
//Serial.println();
delay(100);
// PWM SECTION:
{
if (cm >= 25 && cm <= 150)
{
x = ((cm/150.0)*255.0); // maintane car distance from the object,(25cm <= distance <= 150 cm) (0% < Duty cycle < 100%)
}
else if (cm <25)
{
x = 0; // STOP car!, Duty cycle = 0%
}
else
{
x = 254; // full speed, clear road, Duty cycle = 100%
}
analogWrite (pwmPin, x); // this pin is connected to a chip to drive the car motor.
Serial.print("X VALUES IS: ");
Serial.print(x);
Serial.println();
delay (20);
}
}
long microsecondsToInches(long microseconds)
{
// According to Parallax's datasheet for the PING))), there are
// 73.746 microseconds per inch (i.e. sound travels at 1130 feet per
// second). This gives the distance travelled by the ping, outbound
// and return, so we divide by 2 to get the distance of the obstacle.
// See: http://www.parallax.com/dl/docs/prod/acc/28015-PING-v1.3.pdf
return microseconds / 74 / 2;
}
long microsecondsToCentimeters(long microseconds)
{
// The speed of sound is 340 m/s or 29 microseconds per centimeter.
// The ping travels out and back, so to find the distance of the
// object we take half of the distance travelled.
return microseconds / 29 / 2;
}