Moving servo and read ultrasonic at the same time

Projects Programming
1

Hi I'm trying to combine the Servo Knob example with Ultrasonic sensor.

Here's my sketch

#include "Ultrasonic.h"
Ultrasonic sonar(2,3);
int sonarPreviousMillis = 0;
unsigned long sonarCurrentMillis;
int sonarInterval = 500;
int range;
#include <Servo.h> 
 
Servo myservo;  // create servo object to control a servo 
int potpin = 0;  // analog pin used to connect the potentiometer
int servoVal;    // variable to read the value from the analog pin 
int servoPreviousMillis = 0;
unsigned long servoCurrentMillis;
int servoInterval = 5;

void setup() 
{ 
  Serial.begin(9600);
  myservo.attach(9);  // attaches the servo on pin 9 to the servo object 
} 
 
void loop() 
{ 
  head();
  runSonar();
} 

void head(){
  servoCurrentMillis = millis();
  if(servoCurrentMillis - servoPreviousMillis > servoInterval) {
    servoPreviousMillis = servoCurrentMillis;
    servoVal = analogRead(potpin);            // reads the value of the potentiometer (value between 0 and 1023) 
    servoVal = map(servoVal, 0, 1023, 0, 179);     // scale it to use it with the servo (value between 0 and 180) 
    myservo.write(servoVal);
  }
}
void runSonar(){
  sonarCurrentMillis = millis();
  if(sonarCurrentMillis - sonarPreviousMillis > sonarInterval) {
    sonarPreviousMillis = sonarCurrentMillis; 
    range = sonar.Ranging(CM);
    if (range == 0){
       Serial.println("too far");  
    }else{
       Serial.print(sonar.Ranging(CM));
       Serial.println("cm");
    }  
  }
}

I would like to know if there is any better way to do such concurrent operations.
It seems the above sketch's Serial output got faster then 500ms when the sketch ran for a while, and the servo movement is a bit sloppy afterwards.

2

It seems the above sketch's Serial output got faster then 500ms when the sketch ran for a while, and the servo movement is a bit sloppy afterwards.

Why not print out the servoCurrentMillis() value. Then, you won't have to use words like "seems to". You can use "does" (or "does not") instead.

3

Hi Paul

Yea I did tried to print the values, the problem is the intervals were really 500ms at the beginning when the sketch runs.
After a random period, say 10 seconds, the println started to get strange the the readings are updating in a rate like 10ms on the Serial reader.

When I try to wave in front of the ultrasonic sensor, the distance reading changes, then suddenly the println rate is back to normal.

Will the serial reader messages be held up in a queue and got blocked by something?

4

Serial.print etc one the earlier Arduino 022 will BLOCK. That is, the program will not continue until the last character is sent.
On the Arduino 1.0 all serial outputs put in a buffer and the interrupts will empty the output buffer as fast as possible. Thus a simple Seril.print or two will not block, but if you fill the buffer (64 characters) faster then it can empty, then the Serial.print will BLOCK for a while.

You can partially test if this is happening for you by increasing or decreasing the baud rate.