Help with smoothing

Forum 2005-2010 (read only) Software Syntax & Programs
1

I've got a system setup that reads a temp sensor, and depending on temp sensor readings it will move a servo. The problem I'm having is that the servo gets very jittery. How can I work the smoothing example into my code? I see the example just writes to serial output. Here is my code for my control:

// Controlling a servo position using a temperature sensor 
// by Michal Rinott <http://people.interaction-ivrea.it/m.rinott> 
// edited 5-12-2010 by Will Lyon to include base setting for servo if voltage not detected on pin 7

#include <Servo.h> 
#define CONTROL 7

Servo myservo;  // create servo object to control a servo 
 
int temps = 0;  // analog pin used to connect the temp sensor
int val;        // variable to read the value from the analog pin
 
void setup() 
{ 
  pinMode (CONTROL, INPUT);       // sets the control pin to input
  myservo.attach(9);              // attaches the servo on pin 9 to the servo object
  digitalWrite(CONTROL, LOW);     // ensure internal pullup resistor is disabled.

} 
 
void loop()   
{
  val = digitalRead(CONTROL);         //read input of pin 7 and store it
  if (val == HIGH){                   // reads whether or not 5v is present on pin 7, if 5v present, continue:
  val = analogRead(temps);            // reads the value of the temp sensor (value between 0 and 1023) 
  val = map(val, 350, 700, 75, 105);  // scale it to use it with the servo (value between 0 and 180) 
  myservo.write(val);                 // sets the servo position according to the scaled value 
  delay(25);                          // waits for the servo to get there 
} else {
  if (val == LOW);                    // if no voltage present on pin 7, continue
  myservo.write(50);                  //sets servo position to 50 if no voltage is detected on pin 7
}
delay(25);        // waits for the servo to get there

}

Here is a link to my projects:
Fritzing setup: Arduino Temperature-based servo control
Worklog @ TheBestCaseScenario.com: Project: Tempest SXR

Thanks in advance for the help!

2

Just a simple rolling average - take off, say one eighth of the sum, and add in one eighth of the new reading.

Hint:

  if (val == HIGH){} else {
...
...
  if (val == LOW);

if val isn't HIGH, there's no need to test to see if it's low.

3

take, say one eighth of the sum, and add in one eighth of the new reading.

Could you give an example of the code?

I mean, for a moving average don't you, somehow, have to subtract the oldest value from the sum and add the newest value?

That is: for a filter of length eight don't you need to keep the most recent eight samples in an array or some such thing?

Regards,

Dave

4 
sum = (sum - (sum / 8)) + (analogRead (pin) / 8);

Or yes, you could maintain a history in an array.

5

Thank you.

Regards,

Dave