Servo motor noise in analog input

i'm trying move servo motor according audio stream. noticed servo gets connected, there noise in analog read value. removed , connected a0 gnd, servo 5v, gnd , pin 9, uploaded below code , watched serial monitor. got noise in analog input average value of 30 , max of 40. if remove servo, flat 0 reading, expected. behavior expected servo , how prevent polluting analog inputs? tried adding 0.1uf , 10uf caps servo power pins of no use.

-antzy

code: [select]


#include <servo.h>

servo myservo;  // create servo object control servo

int pos = 0;    // variable store servo position
int sensorvalue;

void setup()
{
  serial.begin(9600);
  myservo.attach(9);  // attaches servo on pin 9 servo object
}

void loop()
{
  for(pos = 0; pos < 180; pos += 1)  // goes 0 degrees 180 degrees
  {                                  // in steps of 1 degree
    myservo.write(pos);              // tell servo go position in variable 'pos'

    serial.print("{");
    serial.print("input");
    serial.print(",t,");
    serial.print(getmaxval());
    serial.println("}");
 
  }
  for(pos = 180; pos>=1; pos-=1)     // goes 180 degrees 0 degrees
  {                               
    myservo.write(pos);              // tell servo go position in variable 'pos'

 
    // print out value read:
    serial.print("{");
    serial.print("input");
    serial.print(",t,");
    serial.print(getmaxval());
    serial.println("}");
  } 
}

int getmaxval()
{
  int maxval = 0;
  for(int i=0;i<100;i++)
  {
    sensorvalue = analogread(a0);
    if(sensorvalue > maxval)
      maxval = sensorvalue;
  }
 
  return maxval;
}


i tried powering servo seperate regulated 5v supply , induced noise in power supply lines. when drawing power arduino, possibly changing aref voltage causing noise in adc.

the mention of electrical noise due servo on internet find solution was:
http://letsmakerobots.com/node/12679
i tried putting caps across power , signal suggest didn't work.

i found grump mike's decoupling tutorial:
http://www.thebox.myzen.co.uk/tutorial/de-coupling.html
the capacitors-resistor option didn't work. have buy inductor , give try. has else ever  experienced problem before? couldn't find many mentions of on whole wide internet.

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