/*PWM signal on most pins is approximately 490 Hz
On the Uno and similar boards, pins 5 and 6
have a frequency of approximately 980 Hz
brightness1, brightness2 = from 0 to 255
So make eqution to calculate needed frequency
255 - 980Hz
X   - 650/850
X1 = 650 Hz ~ 169
X2 = 850 Hz ~ 221*/

//LED are connected to:
const int ledPin1 = 5;
const int ledPin2 = 6;
byte brightness1 = 169, brightness2 = 221;
void setup()
{
  // initialize the ledPin as an output:
  pinMode(ledPin1, OUTPUT);
  pinMode(ledPin2, OUTPUT);
}

void loop() {
    // set the brightness of the LED:
    analogWrite(ledPin1, brightness1);
    analogWrite(ledPin2, brightness2);

}