analogWrite mosfet problem

Question

i have a custom atmega328p board which have connected to pin 9 the gate of a MOSFET. If i run a simple sketch like:

void setup() {

}
void loop() {
  analogWrite(9,70);
}

The motor connected to the mosfet works just fine, from 70pwm to 255pwm.

On the other sketch i'm receiving serial data from an android app via bluetooth. Ive 2 Servo motors and a DC motor connected to the mosfet. The 2 servos works like expected, the DC motor doesn't spin unless i use a 255pwm.

void loop() {
  if(Serial.available() > 0){     
      state = Serial.read();  
  }
  if (state == 'S') {
      servoONE.write(90);
      servoTWO.write(90);
      analogWrite(MOSFET,MOSFET_LOW);
  }
  else if (state == 'F') {
      analogWrite(9,70);
      servoONE.write(90);
      servoTWO.write(90);
  }
  else if (state == 'L') {
      servoONE.write(MAX_SERVO);
      servoTWO.write(MIN_SERVO);
  }
  else if (state == 'R') {
      servoONE.write(MIN_SERVO);
      servoTWO.write(MAX_SERVO);
  }
  else if (state == 'Q') {
      analogWrite(MOSFET,MOSFET_HIGH);
      servoONE.write(MAX_SERVO);
      servoTWO.write(MIN_SERVO);
  }
  else if (state == 'E') {
      analogWrite(MOSFET,MOSFET_HIGH);
      servoONE.write(MIN_SERVO);
      servoTWO.write(MAX_SERVO);
  }
}

Do you know why the same motor works on the first sketch with any pwm above 70 and on the second sketch it only works at 255?

Answer 1

You have a timer conflict.

Pin 9 is OC1A which is the Output Compare Channel A pin of Timer 1. However the Servo.h library also uses timer 1.

So you can't use servos and still use pins 9 (OC1A) and 10 (OC1B) as PWM.

However, you can still use pins 3, 5, 6 and 11 as PWM since they are on other timers.