int TRIAC = 6;
int speed_val=0;
void setup()
{
  Serial.begin(9600);
  pinMode(A0,INPUT);
  pinMode(TRIAC, OUTPUT);
  attachInterrupt(digitalPinToInterrupt(3), zero_crossing, CHANGE);
}
void zero_crossing()
{
  //Serial.println(".");
  int chop_time = (200*speed_val);
  delayMicroseconds(chop_time);
  digitalWrite(TRIAC, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIAC, LOW);
}
void loop()
{
    int pot=analogRead(A0);
    if(pot>650){pot=660;}
    int data1 = map(pot, 0, 660,30,10);
    speed_val=data1;
    Serial.println(data1);
}