#define GAP_DELAY 1000
#define DWELL 3
#define SPARK_DELAY 20
#define C1 2
#define C2 5
#define C3 18
#define C4 19

// int  rpm_table = [4.5, 4, 3.5, 3, 2.5]; // corresponding dwell to rpm 1000, 2000, 3000, 4000, 5000

void setup() {
  pinMode(C1, OUTPUT);
  pinMode(C2, OUTPUT);
  pinMode(C3, OUTPUT);
  pinMode(C4, OUTPUT);
}

void loop() {
  
    digitalWrite(C1, HIGH);
    delay(DWELL);
    digitalWrite(C1, LOW);
    delay(SPARK_DELAY);

    digitalWrite(C2, HIGH);
    delay(DWELL);
    digitalWrite(C2, LOW);
    delay(SPARK_DELAY);

    digitalWrite(C3, HIGH);
    delay(DWELL);
    digitalWrite(C3, LOW);
    delay(SPARK_DELAY);

    digitalWrite(C4, HIGH);
    delay(DWELL);
    digitalWrite(C4, LOW);
    delay(SPARK_DELAY);

    delay(GAP_DELAY);
}