Arduino Mega External Interrupts

Using Arduino Project Guidance
1

Hello! I am in the process of making an RC craft, and have successfully used a Mega 2560, with pins 2 and 3 for interrupts.

The Mega 2560 is capable of 6 external interrupts, which are 0-5 on pins 2, 3, 21, 20, 19, 18 respectively. However I cannot seem to find these last 4 pins. I have pin 2, and 3 working quite well however. Some schematics led me to believe Pin 18 for example is Analog input 4.

Any help? Thanks.. here is my code so far. Throttle and Aileron give numbers but elevator stays at 0 and is not called.. the jumper for the elevator is currently plugged into analog in 4

#include <Servo.h>


volatile unsigned long timer_start;
volatile int last_interrupt_time;
volatile int throttle = 0;
volatile int rudder = 0;
volatile int elevator = 0;
volatile int aileron = 0;
volatile int mode = 0;

const int aileronCH = 0; //pin 2
const int throttleCH = 1; //pin 3
const int elevatorCH = 5; //pin 18
const int rudderCH = 4; //pin 19
const int modeCH = 3; // 20

const int motorOnePIN = 8;

Servo motorOne;

void setup(){
  Serial.begin(9600);
  attachInterrupt(throttleCH, calcThrottle, CHANGE);
  attachInterrupt(aileronCH, calcAileron, CHANGE);
  attachInterrupt(elevatorCH, calcElevator, CHANGE);
  //attachInterrupt(rudderCH, calcRudder, CHANGE);
  //attachInterrupt(modeCH, calcMode, CHANGE);
  motorOne.attach(motorOnePIN);
}

void loop(){
  Serial.println("----");
  Serial.println(throttle);
  Serial.println(aileron);
  Serial.println(elevator);
  
  delay(200);
}


void calcThrottle()
{
 last_interrupt_time = micros();
 if(digitalRead(3) == HIGH){
        timer_start = micros();
    }else{
        if(timer_start > 0){
            throttle = ((volatile int)micros() - timer_start);
            timer_start = 0;
        }
    }
}
void calcAileron()
{
 last_interrupt_time = micros();
 if(digitalRead(2) == HIGH){
        timer_start = micros();
    }else{
        if(timer_start > 0){
            aileron = ((volatile int)micros() - timer_start);
            timer_start = 0;
        }
    }
}
void calcElevator()
{
 last_interrupt_time = micros();
 if(digitalRead(18) == HIGH){
        timer_start = micros();
    }else{
        if(timer_start > 0){
            elevator = ((volatile int)micros() - timer_start);
            timer_start = 0;
        }
    }
}
2

On the Mega are the digital pins not numbered right there on the board? That's how it is on mine anyway.

3

Here's a picture with the numbers on the board.

4

Yes, but where are pins 18, 19, 20 and 21?

5

In the picture they're on the top side of the board, close to the right end of the row of pins. The ones that say 18, 19, 20, and 21 next to them.

Am I missing something here? Why is this hard to figure out?

6

Dope. I am such an idiot.. sorry.