void setup() {
	Serial.begin(115200);

	pinMode(LEFT_MOTOR_PIN, OUTPUT);
	pinMode(RIGHT_MOTOR_PIN, OUTPUT);
	pinMode(LEFT_MOTOR_DIRECT_PIN, OUTPUT);
	pinMode(RIGHT_MOTOR_DIRECT_PIN, OUTPUT);

	for(byte i = LOW_CHANNEL; i <= NUM_CHANNELS; i++) {
		pinMode(channels[i], INPUT);
	}

	enableInterrupts();

	delay(2000);
}

void enableInterrupts() {
	for(byte i = 0; i <= NUM_CHANNELS; i++) {
		byte pin = channels[i];
		
		*digitalPinToPCMSK(pin) |= bit (digitalPinToPCMSKbit(pin));  // enable pin
		PCIFR |= bit (digitalPinToPCICRbit(pin)); // clear any outstanding interrupt
		PCICR |= bit (digitalPinToPCICRbit(pin)); // enable interrupt for the group 
	}
}

// handle pin change interrupt for D8 to D13 here
ISR (PCINT0_vect) {
	readPins();
}