An ATMEGA328-P chip is used with a toggle switch attached to pin 8 and a momentary switch attached to pin 9. My objective is to send the following information over serial:

1. The status of pin 8, every second.
2. Count the number of presses of pin 9, sending the value as the counter increments

I understand that to achieve point 2 I will need to utilise interrupts, but I have become stuck in the way I am trying to use them.

I am familiar with the following code's simple style:

1. Within the loop...
2. Poll the status of the input
3. Send status over serial

Code A:

const int SWITCH_1 = 8;
const int READ_INTERVAL = 1000;
int val_s1 = 0;
void setup() {
 Serial.begin(9600);
 pinMode(LED_BUILTIN, OUTPUT);
 pinMode(SWITCH_1, INPUT);
 digitalWrite(S1, HIGH);
}
void loop() {
 val_s1 = digitalRead(SWITCH_1);
 Serial.print("S1:");
 Serial.print(val_s1);
 Serial.print("\n");
 digitalWrite(LED_BUILTIN, HIGH);
 delay(10);
 digitalWrite(LED_BUILTIN, LOW);
 delay(READ_INTERVAL);
}

When introducing the concept of interrupts, I have tried to retain the simplistic style of code A for testing purposes. The next snipped attempts to achieve the following:

1. Attach an interrupt to pin 9 when the voltage rises
2. No need for loop function (?)
3. Within interrupt callback function...
4. Increment the counter
5. Send the counter value over serial

Code B:

void c1_rise();
const int COUNTER_1 = 9;
const int READ_INTERVAL = 1000;
volatile int val_c1 = 0;
void setup() {
 Serial.begin(9600);
 pinMode(LED_BUILTIN, OUTPUT);
 pinMode(COUNTER_1, INPUT_PULLUP);
 attachInterrupt(COUNTER_1, c1_rise, RISING);
}
void loop() {
}
void c1_rise() {
 val_c1 ++;
 Serial.print("C1:");
 Serial.print(val_c1);
 Serial.print("\n");
}

I've tried to learn where I'm going wrong, but I have become stuck and have decided to ask my questions here.

• Observation: I expect to see some data sent over serial when the button is pressed, but actually nothing observable happens.
• Problem 1: This might be because the interrupt isn't being attached at all.
• Problem 2: This might be because I misunderstand the limitations of interrupt callback functions.

While trying to solve problem 1, Arduino documentation implies that to use the attachInterrupt function, parameter 1 must be an interrupt, from digitalPinToInterrupt, but if I use that function I receive the following error message: error: ‘digitalPinToInterrupt’ was not declared in this scope.

From reading up about how interrupts behave, I found problem 2: it seems that even though I have declared the integer as volatile, using Serial from within a callback function isn't allowed. This is the limit of my knowledge currently, I hope that someone can help me out.