Tone and attachInterrupt

Using Arduino Programming Questions
1

I tried to make a sketch with attachInterrupt and tone methods.

void setup() {
    Serial.begin(57600);
    Serial.println("Start");

    attachInterrupt(0, changed, CHANGE);
    tone(6, 1000);

}

This sketch outputted no tone unless I removed the attachinterrupt. I thought that external interrupts were completely separate from timer interrupts. What is happening?

2

orangeLearner:
I thought that external interrupts were completely separate from timer interrupts.

They are.

What is happening?

You forgot to post your code. You also forgot to include a description of the interrupt rate.

3

I apologize. Here is my full code:

/* Prints the time in ms between interrupts. */
 
volatile unsigned long lastInterrupt = 0;

void setup() {
    Serial.begin(57600);
    Serial.println("Start");
    attachInterrupt(0, changed, CHANGE);

}

void loop() {
    tone(6, 1000);
    delay(2000);
    noTone(6);    
    delay(2000);
}
void changed(){
    Serial.print(!digitalRead(2));
    Serial.print(": ");
    Serial.println(micros() - lastInterrupt);
    lastInterrupt = micros();
}

And here is the circuit. Originally pin 6 was connected to the data in of this RF transmitter and pin 2 was connected to the data out of the data out of this receiver, but when that failed to produce any interrupts at all, I switched to this circuit:

When the yellow wire is disconnected, it will output a tone for two seconds, delay, then repeat like expected. When I connect the yellow wire, at the next tone output, the TX light blinks and the sketch stops even if I disconnect the yellow wire again. What could be happening?

4

It's a mistake to do Serial.print in an interrupt routine. That relies on interrupts, which are disabled.

5

Is there any sound output? Ticking noise?

The sequence of events...

The tone timer interrupt fires. The timer interrupt service routine adjusts the tone output pin (pin 6) and returns.

Pin 2 was toggled (because tone toggle it) so the INT0 interrupt fires ultimately resulting in your function (changed) being called. Your function does several things that use a moderate amount of CPU time (digitalRead, micros twice, converting an unsigned long to text, buffer data for serial output).

In order to generate a 1000 Hz tone, the tone timer interrupt service routine has to run every 1/(2*1000)*1000000 = 500 microseconds. Your function (changed) is very likely taking much longer than 500 microseconds to run. The "overrun" prevents tone from working correctly.

Originally pin 6 was connected to the data in of this RF transmitter and pin 2 was connected to the data out of the data out of this receiver,

Why? SoftwareSerial (NewSoftSerial) should work reasonably well.

6