Trouble with speaker

Forum 2005-2010 (read only) Hardware Interfacing
#1

hi there. i have a small Peizo speaker that i can drive from the PWM pins on my arduino, i can get it working fine with the melody sketch but i am having trouble understanding it to an extent.

what i want to be able to do is play a short sequence of notes when some thing happens, using an IF statement ideally. but all i can seem to do is change the pulse width and not the frequency:

analogWrite(spkrpin, 220) etc...

I have tried to abstract something from the melody sketch but i dont really understand it!

#2

analogWrite uses a fixed frequency, but varies the mark:space ratio, i.e. the ratio of the time the waveform is high to the time the waveform is low.

If you look at the example sketch, you’ll see that it doesn’t use analogWrite, but instead uses explicit “delayMicroseconds” calls.

#define speakerPin 9
#define switchPin   3   //whatever

int length = 15; // the number of notes
char notes[] = "ccggaagffeeddc "; // a space represents a rest
int beats[] = { 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 2, 4 };
int tempo = 300;

void playTone(int tone, int duration) {
  for (long i = 0; i < duration * 1000L; i += tone * 2) {
    digitalWrite(speakerPin, HIGH);
    delayMicroseconds(tone);
    digitalWrite(speakerPin, LOW);
    delayMicroseconds(tone);
  }
}

void playNote(char note, int duration) {
  char names[] = { 'c', 'd', 'e', 'f', 'g', 'a', 'b', 'C' };
  int tones[] = { 1915, 1700, 1519, 1432, 1275, 1136, 1014, 956 };

  // play the tone corresponding to the note name
  for (int i = 0; i < 8; i++) {
    if (names[i] == note) {
      playTone(tones[i], duration);
    }
  }
}

void setup() {
  pinMode(speakerPin, OUTPUT);
  pinMode(switchPin, INPUT);
  digitalWrite (switchPin, HIGH);  //enable the pull-ups
  // switch is normally-open, connected between switchPin and Gnd
}

void loop() {

if (LOW == digitalRead (switchPin) ) {
  for (int i = 0; i < length; i++) {
    if (notes[i] == ' ') {
      delay(beats[i] * tempo); // rest
    } else {
      playNote(notes[i], beats[i] * tempo);
    }

    // pause between notes
    delay(tempo / 2); 
  }
}
}

Seems a likely starting point. (uncompiled, unchecked)

#3

thats exactly what i thought. I am still unsure as to how i can make it output a tone though. once i have that i can work out the code i need.

#4

Have a look at this :- http://www.arduino.cc/playground/Main/InterfacingWithHardware#audio_tutorial

#5