Generates a square wave of the specified frequency (and 50% duty cycle) on a pin. A duration can be specified, otherwise the wave continues until a call to noTone(). The pin can be connected to a piezo buzzer or other speaker to play tones.
Only one tone can be generated at a time. If a tone is already playing on a different pin, the call to tone() will have no effect. If the tone is playing on the same pin, the call will set its frequency.
Use of the tone() function will interfere with PWM output on pins 3 and 11 (on boards other than the Mega).
NOTE: if you want to play different pitches on multiple pins, you need to call noTone() on one pin before calling tone() on the next pin.
tone(pin, frequency, duration)
pin: the pin on which to generate the tone
frequency: the frequency of the tone in hertz - unsigned int
duration: the duration of the tone in milliseconds (optional) - unsigned long