Sound and Piezo Buzzers

Sound and Piezo Buzzers

Quick Review: Sound Frequencies

• Sound is created by vibrations in air pressure (sound waves)
• Commonly we measure the amplitude (volume) and the frequency (perceived pitch)

Piezo Buzzer

Piezo Buzzer

• Uses magnetic coil to vibrate a metal disc to produce sound
• Control the pitch by a form of pulse width modulation (PWM)

Uses of piezo buzzers

• Buzzer are small and cost-effective
• Can be used for alarms, games, toys
• Can produce tones and simulate single notes

Limitations of Buzzer

• Frequency
  • Human hearing is roughly 20 Hz to 20,000 KHz
  • Hertz (Hz) is cycles per second
  • Piezo buzzer operates up to 2.048 KHz
• Sound Quality
  • Only generate tones through square waves

Connecting Buzzers

Connecting Buzzers

• Buzzers are polarized so look for the +
• Negative pin to gnd and positive pin to Photon 2 output

Producing Sound

Syntax

tone(<<PIN>>, <<FREQUENCY>>);		// will play tone indefinitely
tone(<<PIN>>, <<FREQUENCY>>, <<DURATION>>);

• tone() generates a square wave using PWM (50% duty cycle)

• pin is connected the speaker

• frequency is sound frequency in Hz (20Hz to 20KHz)

• duration is the length of tone in milliseconds

Producing Sound

Example

tone(D6, 500, 1000);	// play 500Hz tone for 1000ms (1 sec)
tone(D2, 2000, 3000);	// play 2KHz tone for 3000 ms (3 sec)
tone(D2, 1000, 0);		// play 1KHz tone (don't stop)

A Note on Photon 2 and tone()

• tone() requires a pin that supports PWM
• Only certain pins support PWM
  • D1 (SCL or A4)
  • A2
  • A5
  • MISO (D16)
  • MOSI (D15)
• All PWM pins on the Photon 2 are assigned to the same timer, meaning you can only generate ONE frequency at a time. In other words, you cannot play different notes with different buzzers at the same time.

Stopping Sound

Syntax

noTone(<<PIN>>);

• To stop a continuous tone or stop tone before duration is over

A Note about Tone and Blocking

• tone() is non-blocking (meaning it doesn’t cause delays or interfere with other Photon 2 actions)
• This means the Photon 2 will not wait for one tone() to finish before playing the next. For example, in the code below, even though the first tone has a duration of 1 sec, the second tone will start immediately, meaning you will hear the second tone

tone(D6, 500, 1000);	
tone(D2, 2000, 3000);	

• In order hear a tone for certain length of time, we either need to use a millis() timer or delay()

Optional: Controlling Volume

Optional: Controlling Volume

• All tones will be at the same volume since Photon 2 can change only frequency (not amplitude)
• To control volume, connect a potentiometer between negative and gnd
• Potentiometer acts a current limit resistor to control volume

Playing Melodies

• Musical notes can represented as constants
• Add this file (pitches.h) to your src folder and then add #include "pitches.h" to your sketch
• You can then refer to music notes in the following manner

tone(D2, NOTE_C4, 1000);  // play the note "middle C"	

Finding Notes of Popular Songs

• Notes for some popular songs (note that the format for playing notes is different in this code, but you can still extract the notes and duration from these examples)
• MIDI to C converter allows you convert a MIDI file directly into

References

• Images created with Fritzing
• Pixabay
• Sparkfun
• Neuton Foo