music

Music Example

In this example we will see how to play some simple music with the micro:bit and a piezo buzzer.

In the Analog Out we said that the analog output was actually a Pulse Width Modulation (PWM) signal. When a piezo buzzer is connected to a PWM a note is produced, changing the frequency of the PWM signal means changing the note that the buzzer will play.

Wiring Diagram

For this example we simply connect a piezo buzzer to pin 0 and ground.

Extra hardware:

• A breadboard
• A piezo buzzer

Wiring:

Code

The package MicroBit.Music provides different ways to play music. We are going to use the procedure that plays a melody. A Melody is an array of Note, each Note is made of a pitch and a duration in milliseconds. This package also provides declaration of pitches for the chromatic scale (e.g C4, GS5).

So we declare our little melody like so:

   My_Little_Melody : constant MicroBit.Music.Melody :=
     ((C4,   400),
      (G3,   800),
      (B3,   400),
      (Rest, 400),
      (A3,   400),
      (G3,   400));

The melody is constant because we are not going to change it during the execution of the program.

Then we simply have to call the procedure Play of the package MicroBit.Music.

   procedure Play (Pin : Pin_Id; M : Melody)
     with Pre => Supports (Pin, Analog);

Arguments:

• Pin : The id of the pin that the melody will play on
• M : The melody that we want to play

Precondition:

The procedure Play has a precondition that the pin must support analog IO.

Here is the code:

with MicroBit.Music; use MicroBit.Music;

procedure Main is

   My_Little_Melody : constant MicroBit.Music.Melody :=
     ((C4,   400),
      (G3,   800),
      (B3,   400),
      (Rest, 400),
      (A3,   400),
      (G3,   400));
begin

   --  Loop forever
   loop

      --  Play the little melody on pin 0
      MicroBit.Music.Play (0, My_Little_Melody);
   end loop;
end Main;