Ada for micro:bit Part 8: Music to my ears

by Fabien Chouteau – Nov 03, 2020

Welcome to the Ada for micro:bit series where we look at simple examples to learn how to program the BBC micro:bit with Ada.

If you haven't already, please follow the instructions in Part 1 to setup your development environment.

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

In the analog output example 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 will need a couple of extra parts:

A breadboard
A piezo buzzer
A couple of wires to connect them

Interface

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));

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 full code of the example:

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;

Following the instructions of Part 1 you can open this example (Ada_Drivers_Library-master\examples\MicroBit\music\music.gpr), compile and program it on your micro:bit.

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About Fabien Chouteau

Fabien joined AdaCore in 2010 after his engineering degree at the EPITA (Paris). He is involved in real-time, embedded and hardware simulation technology. Maker/DIYer in his spare time, his projects include electronics, music and woodworking.