Firmware for the ATmega 328p that allows you to play progammable music with a piezo buzzer
The goal of this lab assignment was to generate music using piezo buzzers and bare-bones C++ (no arduino libraries)
The firmware is relatively straightforward:
- Configure a built-in 8-bit timer to count milliseconds
- Configure a built-in 16-bit timer to generate a square wave to send to the buzzer to make note frequencies
- Iterate through two arrays
- One array holds timing information, telling the program when to move to the next array element
- The other array holds Compare Match Values for the 16-bit timer. This array changes the note being played
To stop sound for rests, indicated by 0 in the note array, and to allow for the same note to be played multiple times in a row, the program disconnects the square wave output at the end of each note for a few milliseconds, only re-enabling the output at the next non-0 note.
The firmware is simple to code, but it comes with a drawback: it relies on specifically formatted arrays to load onto the microcontroller.
To overcome this issue and make it easy to program multiple different songs, I wrote a python program that translates from an easy-to-write text file to the specific C++ arrays for the firmware. The ultimate goal was to make it easy to transcribe sheet music into this system.
First, create a .txt file. The very first line must be an integer that specifies the BPM Subsequent lines can be empty, contain a comment, or contain note information. Whitespace and comments make it easy to organize the text file for future reference.
Note information should be formatted like [Note] [Number_of_Beats]
[Note] should be a note's name, an optional sharp, and the octave
e.g. E4, Fs3, c#5, DS4, X, REST
The note is not case sensitive, and sharps can be denoted by 's' or '#'
X and REST denote a rest / pause in the music
This program, due to the 16-bit timer, supports octaves 3 - 8
[Number_of_Beats] should be a floating point number indicating how long to hold the note.
The note and its timing should be on the same line, separated by a space.
Once you have your text file, use MusicTranslator.py
- Replace
song_file = "Tetris.txt"withsong_file = "[your_text_file]" - Run MusicTranslator.py
- The results will show up in a new file in the same directory. Copy the array definitions from this text file into the C++ firmware
The translator will create a text file with C++ array and variable declarations. Copy these over the existing declarations in the firmware, then upload the firmware to the board. If the circuit for the ATmega328p is setup correctly (see the header in the firmware), the board should now be playing your song!
Input file: Tetris.txt
130
// Beginning of song
E5 1
B4 .5
C5 .5
D5 1
C5 .5
B4 .5
A4 1
A4 .5
C5 .5
E5 1
D5 .5
C5 .5
B4 1.5
C5 .5
D5 1
E5 1
C5 1
A4 1
A4 1
X 1
... (rest of file not shown)
Output file: Tetris_arrays2.txt
const uint16_t notes[] = {12134, 16198, 15289, 13620, 15289, 16198, 18181, 18181, 15289, 12134, 13620, 15289, 16198, 15289, 13620, 12134, 15289, 18181, 18181, 0, 0, 13620, 11453, 9090, 10204, 11453, 12134, 15289, 12134, 13620, 15289, 16198, 15289, 13620, 12134, 15289, 18181, 18181, 0, 12134, 15289, 13620, 16198, 15289, 18181, 19263, 12134, 15289, 13620, 16198, 15289, 12134, 9090, 9090, 9631};
const int timing_ms[] = {462, 231, 231, 462, 231, 231, 462, 231, 231, 462, 231, 231, 692, 231, 462, 462, 462, 462, 462, 462, 231, 462, 231, 462, 231, 231, 692, 231, 462, 231, 231, 692, 231, 462, 462, 462, 462, 462, 462, 923, 923, 923, 923, 923, 923, 1846, 923, 923, 923, 923, 462, 462, 462, 462, 1846};
int last_note = 55;
Video of the circuit playing "Attack of the Killer Queen," a song by Toby Fox, Lena Raine, and Marcy Nabors.
This tune has 451 notes, which was only reasonable to program thanks to the python music translator.
The biggest drawback to this approach is the need to store every note with an integer and a 16-bit integer, which takes up a lot of space. It would probably be better to store each 16-bit value for the notes once as a constant, and use an 8-bit number to represent which note to select.