The Machine That Goes Ping

A Cantus Firmus Generator for atmega328p (Arduino Nano)

About the project

This is an exercise project for the microcontroller programming course held during the summer semester of 2018 in the Physics Department of the Warsaw University. It was developed and tested on atmega 328p chip incorporated on Arduino Nano board. However, it can be easily ported to other hardware when appropriate hardware_XXX.h header is provided.

Cantus Firmus (lat: "Firmed Song") is a general name for a melody composed according to a set of rules consisting of passages and jumps. It was widely used in the middle ages, usually as the basis for polyphonic improvisation. Nowadays, it can be heard in sacral and monastic choral music.

The idea of the project is to create a generator of sinusoidal analog signal, which will randomly change the pitch to create a melody similar to Cantus Firmus. The only hardware requirement a mini jack socket connected to Arduino Nano's gnd and D9 pins and a low-pass filter to remove some artifact frequencies. In this configuration, standard headphones can be used to listen to the melody.

The application configures two hardware timers to create the signal: first one is used for PWM, which allows digital to analog conversion, the other one is used to regularly update the output analog signal, so the sine function is "drawn". The third timer is used to change the output frequency randomly but according to some rules.

Build guide

1. Configure the toolchain. Open the Makefile and change the variables CXX, OBJCOPY, AVRDUDE accordingly to your avr installation. Important: avr-g++ compiler version has to support C++14.
2. Execute:

make upload

Additional features

Additional features are provided for debugging purposes:

• Error modes (upload_with_error_modes target). Simple macros are used for debugging. When some forbidden state is reached (i.e. chunk of signal is requested for output before it's prepared), the device enters an ERROR mode. All interrupts are disabled, and main loop is stopped. The led on Arduino Nano board starts to flash regularly. Number of flashes in a sequence indicates the index of error state reached. This is disabled in default configuration for optimization.
• Test configuration (test and test_with_error_modes targets). Application can be run on any machine, with calls to hardware functions mocked by printing a log to stdout. Interrupts are not simulated yet in test configuration, so only the behavior of the main loop and initial configuration can be tested. This can be also used for unit tests, if the main.cc is edited accordingly.