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Copyright and Licensing

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Readme.md is part of the ff-ad9833 project.

ff-ad9833 is an audio project for FlashForth and the AD9833

Copyright (C) 2021 Christopher Howard

SPDX-License-Identifier: GPL-3.0-or-later

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see https://www.gnu.org/licenses/.


This project contains FlashForth code for a hobby project to control a GY-9833-based audio module using an Arduino UNO. These are some blog posts regarding the project:


I have provided here a system for storing and playing single channel melodies, which I am calling `scores', using notes from three octaves of the equal temperament music scale.

I have thoughts also of providing in the future a module for outputting Audio FSK data communication.

The code should be helpful to those wanting to understand how to interact with the GY-9833 module, or the AD9833 IC, through FlashForth. I try to keep the code cleanly-documented and well-organized.


The GY-9833 is single channel, and by itself it does not have any capabilities for controlling volume, including attack or release volume evelopes. So it is less than ideal for creating video game music or realistic instrument sounds. Nevertheless, it generates a clean sine wave which is pleasant to hear and which is suitable for some applications.

The system I have provided for playing scores has imprecise note duration on the scale of up to a few milliseconds per note. Consequently it might not keep synchronized tempo with other machine music generation systems, including another chip running this same system.

Code documentation

Each Forth code file has the following documentation in comments:

  1. The title of the file
  2. A copyright and license header
  3. A description of the purpose of the file
  4. A list of public words, i.e., words meant to be used outside of the module itself
  5. The code is divided into sections, each containing a section description.
  6. Each dictionary word, not including words like constants and variables, contains a brief Forth-style stack effect description.


  • An Arduino UNO or other board with 328P MC
  • MC should be running FlashForth 5
  • You will need the doloop.fs file, available in the avr/forth directory of the FlashForth source code. It is not included in the ff-ad9833 source since it is part of the FlashForth system.
  • GY-9833 module driving a speaker. An inexpensive project PCB, which amplifies output from the GY-9833, can be ordered through a link at the blog post referenced above. Other ad9833-based modules should work also, but be aware the code assumes a 25Mhz clock-rate in the frequency-register calculations
  • The code assumes the fsync pin is PD4 (Arduino DP4) but this can be modified in the ad9833.fs file parameter constants.


After setting up a FlashForth shell connection, run these commands in the shell.

In FlashForth, you only need to compile (#send) the code once, and then you can run the compiled words later, even after resetting the microcontroller. For more information about FlashForth, visit

FlashForth Web Site

Core words and definitions for controlling the ad9833

#send doloop
#send util
#send 328p
#send ad9833

Musical notes and scores of notes

#send notes
#send score
#send demo-melodies

Running Demos

After setting up a FlashForth shell connection, enter the words command and look for words to execute which are prefixed with demo-.