Several years ago, Jesper Hansen published a design for an AVR based mini-DDS generator. This project uses an AVR microcontroller and a simple resistor based DAC to generate various waveforms (sine, sawtooth, triangle, square) using a DDS software technique. Jesper also published a small Windows based program to control the generator, for example to change the frequency or waveform. Take a look at Jesper's project.

Since the Dutchtronix AVR Oscilloscope Clock hardware is well suited for this application, I ported it. It is now included as one of the standard applications in the V3.5a firmware.

The Dutchtronix AVR hardware uses a separate DAC IC, not a set of resistors. This results in very precise dots, good when creating a sharp image like the Clock, but not so good for this Function Generator. As a result, the waveforms are more "blocky". It also takes more steps to do one cycle in the DDS generation (13 cycles as opposed to 9 cycles in the original).

Finally, due to the tight DDS generation loop, it is not possible to poll the on-board tactile switches for user input. Only the serial input can be used since it can generate an interrupt. Therefore the AVR Clock needs to be connected to a Windows computer where you can use the ddscontrol program (download it here). Such a connection will require the installation of an RS-232 Level Conversion Circuit.

Please remember that this is a design from Jesper Hansen and he is the owner of all the rights to this project.

Instructions:

Start the downloaded ddscontrol.exe program. Right click the title bar to configure it.

You should see a waveform on your oscilloscope. You can change the shape and set the frequency using ddscontrol. Or you can incrementally increase or decrease using the arrows:

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