My DIY Journey: Building an AD9912 DDS Synthesizer with Arduino and a Custom Library

In the realm of RF and electronics hacking, a precise, agile, and controllable signal source is the holy grail. While there are many ways to generate frequencies, Direct Digital Synthesis (DDS) offers unparalleled precision and speed. That's why I chose the powerful Analog Devices AD9912 for my next project: a versatile DDS synthesizer controlled by an Arduino and managed directly from my PC.

This post documents my journey, including the hardware setup, the software challenges that led me to fork an existing library, and the final implementation that ties it all together with a simple serial interface.

My completed AD9912 synthesizer setup in action.

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The Core Components: AD9912 + Arduino

Why the AD9912?

The AD9912 is a beast of a DDS chip. It features: - A 1 GSPS internal clock - A 14-bit digital-to-analog converter (DAC) - The ability to generate signals up to 400 MHz with incredible frequency resolution.

This level of performance makes it perfect for everything from creating a variable frequency oscillator (VFO) for a ham radio project to building custom test equipment.

The Brains: An Arduino

For the controller, I went with an Arduino (you can use an Uno, Nano, or any other compatible board). Its simplicity, extensive community support, and straightforward SPI implementation made it the ideal choice to interface with the AD9912.

The Hardware: Connecting Everything via SPI

The communication between the Arduino and the AD9912 happens over the Serial Peripheral Interface (SPI) bus. This is a fast, synchronous protocol perfect for sending configuration data to the DDS.

The wiring is pretty standard for an SPI device:

• MOSI (Master Out, Slave In): Arduino sends data to the AD9912.
• MISO (Master In, Slave Out): AD9912 sends data back (useful for reading registers).
• SCK (Serial Clock): The clock signal that synchronizes the data transfer.
• CS (Chip Select): A dedicated pin to tell the AD9912 to listen for commands.

I designed a simple PCB to house the AD9912 and its supporting components, including clean power supplies and an output filter, to ensure the best possible signal integrity.

The essential SPI connections between the microcontroller and the DDS.

The Software: Why I Forked a Library

Once the hardware was wired, I needed software to control it. I found some existing Arduino libraries for Analog Devices DDS chips, but none of them quite fit my needs. Some were overly complex, while others lacked the specific functions I wanted to implement for easy serial control.

This is where the power of open-source shines. Instead of starting from scratch, I forked an existing AD9912 library on GitHub.

Forking allowed me to:

1. Build on a solid foundation: I didn't have to write the low-level SPI communication and register-writing functions myself.
2. Customize the API: I streamlined the interface, creating simple functions like setFrequency(long freq) that were easy to call.
3. Optimize for my use case: I stripped out features I didn't need and focused on making the serial command interface as robust as possible.

You can check out my forked library and the changes I made on my GitHub profile here: [Link to your forked GitHub repository]

PC Control via Serial Port

The final step was to control the synthesizer from my computer. I implemented a simple command-line interface over the Arduino's serial port.

The Arduino code continuously listens for commands sent from the PC via the Serial Monitor or any terminal program (like PuTTY or a custom Python script).

The command structure is simple. For example:

• SETFREQ 125000000 sets the output frequency to 125 MHz.
• SETPHASE 90 sets the phase offset to 90 degrees.
• SWEEP 100000000 150000000 1000 initiates a frequency sweep.

This approach is incredibly flexible and allows for easy automation and integration with other software.

Live Demo

Here’s a short video demonstrating the synthesizer in action. I'm using the Arduino IDE's Serial Monitor to send commands and observing the output on my oscilloscope.

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Conclusion

This project was a fantastic learning experience. It combined hardware design, low-level SPI interfacing, and practical software development. Forking an existing library was a game-changer, saving me time while allowing me to create a tool perfectly tailored to my needs.

The result is a powerful, PC-controlled DDS signal generator that will be an invaluable asset for my future RF projects. If you're considering a similar build, I highly encourage you to dive in! The AD9912 is a rewarding chip to work with, and the satisfaction of building your own custom test gear is hard to beat.