Homebrew Signal Generator - Arduino and AD-9850 Module

 

                              

Arduino Nano and AD-9850 Signal Generator

The ability to generate a clean sine wave is incredibly useful to the electronic home-brewer. In testing a an audio or RF circuit you often need a tune-able, stable frequency source. Commercial ones range from very expensive, with the ability to generate arbitrary waves at very precise signal levels. For my purposes a simple sine wave generator with a variable attenuation meets most of my needs.

This Signal Generator is built using an AD-9850 Direct Digital Synthesizer and an Arduino Nano. It generates a clean sine wave from 0 to 62.5 MHz (very clean up to about 50 MHz, but still use-able up to 62.5. There are various versions of this floating around the internet, including prebuilt ones from a variety of sellers. The display is 16x2 I2C LCD. The control is a Rotary Digital Encoder with push button. Turn the encoder to change frequency. Push the button to select the tuning increment.

There are various versions of this floating around the internet. This is my implementation. 

The code and build instructions are available on Github at:

• https://github.com/kk4das/Signal_Generator
  

To control the AD-9850 I chose to use a DDS library written by Paul Darlington, M0XPD.  You'll need to download it from his Github repository and install it using the Arduino IDE Library Manager.  You can read Paul's original blog for details on the library.

• DDS Signal Generator Module - any one of the AD9850 boards should work. I used each of these at different times:
• https://www.amazon.com/HiLetgo-AD9850-Generator-0-40MHz-Equipment/dp/B01J7XPWNU/
• https://www.amazon.com/gp/product/B082143FD9
• https://www.analog.com/media/en/technical-documentation/data-sheets/AD9850.pdf
• 16x2 I2C LCD display
•  https://www.amazon.com/JANSANE-Arduino-Display-Interface-Raspberry/dp/B07D83DY17
• Rotary Encoder with switch
• https://www.mouser.com/ProductDetail/652-PEC11R-4020F-S24
  
• 10K linear taper potentiometer
  
• https://www.mouser.com/ProductDetail/Bourns/PDB181-K415K-103B?qs=Zq5ylnUbLm7hRcKeZmRxRw%3D%3D

Here is the wiring:

Signal Generator Wiring

Fit and finish details:

• Enclosure - 4"x3" plastic enclosure
• https://www.mpja.com/4in-X-3in-X-16in-Black-Plastic-Box-Enclosure/productinfo/15523+BX/
  
• Panel mount BNC Connector
• https://www.mpja.com/BNC-Type-Connector-UG-1094-Female-Single-Hole-Mount/productinfo/20507+RC/
• PCBs = two Adafruit 1/4 sized breadboard PCBs, one for the Arduino and one for the AD-9850 module
•  https://www.adafruit.com/product/589
• Mini toggle switch for power
• Panel mount 2.1mm DC barrel jack
  
• Mounting hardware - 4-40 standoffs and spacers, machine screws, washers and nuts
• 0.1" female headers on the breadboard make it easy to wire the components up in the case

Signal Generator Construction

And here is what the finished product looks like:

KK4DAS Signal Generator

I've been using this in my shop over the last few months to test out circuits on the Furlough-40.  It's really useful to be able to inject a known signal at various points in the circuit and see now the downstream amplifiers and filters perform  Highly recommended!

At a recent meeting of the Vienna Wireless Society I demonstrated how straightforward it is to build this.  I went from a pile of parts to a working unit in under an hour.  Here is the video from the meeting:

If you build it please let me know in comments.

73 from Great Falls

Dean

KK4DAS