A recent project has been the building of a digital VFO based around the DDS-60 kit and Arduino controller. It's a useful thing to have either as part of a homebrew transmitter or transceiver or as a piece of test equipment. It can generate RF from 1 to 60 MHz in 1 Hz steps with the stability of a crystal oscillator and can run as a QRSS beacon. It's nothing particularly original and it's not rocket science but it might be helpful for someone wanting to get started with DDS and microcontrollers. It's still a work in progress and I'll be happy if anyone wants to contribute ideas or discussion.
Information about DDS (Direct Digital Synthesizer) devices caught my attention soon after I got back into amateur radio last year after a long absence from the hobby. Years ago I was somewhat fascinated by phase locked loop synthesizers and DDS was a distant dream. DDS technology is now readily available at low cost.
The DDS-60 is a kit from George, N2APB, of Midnight Design Solutions in association with the American QRP club and New Jersey QRP Club. It's a small circuit board about 1 x 2 inches. The key component is an AD9851 chip from Analog Devices.
The DDS-60 cannot do much by itself. It needs some sort of controller to send it the correct digital commands to tell it what frequency to generate. The website gives some examples on how various people have done this. None of these were really what I wanted although I used the "DDS Controller" program by WA6UFQ to test my newly constructed DDS-60 via a PC parallel printer port. I have previous experience with Microchip PIC so I was thinking of building a PIC controller but then I listened to a great podcast all about something called the Arduino which sounded ideal for the job.
The Arduino is an open source hardware and software project aimed at making it easy for someone to get into using embedded microcontrollers. The hardware is based around the Atmel ATmega328 chip and boards are available from various manufacturers. The software development environment is a free Java based application which you run on Windows, Mac or Linux and use it to edit, compile and transfer your code to the hardware via USB. It's a very cool project with a growing community around it and an ever increasing variety of accesssories being produced. The latest Arduino board is the Duemilanove. It has 14 digital I/O pins and 6 analog inputs. I used a Duemilanove for my prototype but I rebuilt it using a compatible alternative. More about that later.