I was browsing eBay one day and I ran across a posting for the Analog Devices AD9850. The AD9850 is a chip that can produce a sinusoidal wave from about 1hz to 40mhz. Somehow the electronics dealers in Hong Kong have been able to mate the chip to a small board that provides TTL level control and then sell it for an unbelievable $8 (or less!). I know a few people have paid as little as $4 (USD) for them.
To control the AD9850 you’ll need some sort of micro-controller. Without going into too much detail you are required to send a set of serial or parallel data to the chip to set the frequency. There are numerous postings on the web detailing exactly how to do this so I won’t go into too much detail. However it has been hard to find a good AD9850 Pinout so here you go.
D0 – D7 = Parallel programming bits
GND = Ground (obvious); Vss
CLK = Serial programming clock
Latch = Serial programming latch (FQ_UD pin on 9850)
DATA = Serial programming DATA (internally tied to D7)
RST = Reset. Keep tied to GND
SQW = Square wave outputs (complementary) Duty cycle adjustable with blue pot.
SINA = Raw unfiltered AD9850 sine output
SINB = 70 MHz LPF filtered AD9850 output.
For me, the easiest way to manage the AD9850 is with an Arduino Uno. If you don’t know about the Arduino platform you should check out the official site at www.arduino.cc. I have been playing with the Arduino for only a couple of months and I already have found it to be a fantastic development platform. If you are a hobbyist tinkerer… you really can’t go wrong with one.
I have paired may AD9850 with an Arduino Uno, LCD display, Rotary encoder, and a few other small parts and have put together a very descent DDS VFO capable of any frequency between 1mhz and 30mhz (It will go to 40 if you wish). A little quick work with a protoboard and I have a nice working VFO. You can watch my video on YouTube showing how it works. I also have another video of the VFO attached to my oscilloscope.
This project is ongoing. You should be able to deduce the pin outs on all items from the Arduino Sketch but if you have questions just contact me. My schematic is a little rough as I do not tend to create them that often so let me know if you catch anything out-of-place!
Because of a lot of requests I have also created a version for IF (superhet) type receivers. The VFO now supports an Intermediate Frequency and can switch upon the HI/LOW level of one analog input on the Arduino. The IF can be anything you wish and can be additive or subtractive.
** UPDATE November, 2013 **
I have updated the sketch to write the last tuned frequency to memory and recall it upon boot-up. This is a 100% direct drop-in replacement and requires you to only upload the new sketch. The code is well documented and for those of you who modified my original sketch it should be easy enough to adapt as you see fit.
Both Arduino sketchs (IF and NON-IF), schematic, libraries, and notes are available for download here. Also, Jiri (OK1DXK) create a great drawing (aka schematic) if you wish to use an Arduino Nano. If you build something from my design please send me a picture or a video of your creation. I love to see what others do!
Or you can also send a donation via paypal to firstname.lastname@example.org (My registered PayPal address.)