Jon,
There are dozens of implementations of DDS VFOs using Arduino and the AD9850 module like yours. Be careful, as some AD9850 modules have a crystal oscillator that works fine on 5.0 volts, but others should not have more than 3.3 volts. Look for details on top of the crystal. If yours needs 3.3 volts you may drop from 5.0 volts using two diodes in series.
The easiest and most convenient way to control the frequency is with a rotary encoder, less than $5.00 on ebay. Peruse your sketch and see if you can find "#include rotary" This is a library module that deals with rotary encoders. When it is referenced in the sketch, typically you will see which pins are used to connect the encoder assembly. The encoder may be a mechanical or optical switch assembly, with or without detents. The two switches make and break in an overlapping manner as the knob is rotated. The software looks at the make-break sequence to determine if the frequency should be raised or lowered. Some encoders come with a push switch, and this is commonly used by software to set the tuning rate so that you may quickly move close to your desired frequency then reduce the rate to fine tune. I prefer the optical without detent and a heavy flywheel knob, makes tuning a breeze! To get started, an inexpensive mechanical version works fine.
For frequency readout, an alphanumeric LCD display, either 2 lines by 16 characters or 4 lines by 20 characters works well. These devices run anywhere from $6 to $15. Get the version with the I2C interface on the back, or buy it separately and solder it on the back. (You will probably need to adjust the contrast pot on the back of the interface module to see any characters.) With I2C you only need ground and 5 volts, plus two more wires, SDA (Serial Data) connected to Arduino A4, and SCK (Serial Clock) connected to Arduino A5. You will need to set the correct I2C address in software to match the device. A simple "I2C Scanner" may be loaded into Arduino to verify proper connections and identify the correct address. Google I2C Scanner and download one from github or arduino playground.
For a good understanding, look at the implementation by K2ZIA at this link, which includes schematic and software. You will then see how to connect the display and the rotary encoder:
http://www.farrukhzia.com/k2zia/There are many different ways to configure the I/O devices on the Arduino. The Nano in the K2ZIA and your UNO are almost identical functionally. Look first at which pins are connected to the DDS module. Typically you need four signals, Clock, Load (FQ_UD) Serial Data, and Reset. Look at the source code for your sketch to see which pins are connected to these signals. Then you can avoid conflicts when adding the rotary encoder.
The encoder is often configured using interrupt-capable pins, but other people may poll the encoder switches and use general purpose pins, either digital or analog.
You could easily use the K2ZIA sketch and wire your devices as in his schematic and you will be off and running. Or, compare his sketch and I/O pin assignments to the sketch you loaded and you will have a much better understanding of how to control and display frequency.
Later on, you might want to add a GPS module and lock in calibration with the satellites. Google Gene Marcus, W3PM, he has a good implementation using the same DDS and Arduino you are using.
By the way, it would be much easier to interconnect everything if you purchase some dupont wires! You do not need the ZIA circuit board, It can all be done in a chassis like you have, or on a proto board. I did mine with a Nano. If you really want to get proficient with Arduino, check out "Random Nerd Tutorials" by Rui Santos, all free on the web.
Hope this helps....
73, Rick
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