This is a simple Signal Generator built with AD9833, atmega328au.
I'm going to share some of the building experience online or in my personal blog (Which is in Simplified Chinese).
The whole idea of this project were inspired by Cezar Chrilla's How to Build Your Own Function Generator Using Analog Devices’ AD9833
The circuit part is almost the same and the only difference is the firmware, and it uses 2 awesome libs: The first one is MD_AD9833 the second one is Encoder
I've already complied the files, and you can upload it to your board easily. I also recommend to see GreatScott's Function/Waveform Generator || DIY or Buy, he made a arduino nano version of this.
Have fun!